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Results for “Biochemistry”

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bioRxiv2018

Proteomics reveals profound metabolic changes in the alcohol use disorder brain

Changes in brain metabolism are a hallmark of Alcohol Use Disorder (AUD). Determining how AUD changes the brain proteome is critical for understanding the effects of alcohol consumption on biochemical processes in the brain. We used data-independent acquisition mass spectrometry proteomics to study differences in the abundance of proteins associated with AUD in pre-frontal lobe and motor cortex from autopsy brain. AUD had a substantial effect on the overall brain proteome exceeding the inherent differences between brain regions. Proteins associated with glycolysis, trafficking, the cytoskeleton, and excitotoxicity were altered in abundance in AUD. We observed extensive changes in the abundance of key metabolic enzymes, consistent with a switch from glucose to acetate utilization in the AUD brain. We propose that metabolic adaptations allowing efficient acetate utilization contribute to ethanol dependence in AUD.

biochemistry↗

bioRxiv2018

LRRK2 exonic variants associated with Parkinson’s disease augment phosphorylation levels for LRRK2-Ser1292 and Rab10-Thr73

Leucine-rich repeat kinase 2 (LRRK2) is associated to Parkinsons disease (PD). The most common form of LRRK2 PD is caused by the G2019S variant. Besides G2019S, eight other LRRK2 variants causing familial PD also have amino acid substitutions located in a LRRK2 enzymatic domainsuggesting that enzymatic activity is at the core of mechanisms underlying disease risk. Common LRRK2 polymorphic risk variations such as G2385R, A419V, R1628 and M1646T all reside in other LRRK2 domains. Prior knowledge is limited on how these variants influence LRRK2 function. To investigate the impact on enzymatic function of both rare and common LRRK2 variation a comprehensive profiling of nineteen LRRK2 exonic variants was pursued. Six LRRK2 phosphorylation sites were identified by mass spectrometry. Besides already known phosphorylation sites such as Ser910, Ser935, Ser955, Ser973 and Ser1292 also Thr826 was confirmed by a targeted MRM assay as a LRRK2 phosphorylation site in mammalian cells. Phosphorylation site occupancy for all six LRRK2 sites was obtained but no obvious correlation to risk of disease was found. Instead, application of phospho-specific antibodies targeting LRRK2 phosphorylation sites confirmed that autophosphorylation at Ser1292 was significantly increased for all disease-causing variants whereas no significant differences could be observed for the common intermediate risk variants. Recently, Rab10 and Rab12 have been shown to be bona fide LRRK2 substrates and we find that both rare and common LRRK2 exonic variants augment the phosphorylation of Rab10. This was not observed with Rab12. Furthermore, the protective variant N551K has reduced Rab10 phosphorylation compared to LRRK2 WT. This was not observed with the protective variant R1398H. Our findings support the hypothesis that increased LRRK2 kinase function is associated with increased PD risk but also highlights the need for more sensitive tools for detection of increases in kinase activity in carriers of LRRK2 PD risk variants.\n\nAbbreviations

biochemistry↗

bioRxiv2018

The three dimensional structure of Bovine Salivary Protein 30b (BSP30b) and its interaction with specific rumen bacteria

Bovine Salivary Protein 30b (BSP30b) is a member of the tubular lipid-binding (TULIP) superfamily that includes the human bactericidal/permeability-increasing proteins (BPI), lipopolysaccharide binding proteins (LBP) and palate, lung, and nasal epithelium carcinoma-21 associated proteins (PLUNC). BSP30b is most closely related to the PLUNC family and is predominantly found in bovine saliva. There are four BSP30 isoforms (BSP30a-d) and collectively, they are the most abundant protein component of bovine saliva. The PLUNC family members are proposed to be lipid binding proteins, although in most cases their lipid ligands are unknown. Here, we present the X-ray crystal structure of BSP30b at 2.0 [A] resolution. We used a double methionine mutant and Se-Met SAD phasing to solve the structure. The structure adopts a curved cylindrical form with a hydrophobic channel formed by an /{beta} wrap, which is consistent with the TULIP superfamily. The structure of BSP30b in complex with oleic acid is also presented where the ligand is accommodated within the hydrophobic channel. The electron density for oleic acid suggests that the ligand is only partially occupied in the binding site implying that oleic acid may not be the preferred ligand. GFP-tagged BSP30b binds to the surface of olive oil droplets, as observed under fluorescent microscopy, and acts as a surfactant consistent with its association with decreased susceptibility to bloat in cattle. Bacteria extracted directly from bovine rumen contents indicate that the GFP_BSP30b fusion protein binds to a small number of selected bacterial species in vivo. These results suggest that BSP30b may bind to bacterial lipids from specific species and that this abundant protein may have important biological roles via interacting with rumen bacteria during feeding and rumination.

