Biology subjects

Schaffitzel, C.

Publications and source records attributed to Schaffitzel, C..

At least 19 recordsLinked to original sources

bioRxiv2026

Structural heterogeneity of uncrosslinked FtsH-HflKC assemblies includes variable FtsH occupancy and a distinct wild-type FtsH architecture

The AAA+ metalloprotease FtsH associates with HflK and HflC to form the megadalton FtsH-HflKC complex (FHC), which contributes to membrane-protein quality control in Escherichia coli. Recent structural studies have revealed asymmetric HflKC architectures and variable FtsH occupancy, contrasting with earlier crosslinked structures of a symmetric four-hexamer cage. Here, we analyzed wild-type, uncrosslinked FHC co-expressed from a single multicistronic plasmid and solubilized in lauryl maltose neopentyl glycol (LMNG) using single-particle cryo-EM, SEC-SAXS, and biochemical activity assays. Two-dimensional classification identified HflKC-containing particles associated with one or two FtsH hexamers, together with a distinct population of isolated FtsH particles. Focused reconstruction of the FtsH cytosolic domain reached 5.32 angstrom resolution and provided a structural view of wild-type, uncrosslinked FtsH without stabilizing substitutions or an added nucleotide analogue. The reconstruction retained the characteristic stacked arrangement of the AAA+ and protease rings but showed a more laterally splayed AAA+ ring compared with the stabilized reference, while the protease ring remained broadly similar in overall envelope. A 9.63 angstrom HflKC consensus reconstruction and 3D variability analysis (3DVA) in C1, further revealed substantial conformational variability spanning open-like and more constricted scaffold geometries. SEC-SAXS of a selected later-eluting LMNG-solubilized fraction yielded a compact anisotropic envelope with an estimated Dmax of ~110-115 angstrom, although this species could not be assigned to a defined intact FHC stoichiometry. Under the conditions tested, the FHC preparation also showed lower apparent ATPase and proteolytic activities than isolated FtsH. Together, these findings highlight the compositional and conformational heterogeneity of uncrosslinked FHC and reveal a more laterally splayed AAA+ arrangement in wild-type FtsH compared with the stabilized reference structure.

biophysics↗

bioRxiv2026

Recombinant Echis disintegrins reveal distinct inhibitory profiles on platelet aggregation and endothelial cell migration

Disintegrins are snake venom toxins that bind integrins and modulate platelet aggregation and cell migration. Isolation from venom often yields insufficient quantities for comprehensive study, making recombinant expression essential for detailed toxin characterisation. Here, we produced and characterised four disintegrins from Echis coloratus and Echis ocellatus in Escherichia coli. These homologous proteins contain distinct integrin-binding motifs: EcDis_RGD, EoDis_RGD, EcDis_KGD, and EcDis_VGD. Functional activities were evaluated using human platelet aggregation and endothelial cell scratch wound-healing assays. RGD-containing disintegrins exhibited the strongest inhibition of platelet aggregation, with EcDis_RGD showing the highest potency. The EcDis_KGD disintegrin inhibited platelet aggregation less potently, whereas EcDis_VGD showed no detectable activity in our assays. In endothelial cells, EcDis_RGD disintegrin markedly impaired cell migration, while EoDis_RGD displayed weaker anti-migratory activity. Neither KGD- nor VGD-containing disintegrins significantly affected wound closure. EoDis_RGD exhibited similar antiplatelet activity to the native, venom-purified disintegrin ocellatusin, validating our recombinant expression strategy. However, the corresponding PII-SVMP preparation displayed reduced inhibitory activity, consistent with incomplete generation of fully mature disintegrins species. Our findings demonstrate the importance of both integrin-binding motif identity and surrounding sequence context in determining disintegrin function, and support further use of recombinant toxins in toxinology and as therapeutic lead molecules.

biochemistry↗

bioRxiv2026

Disintegrin-like and Cysteine-rich Domains Govern Enzymatic Activity and Substrate Recognition in Echis Snake Venom Metalloproteinases

Snake venom metalloproteinases (SVMPs) are major drivers of pathology following viper envenomation and represent important targets for the development of next-generation recombinant antivenoms. PIII SVMPs are among the most potent haemorrhagic toxins and contain disintegrin-like (Dis) and cysteine-rich (C-rich) accessory domains. Despite their biomedical importance, the mechanistic roles of these accessory domains in substrate recognition and catalysis remain poorly understood. We produced recombinant full-length and domain-deletion variants of two functionally distinct PIII SVMPs: the broadly proteolytic, cytotoxic cPIII and the highly specific prothrombin activator Ecarin. Proteins were expressed as latent zymogens in insect cells, auto-activated by Zn2+, and analysed using enzymatic, blood clotting, and cell-based assays. Progressive removal of the C-rich and Dis domains reduced zymogen auto-activation and markedly diminished catalytic activity in both toxins. In cPIII, domain deletion caused a stepwise loss of proteolytic and cytotoxic activity without altering substrate preference. In Ecarin, removal of the accessory domains strongly impaired prothrombin activation, and thus plasma clotting, demonstrating a critical role in substrate recognition. Conversely, deletion of the C-rich domain increased fibrinogenolytic activity, revealing a substrate-dependent gatekeeping function. Deglycosylation showed that N-linked glycans modulate SVMP activity in a construct-dependent manner. Recombinant Ecarin closely recapitulated the biochemical properties of the native venom-derived toxin. Our data support a model in which PIII SVMP accessory domains enhance substrate positioning and catalytic efficiency while selectively restricting access to non-cognate substrates. These findings establish accessory-domain-mediated substrate recognition as a key determinant of SVMP function, informing rational antivenom design.

biochemistry↗

bioRxiv2025

pH-induced structural changes in SARS-CoV-2 spike variants

pH critically influences SARS-CoV-2 infectivity and stability by, for example, triggering pH-dependent conformational changes in the spike glycoprotein that can facilitate membrane fusion and viral entry into host cells. Using the emerging dynamical nonequilibrium molecular dynamics (D-NEMD) simulations approach, we investigated how biologically relevant pH shifts affect the functional dynamics of the fully glycosylated spike from the ancestral, Delta, and Omicron BA.1 variants of concern. For this, over 1100 nonequilibrium simulations were conducted to capture the pH-induced structural and dynamic changes that occur following transitions from physiological to acidic and alkaline conditions, with the former mimicking the low pH environment within endosomes, and the latter the high pH conditions accessible to nascent exhaled aerosols. D-NEMD reveals that pH changes trigger distinct, variant-specific conformational responses in key regions of the spike, including the receptor binding domain (RBD), fusion peptide proximal region (FPPR), and C-terminal domain (CTD). The ancestral spike shows broad pH sensitivity, characterised by directional motions and region-specific structural rearrangements that depend on the pH conditions. The spike of the Delta variant displays increased reactivity to alkaline pH, potentially explaining its reduced stability in alkaline aerosols. The spike of Omicron BA.1, in contrast, responds strongly to acidic conditions with spontaneous RBD opening and pronounced structural rearrangements in the FPPR and CTD. This behaviour aligns with this variants preference for endosomal entry and reduced reliance on TMPRSS2-mediated fusion. The Omicron BA.1 spike also shows increased resilience to alkaline pH, suggesting greater environmental stability. Our findings further emphasise the key role of glycans in spike activation, with glycan N234 stabilising the RBD "up" conformation during pH-induced transitions in Omicron under acidic conditions. These insights, together, highlight pH as a potential evolutionary pressure for SARS-CoV-2 and underscore the importance of glycosylation and environmental pH variability in shaping the behaviour of viral fusion proteins.