biochemistry↗

bioRxiv2018

Macrophage migration inhibitory factor (MIF) of Syrian golden hamster (Mesocricetus auratus) has similar structure and function as human MIF and promotes pancreatic tumor growth in vivo

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that increasingly is being studied in cancers and inflammatory diseases. Though murine models have been instrumental in understanding the functional role of MIF in different pathological conditions, the information obtained from these models is biased towards a specific species. In experimental science, results obtained from multiple clinically relevant animal models always provide convincing data that might recapitulate in humans. Syrian golden hamster (Mesocricetus auratus), is a clinically relevant animal model for multiple human diseases. Hence, the major objectives of this study were to characterize structure and function of hamster MIF, and finally evaluate its effect on pancreatic tumor growth in vivo. Initially, the recombinant hamster MIF (rha-MIF) was cloned, expressed and purified in bacterial expression system. The rha-MIF primary sequence, biochemical properties and crystal structure analysis showed a greater similarity with human MIF. The crystal structure of hamster MIF illustrates that it forms a homotrimer as known in human and mouse. However, hamster MIF exhibits some minor structural variations when compared to human and mouse MIF. The in vitro functional studies show that rha-MIF has tautomerase activity and enhances activation and migration of hamster peripheral blood mononuclear cells (PBMCs). Interestingly, injection of rha-MIF into HapT1 pancreatic tumor bearing hamsters significantly enhanced the tumor growth and tumor associated angiogenesis. Together, the current study shows a structural and functional similarity between hamster and human MIF. Moreover, it has demonstrated that a high-level of circulating MIF originating from non-tumor cells might also promote pancreatic tumor growth in vivo.

biochemistry↗

bioRxiv2018

Investigating the cytotoxic effects of the venom proteome of two species of the Viperidae family (Cerastes cerastes and Cryptelytrops purpureomaculatus) from various habitats

Animal secretions are of great interest in terms of drug development due to their complex protein and peptide composition. Especially, in the field of therapeutic medications such as anti-cancer drugs snake venoms receive attention. In this study we report of two Viperidae species from various habitats with a particular focus on the cytotoxic potential along with the decomplexation of the venom proteome: the horned desert viper (Cerastes cerastes), native to desert regions of North Africa and the mangrove pit viper (Cryptelytrops purpureomaculatus), found in coastal forests of Southeast Asia. Initial cytotoxic screenings of the crude venoms revealed diverse activity, with the highest effect against SHSY5Y human glioblastoma carcinoma cells compared to other cancerous and non-cancerous cell lines. In-depth cytotoxicity studies of SHSY5Y cells with purified venom fractions revealed dimeric disintegrins from C. cerastes venom which exerted a high cytotoxic activity with IC50 values from 0.11 to 0.58{micro}M and the disintegrins-like effect on SHSY5Y morphology was observed due to cell detachment. Furthermore, two polyproline BPP-related peptides, one PLA2 and a peptide-rich fraction were determined for C. purpureomaculatus with moderate IC50 values between 3-51{micro}M. Additionally, the decryption of the venom proteomes by snake venomic mass spectrometry and comparison of same species from different habitats revealed slight differences in the composition.

biochemistry↗

bioRxiv2018

Comparative metabonomic investigations of Schistosoma japonicum from SCID mice and BALB/c mice: clues to developmental abnormality of schistosome in the immunodeficient host

It has been discovered that the development of schistosome is hampered in immunodeficient mice, e.g. nude mice lacking T-lymphocytes and the severe combined immune deficient (SCID) mice lacking both T- and B-lymphocytes. However, its still unresolved about the underlying regulatory mechanisms of the retarded growth and development of schistosomes in their immunodeficient definitive host. In this study, therefore, five replicates of male or female Schistosoma japonicum samples with twenty male or female worms in each sample, were collected from SCID mice or BALB/c mice at five weeks post infection and used to perform metabonomic analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) platform, for elucidating the growth and development regulation of schistosome in their definitive hosts from the metabolomic aspect. Based on the identified 1015 ion features in ESI+ mode and 342 ion features in ESI-mode, multivariate modelling methods including the Principal Component Analysis (PCA), Partial Least Squares Discriminant Analysis (PLS-DA) and Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) identified distinct metabolic profiles that clearly differentiated both male and female worms in SCID mice from those in BALB/c mice, respectively. Common and uniquely perturbed metabolites and their involved metabolic pathways were identified in male and female worms from SCID mice when compared with those from BALB/c mice. The results also revealed that more differential metabolites were found in female worms (one metabolite was up-regulated and forty metabolites were down-regulated) than male worms (nine metabolites were up-regulated and twenty metabolites were down-regulated) between SCID mice and BALB/c mice. The top five increased metabolites of male worms in SCID mice when compared with those in BALB/c mice were PC(22:6/20:1), L-allothreonine, L-serine, glycerophosphocholine and 5-aminoimidazole ribonucleotide. And the top five decreased metabolites of male worms in SCID mice when compared with those in BALB/c mice were PC(16:0/0:0), PAF C-16, PE(18:1/0:0), adenosine and butenoyl PAF. Most of the differential metabolites of female worms in SCID mice had lower levels when compared with the normal female worms in BALB/c mice, except for retinyl ester with a higher level. The top five decreased metabolites of female worms in SCID mice when compared with those in BALB/c mice were adrenic acid, 5-phosphoribosylamine, PC(16:0/0:0), PC(22:6/20:1) and ergothioneine. The involved metabolic pathways of the differential metabolites in male worms between SCID mice and BALB/c mice mainly included taurine and hypotaurine metabolism, glycerophospholipid metabolism, sphingolipid metabolism, arachidonic acid metabolism, alpha-linolenic acid metabolism, etc. The involved metabolic pathways of differential metabolites in female worms included mainly pyrimidine metabolism, sphingolipid metabolism, arachidonic acid metabolism, glycerophospholipid metabolism, tryptophan metabolism, etc. These findings suggested a correlation between the retarded growth and development of schistosome in SCID mice and their perturbed metabolic profiles, which also provided a new insight into the regulation mechanisms of growth and development of S. japonicum worms from the metabolic level, and provided clues for discovery of drugs or vaccines against the parasites and parasitic disease.\n\nAuthor summaryThe growth and development of schistosome has been discovered hampered in the immunodeficient hosts. But it remains unresolved about the molecular mechanisms involved in this. In this study, we tested and compared the metabolic profiles of the male and female Schistosoma japonicum worms collected from SCID mice or BALB/c mice at five weeks post infection using liquid chromatography tandem mass spectrometry (LC-MS/MS) platform. There were 1015 ion features in ESI+ mode and 342 ion features in ESI-mode were identified, and distinct metabolic profiles were found to clearly differentiate both male and female worms in SCID mice from those in BALB/c mice, respectively. The results also found more differential metabolites in female worms than in male worms between SCID mice and BALB/c mice. The enriched metabolic pathways of the differential metabolites in male worms between SCID mice and BALB/c mice included taurine and hypotaurine metabolism, glycerophospholipid metabolism, sphingolipid metabolism, arachidonic acid metabolism, alpha-linolenic acid metabolism, etc. And the enriched metabolic pathways of differential metabolites in female worms included pyrimidine metabolism, sphingolipid metabolism, arachidonic acid metabolism, glycerophospholipid metabolism, tryptophan metabolism, etc. The findings in this study suggested an association between the developmentally stunted schistosome and their perturbed metabolites and metabolic pathways, which provided a new insight into the regulation mechanisms of growth and development of S. japonicum worms from the metabolic level, and clues for discovery of drugs or vaccines against the parasites and disease.