biochemistry↗

bioRxiv2025

Cryo-EM structure of the FtsH periplasmic domain reveals functional dynamics

FtsH, an essential AAA+ metalloprotease, maintains cellular homeostasis by degrading misfolded and membrane-associated proteins. Here, we report cryo-EM structures of the Escherichia coli FtsH periplasmic domain (FtsH-PD) revealing insights into its conformational flexibility. Initial 2D class averages suggested three distinct orientations, right-handed and left-handed maps of FtsH-PD, and a map with a different conformation. The 4.9 [A] structure of FtsH-PD exhibits the conserved +{beta} fold, while the 7.3 [A] map with the different conformation displays a 20{o} clockwise rotation of two alpha helices. These findings support a model where conformational changes are present not only in the FtsH cytosolic domain, but also in the periplasmic domain and potentially facilitate substrate translocation through a combination of mechanisms involving both the FtsH-PD and the HflKC complexed with FtsH, along with lipid-scramblase activity to assist in membrane protein extraction. This study points out novel perspectives on how conformational changes in the periplasmic domain contribute to FtsH substrate degradation mechanisms.

biochemistry↗

bioRxiv2025

Efficient Recombinant Production and Functional Characterisation of Cytotoxic and Haemotoxic Snake Venom Metalloproteinases

Snake venoms contain diverse mixtures of toxins that evolved to incapacitate prey, but in humans they cause extensive pathology following snakebite envenomation. In viper venom, some of the most potent toxins are the haemorrhagic and coagulopathic snake venom metalloproteinases (SVMPs). Because venoms contain a SVMP cocktail, and due to their cytotoxicity, SVMP characterizations have been hampered by the lack of purified enzymes. By incorporating their prodomain, which blocks the active SVMP site, we overcame their cytotoxicity and enabled recombinant production of zymogens from all three structurally variable SVMP classes (PI, PII and PIII) using our baculovirus/insect cell expression system. Zymogens were auto-activated by incubation with Zn2+ ions, resulting in prodomain cleavage, PII disintegrin cleavage and PIII prodomain proteolysis. Auto-activated SVMPs were characterized using protein substrate degradation, platelet aggregation and blood coagulation assays, benchmarked to native venom-purified SVMP. Our recombinant zymogen production protocol is generically applicable for the expression of SVMPs, unlocking biomedical use in haematology, and discovery of novel snakebite therapeutics.

pharmacology and toxicology↗

bioRxiv2025

Off-Target Structural Insights: ArnA and AcrB in Bacterial Membrane Protein Cryo-EM Analysis

Membrane protein quality control in Escherichia coli involves coordinated actions of the AAA+ protease FtsH, the insertase YidC, and the regulatory complex HflKC. These systems maintain proteostasis by facilitating membrane protein insertion, folding, and degradation. To gain structural insights into a putative complex formed by FtsH and YidC, we performed single-particle cryogenic electron microscopy on detergent-solubilized membrane samples, from which FtsH and YidC were purified using Ni-NTA affinity and size exclusion chromatography. Although SDS-PAGE analysis indicated a high purity of these proteins, cryo-EM datasets unexpectedly yielded high-resolution structures of ArnA and AcrB at 4.0 [A] and 2.9 [A] resolutions, respectivelyArnA is a bifunctional enzyme involved in lipid A modification and polymyxin resistance, while AcrB is a multidrug efflux transporter of the AcrAB-TolC system. ArnA and AcrB are known membrane protein contaminants after Ni-NTA purifications. However, they were also detected in Strep-Tactin affinity purified FtsH-YidC samples. ArnA, typically cytoplasmic, was consistently found in membrane-isolated samples, indicating an association with membrane components. Two-dimensional class averages revealed additional particles resembling GroEL, cytochrome bo oxidase, and the AAA+ cytoplasmic domain of FtsH. Although our preparation was initially considered homogeneous, neither full-size FtsH nor the intact FtsH-YidC complex could be resolved. This case highlights that cryo-EM can reveal structural information beyond the intended target, and that overexpression of membrane proteins involved in quality control may lead to the co-purification of proteins such as ArnA and AcrB.