biochemistry↗

bioRxiv2018

Sequential digestion with Trypsin and Elastase in cross-linking/mass spectrometry

Cross-linking/mass spectrometry has become an important approach for studying protein structures and protein-protein interactions. The amino acid composition of some protein regions impedes the detection of cross-linked residues, although it would yield invaluable information for protein modelling. Here, we report on a sequential digestion strategy with trypsin and elastase to penetrate regions with a low density of trypsin cleavage sites. We exploited intrinsic substrate recognition properties of elastase to specifically target larger tryptic peptides. Our application of this protocol to the TAF4-12 complex allowed us to identify cross-links in previously inaccessible regions.

biochemistry↗

bioRxiv2018

The dynamic and structural properties of axonemal tubulins support the high length stability of cilia

Cilia and flagella, which play essential roles in cell motility, sensing and development, contain at their core a microtubule-based structure called axoneme. The axoneme, which contains nine doublet and two central microtubules, is highly stable and its length is precisely-controlled. We have asked whether the axonemal tubulins contribute to this length stability. Towards this end, we used a novel procedure to differentially extract the tubulins from the different axoneme components, and characterized their dynamic properties and post-translational modifications (PTMs). We found that their dynamic properties are consistent with the greater stability of axonemes. Despite the differences in PTMs between the axonemal components, we found no significant differences in their dynamic properties. Unexpectedly, the reconstituted ciliary microtubules exhibit curved protofilaments at their growing tip, that may correspond to the fluctuating GTP-cap hypothesized to exist. Thus, our study provides new insights into the growth, stability and the role of PTMs of ciliary tubulin.\n\nAbbreviations

biochemistry↗

bioRxiv2018

SPR-measured kinetics of PROTAC ternary complexes influence target degradation rate

Bifunctional degrader molecules, known as proteolysis-targeting chimeras (PROTACs), function by recruiting a target to an E3 ligase, forming a target:PROTAC:ligase ternary complex. Despite the importance of this key intermediate species, no detailed validation of a method to directly determine binding parameters for ternary complex kinetics has been reported, and it remains to be addressed whether tuning the kinetics of PROTAC ternary complexes may be an effective strategy to improve the efficiency of targeted protein degradation. Here, we develop an SPR-based assay to quantify the stability of PROTAC-induced ternary complexes by measuring for the first time the kinetics of their formation and dissociation in vitro using purified proteins. We benchmark our assay using four PROTACs that target the bromodomains (BDs) of BET proteins Brd2, Brd3 and Brd4 to the E3 ligase VHL. We reveal marked differences in ternary complex off-rates for different PROTACs that exhibit either positive or negative cooperativity for ternary complex formation relative to binary binding. The positively cooperative degrader MZ1 forms comparatively stable and long-lived ternary complexes with either Brd4BD2 or Brd2BD2 and VHL. Equivalent complexes with Brd3BD2 are destabilised due to a single amino acid difference (Glu/Gly swap) present in the bromodomain. We observe that this difference in ternary complex dissociative half-life correlates to a greater initial rate of intracellular degradation of Brd2 and Brd4 relative to Brd3. These findings establish a novel assay to measure the kinetics of PROTAC ternary complexes and elucidate the important kinetic parameters that drive effective target degradation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/451948v2_ufig2.gif" ALT="Figure 2"> View larger version (32K): org.highwire.dtl.DTLVardef@10e7c1eorg.highwire.dtl.DTLVardef@1f6a57forg.highwire.dtl.DTLVardef@1eb6e46org.highwire.dtl.DTLVardef@194cb2a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2018

Toxic Determinants of Staphylococcus aureus PSMα3 Cross-α Amyloid

The phenol-soluble modulin (PSM) peptide family, secreted by Staphylococcus aureus, performs various virulence activities, some mediated by the formation of amyloid fibrils of diverse architectures. Specifically, PSM1 and PSM4 structure the S. aureus biofilm by assembling into robust cross-{beta} amyloid fibrils. PSM3, the most cytotoxic member of the family, assembles into cross- fibrils in which -helices stack into tightly mated sheets, mimicking the cross-{beta} architecture. Here we demonstrated that massive T-cell deformation and death is linked with PSM3 aggregation and co-localization with cell membranes. Our extensive mutagenesis analyses supported the role of positive charges, and especially Lys17, in interactions with the membrane, and suggested their regulation by inter- and intra-helical electrostatic interactions within the cross- fibril. We hypothesize that PSM3 cytotoxicity is governed by the ability to form cross- fibrils and involves a dynamic process of co-aggregation with cell membrane, rupturing it. HighlightsO_LIThe cytotoxic S. aureus PSM3 assembles into cross- fibrils C_LIO_LICross- fibril polymorphism and mutations-induced secondary structure switching C_LIO_LIRegulation by cross- fibril inter- and intra-helical electrostatic interactions C_LIO_LIToxicity as a putative dynamic process of PSM3 co-aggregation with membranes C_LI

biochemistry↗

bioRxiv2018

A Novel analog approach for fast evaluation of affinity between ligand and receptor in scaled up molecular models

Rational structure based drug design aims at identifying ligand molecules that bind to the active site of a target molecule with high affinity (low binding free energy), to promote or inhibit certain biofunctions. Thus, it is absolutely essential that one can evaluate such affinity for the predicted molecular complexes in order to design drugs effectively. A key observation is that, binding affinity is proportional to the geometric fit between the two molecules. Having a way to assess the quality of the fit enables one to rank the quality of potential drug solutions. Other than experimental methods that are associated with excessive time, labor and cost, several in silico methods have been developed in this regard. However, a main challenge of any computation-based method is that, no matter how efficient the technique is, the trade-off between accuracy and speed is inevitable. Therefore, given todays existing computational power, one or both is often compromised. In this paper, we propose a novel analog approach, to address the aforementioned limitation of computation-based algorithms by simply taking advantage of Kirchhoffs circuit laws. Ligand and receptor are represented with 3D printed molecular models that account for the flexibility of the ligand. Upon the contact between the ligand and the receptor, an electrical current will be produced that is proportional to the number of representative contact points between the two scaled up molecular models. The affinity between the two molecules is then assessed by identifying the number of representative contact points obtainable from the measured total electrical current. The simple yet accurate proposed technique, in combination with our previously developed model, Assemble-And-Match, can be a breakthrough in development of tools for drug design. Furthermore, the proposed technique can be more broadly practiced in any application that involves assessing the quality of geometric match between two physical objects.

biochemistry↗

bioRxiv2018

Characterisation of a type II functionally-deficient variant of alpha-1-antitrypsin discovered in the general population

Lung disease in alpha-1-antitrypsin deficiency (AATD) results from dysregulated proteolytic activity, mainly by neutrophil elastase (HNE), in the lung parenchyma. This is the result of a substantial reduction of circulating alpha-1-antitrypsin (AAT) and the presence in the plasma of inactive polymers of AAT. Moreover, some AAT mutants have reduced intrinsic activity toward HNE, as demonstrated for the common Z mutant, as well as for other rarer variants. Here we report the identification and characterisation of the novel AAT reactive centre loop variant Gly349Arg (p.G373R) present in the ExAC database. This AAT variant is secreted at normal levels in cellular models of AATD but shows a severe reduction in anti-HNE activity. Biochemical and molecular dynamics studies suggest it exhibits unfavourable RCL presentation to cognate proteases and compromised insertion of the RCL into {beta}-sheet A. Identification of a fully dysfunctional AAT mutant that does not show a secretory defect underlines the importance of accurate genotyping of patients with pulmonary AATD manifestations regardless of the presence of normal levels of AAT in the circulation. This subtype of disease is reminiscent of dysfunctional phenotypes in antithrombin and C1-inibitor deficiencies so, accordingly, we classify this variant as the first pure functionally-deficient (type II) AATD mutant.