biochemistry↗

bioRxiv2025

Molecular mechanism for cargo-mediated initiation of kinesin-1 activation

Kinesin-1 is a dynamic heterotetrameric assembly of two heavy and two light chains (KHC and KLC) that mediates microtubule-based intracellular transport of many different cargoes. The complex adopts a compact, autoinhibited state that is activated by cargo-adaptor proteins containing specific short linear peptide motifs (SLiMs). These motifs interact with the tetratricopeptide repeat (TPR) domains of the KLCs. The mechanism coupling SLiM recognition to activation-associated conformational changes in the complex is unknown. Here we combine protein design, computational modelling, biophysical analysis, and electron microscopy to examine the structural and mechanistic consequences of SLiM binding to the KLC-TPR domain within the complete heterotetrameric holoenzyme. We show that coiled coil 1 (CC1) of the KHC docks KLC TPR domains in the autoinhibited complex, forming the shoulder feature observed in electron microscopy. Disrupting this interaction or binding an activating SLiM dislocates the TPR shoulder, freeing the motor domains and promoting transition between its closed, inactive, and open states. Opening the kinesin-1 complex facilitates binding to the microtubule-associated kinesin-1 cofactor, MAP7. Therefore, cargo-mediated dislocation of the TPR shoulder serves as a key initial step in kinesin-1 activation, allosterically linking cargo binding to motor dynamics.

biochemistry↗

bioRxiv2024

Dynamic RNA binding and unfolding by nonsense-mediated mRNA decay factor UPF2

Nonsense-mediated mRNA decay (NMD) is an mRNA surveillance pathway involved in translational control and gene expression regulation. Core NMD factors UPF1, UPF2 and UPF3B are conserved from yeast to humans and essential to target mcRNAs with a premature stop codon for decay. UPF2 binding to UPF1 activates UPF1s ATPase and helicase activities, and UPF2 binding to UPF3B is important for its association with the exon-junction complex and efficient NMD. However, UPF2s association with RNA remains largely uncharacterized. Here, we analyze nucleic acid binding, identifying the first and third MIF4G domains of UPF2 as main RNA-/DNA-binding modules. We find that UPF2s MIF4G domain-3 has RNA annealing activity while full-length UPF2 unfolds our reporter hairpin-RNA structure. We show that UPF2 preferentially binds and stabilizes single-stranded RNA (ss-RNA) in a sequence-independent manner. Concomitant to ss-RNA binding, UPF2 undergoes a distinct conformational change in its otherwise highly dynamic structure. UPF2s RNA binding and unfolding activity may support UPF1s helicase and mRNP remodeling activity and, in combination with UPF3B, stabilize UPF1s association with nonsense mRNA.

biochemistry↗

bioRxiv2023

Allosteric modulation by the fatty acid site in the glycosylated SARS-CoV-2 spike