biochemistry↗

bioRxiv2018

Effects of inflammation-induced oxidation on the dimerization of fibrinogen αC domain

Upon activation, fibrinogen is converted to insoluble fibrin, which assembles into long strings called protofibrils. These aggregate laterally to form a fibrin matrix that stabilizes a blood clot. Lateral aggregation of protofibrils is mediated by the C domain, a partially structured fragment located in a disordered region of fibrinogen. Polymerization of C domains links multiple fibrin molecules with each other enabling the formation of thick fibrin fibers and a fibrin matrix that is stable but can also be digested by enzymes. How-ever, oxidizing agents produced during the inflammatory response have been shown to cause thinner fibrin fibers resulting in denser clots, which are harder to proteolyze and pose the risk of deep vein thrombosis and lung embolism. It has been postulated that oxidation of Met476 located within the C domain hinders its ability to polymerize disrupting the lateral aggregation of protofibrils and leading to the observed thinner fibers. How C domains assemble into polymers is still unclear and yet this knowledge would shed light on the mechanism through which oxidation weakens the lateral aggregation of protofibrils. This study used temperature replica exchange molecular dynamics simulations to investigate the C-domain dimer and how this is affected by oxidation of Met476. The results suggest that multiple binding modes between two alphaC domains can occur and that oxidation decreases the likelihood of dimer formation. Furthermore, the side chain of Met476 acts as a docking spot between C domains and this function is abrogated by its conversion to methionine sulfoxide.

biochemistry↗

bioRxiv2018

Interplay between substrate recognition, 5’ end tRNA processing and methylation activity of human mitochondrial RNase P

Human mitochondrial ribonuclease P (mtRNase P) is an essential three protein complex that catalyzes the 5 end maturation of mitochondrial precursor tRNAs (pre-tRNAs). MRPP3 (Mitochondrial RNase P Protein 3), a protein-only RNase P (PRORP), is the nuclease component of the mtRNase P complex and requires a two-protein S-adenosyl methionine (SAM)-dependent methyltransferase MRPP1/2 sub-complex to function. Dysfunction of mtRNase P is linked to several human mitochondrial diseases, such as mitochondrial myopathies. Despite its central role in mitochondrial RNA processing, little is known about how the protein subunits of mtRNase P function synergistically. Here we use purified mtRNase P to demonstrate that mtRNase P recognizes, cleaves, and methylates some, but not all, mitochondrial pre-tRNAs in vitro. Additionally, mtRNase P does not process all mitochondrial pre-tRNAs uniformly, suggesting the possibility that some pre-tRNAs require additional factors to be cleaved in vivo. Consistent with this, we found that addition of the MRPP1 co-factor SAM enhances the ability of mtRNase P to bind and cleave some mitochondrial pre-tRNAs. Furthermore, the presence of MRPP3 can enhance the methylation activity of MRPP1/2. Taken together, our data demonstrate that the subunits of mtRNase P work together to efficiently recognize, process and methylate human mitochondrial pre-tRNAs.

biochemistry↗

bioRxiv2018

ILEX PARAGUARIENSIS, EXERCISE AND CARDIOPROTECTION: A retrospective analysis

Studies on strategies to generate cardioprotective effects have been on the rise. Previous work by our group with an ex vivo model of ischemia/reperfusion has shown that both the short-term consumption of yerba mate and exercise can each induce protection of cardiac function independently. Surprising, the two strategies together do not, with an apparent loss of their respective cardioprotection activity. To improve our understanding of the mechanisms involved without reperforming the experiments, we have conducted a retrospective data science-analysis that have produced new insights. The analysis shows that yerba mate generated reductive stress. Alone, this stress increased redox damage in the heart that appears to have led to a protective conditioning. In combination with exercise, the effects of mate inhibited the intermittent ROS generation promoted by exercise alone, which diminished the adaptive response in the heart. These results suggest that an understanding of the molecular mechanisms involved with the yerba mate-promoted reductive stress in cardiac tissue could lead to improved strategies to induce cardioprotection.

biochemistry↗

bioRxiv2018

Divalent cations can control a switch-like behavior in heterotypic and homotypic RNA coacervates

Liquid-liquid phase separation (LLPS) of RNA-protein complexes plays a major role in the cellular function of membraneless organelles (MLOs). MLOs are sensitive to changes in cellular conditions, such as fluctuations in cytoplasmic ion concentrations. To investigate the effect of these changes on MLOs, we studied the influence of divalent cations on the physical and chemical properties of RNA coacervates. Using a model arginine-rich peptide-RNA system, we predicted and observed that variations in signaling cations exert interaction-dependent effects on RNA LLPS. Changing the ionic environment has opposing effects on the propensity for heterotypic peptide-RNA and homotypic RNA LLPS, which results in a switch between coacervate types. Furthermore, divalent ion variations continuously tune the microenvironments and fluid properties of heterotypic and homotypic droplets. Our results may provide a generic mechanism for modulating the biochemical environment of RNA coacervates in a cellular context.

biochemistry↗

bioRxiv2018

Rational construction of compact de novo-designed biliverdin-binding proteins

AbstractWe report the rational construction of a de novo-designed biliverdin-binding protein by first principles of protein design, informed by energy minimization modeling in Rosetta. The self-assembling tetrahelical bundles bind biliverdin IXa (BV) cofactor auto-catalytically in vitro, similar to photosensory proteins that bind BV (and related bilins, or linear tetrapyrroles) despite lacking sequence and structural homology to the natural counterparts. Upon identifying a suitable site for cofactor ligation to the protein scaffold, stepwise placement of residues stabilized BV within the hydrophobic core. Rosetta modeling was used in the absence of a high-resolution structure to define the structure-function of the binding pocket. Holoprotein formation indeed stabilized BV, resulting in increased far-red BV fluorescence. By removing segments extraneous to cofactor stabilization or bundle stability, the initial 15-kilodalton de novo-designed fluorescence-activating protein (\"dFP\") was truncated without altering its optical properties, down to a miniature 10-kilodalton \"mini,\" in which the protein scaffold extends only a half-heptad repeat beyond the hypothetical position of the bilin D-ring. This work demonstrates how highly compact holoprotein fluorochromes can be rationally constructed using de novo protein design technology and natural cofactors.

biochemistry↗

bioRxiv2018

Structural basis for prodrug recognition by the SLC15 family of proton coupled peptide transporters

A major challenge in drug development is the optimisation of intestinal absorption and cellular uptake. A successful strategy has been to develop prodrug molecules, which hijack solute carrier (SLC) transporters for active transport into the body. The proton coupled oligopeptide transporters, PepT1 and PepT2, have been successfully targeted using this approach. Peptide transporters display a remarkable capacity to recognise a diverse library of di- and tri-peptides, making them extremely promiscuous and major contributors to the pharmacokinetic profile of several important drug classes, including beta-lactam antibiotics, anti-viral and antineoplastic agents. Of particular interest has been their ability to recognise amino acid and peptide-based prodrug molecules, thereby providing a rational approach to improving drug transport into the body. However, the structural basis for prodrug recognition has remained elusive. Here we present crystal structures of a prokaryotic homologue of the mammalian transporters in complex with the antiviral prodrug valacyclovir and the peptide based photodynamic therapy agent, 5-aminolevulinic acid. The valacyclovir structure reveals that prodrug recognition is mediated through both the amino acid scaffold and the ester bond, which is commonly used to link drug molecules to the carriers physiological ligand, whereas 5-aminolevulinic acid makes far fewer interactions compared to physiological peptides. These structures provide a unique insight into how peptide transporters interact with xenobiotic molecules and provide a template for further prodrug development.

biochemistry↗