The trimeric spike protein plays an essential role in the SARS-CoV-2 virus lifecycle, facilitating virus entry through binding to the cellular receptor angiotensin-converting enzyme 2 (ACE2) and mediating viral-host membrane fusion. The SARS-CoV-2 spike contains a fatty acid (FA) binding site at the interface between two neighbouring receptor-binding domains. This site, also found in some other coronaviruses, binds free fatty acids such as linoleic acid. Binding at this site locks the spike in a non-infectious, closed conformation. This site is coupled to functionally important regions, but the effects of glycans on these allosteric effects have not been investigated. Understanding allostery and how this site modulates the behaviour of the spike protein could potentiate the development of promising alternative strategies for new coronavirus therapies. Here, we apply dynamical nonequilibrium molecular dynamics (D-NEMD) simulations to investigate allosteric effects of the FA site in the fully glycosylated spike of the original SARS-CoV-2 ancestral variant. The results show allosteric networks that connect the FA site to important functional regions of the protein, including some more than 40 [A] away, including the receptor binding motif, an antigenic supersite in the N-terminal domain, the furin cleavage site, regions surrounding the fusion peptide, and another allosteric site known to bind heme and biliverdin. The networks identified here highlight the complexity of the allosteric modulation in this protein and reveal a striking and unexpected connection between different allosteric sites. Notably, 65% of amino acid substitutions, deletions and insertions in the Alpha, Beta, Delta, Gamma and Omicron variants map onto or close to the identified allosteric pathways. Comparison of the FA site connections from D-NEMD in the glycosylated and non-glycosylated spikes revealed that the presence of glycans does not qualitatively change the internal allosteric pathways within the protein, with some glycans facilitating the transmission of the structural changes within and between subunits. Significance statementThe spike protein is crucial for the SARS-CoV-2 virus, enabling the fusion of the viral and host cell membranes. This protein contains several allosteric sites, including a fatty acid binding site at the interface between every two neighbouring receptor-binding domains. This site modulates the behaviour of the protein, with the binding of various free fatty acids and other small molecules influencing the spikes structure. In particular, the binding of linoleic acid, an essential fatty acid molecule, stabilizes the protein in a non-infectious locked conformation, thus making it inaccessible for binding to human receptors. Here, we investigate how the fatty acid site modulates the structural and dynamical behaviour of the fully glycosylated protein. Our work reveals complex patterns of communication between the fatty acid site and functionally important regions of the spike (including the receptor binding motif, the antigenic supersite in the N-terminal domain, the heme/biliverdin site, furin cleavage site and the fusion-peptide surrounding regions) and shed new light on the roles of glycans in this protein.

biochemistry↗

bioRxiv2023

Engineering the ADDobody protein scaffold for generation of high-avidity ADDomer super-binders

Adenovirus-derived dodecamer (ADDomer) nanoparticles comprise 60 copies of Adenovirus penton base protein (PBP). ADDomer is thermostable, rendering the storage, transport and deployment of ADDomer-based therapeutics independent of a cold-chain. To expand the scope of ADDomer nanoparticles for new applications, we engineered ADDobodies. ADDobodies represent the crown domain of the PBP, genetically separated from its multimerization domain. We inserted heterologous sequences into hyper-variable loops in the crown domain. The resulting ADDobodies were expressed at high yields in Escherichia coli, are monomeric and maintain thermostability. We solved the X-ray structure of an ADDobody prototype validating our design. We demonstrated that ADDobodies can be used to select a specific binder against a target in in vitro selection experiments using ribosome display, with an enrichment factor of [~]104-fold in one selection round. We show that ADDobodies can be converted back into ADDomers by genetically reconnecting the selected ADDobody with the PBP multimerization domain from a different species, giving rise to a multivalent nanoparticle, called Chimera, confirmed by a 2.2 [A] structure determined by cryogenic electron microscopy (cryo-EM). Chimera comprises 60 binding sites, resulting in ultra-high, picomolar avidity to the target.

synthetic biology↗

bioRxiv2023

Structure of the Commander endosomal trafficking complex linked to X-linked intellectual disability/Ritscher-Schinzel syndrome

The Commander complex is required for endosomal recycling of diverse transmembrane cargos and is mutated in Ritscher-Schinzel syndrome. It comprises two subassemblies; Retriever composed of VPS35L, VPS26C and VPS29, and the CCC complex which contains ten subunits COMMD1-COMMD10 and two coiled-coil domain-containing (CCDC) proteins CCDC22 and CCDC93. Combining X-ray crystallography, electron cryomicroscopy and in silico predictions we have assembled a complete structural model of Commander. Retriever is distantly related to the endosomal Retromer complex but has unique features preventing the shared VPS29 subunit from interacting with Retromer-associated factors. The COMMD proteins form a distinctive hetero-decameric ring stabilised by extensive interactions with CCDC22 and CCDC93. These adopt a coiled-coil structure that connects the CCC and Retriever assemblies and recruits a sixteenth subunit, DENND10, to form the complete Commander complex. The structure allows mapping of disease-causing mutations and reveals the molecular features required for the function of this evolutionarily conserved trafficking machinery.

biochemistry↗

bioRxiv2022

Molecular dynamics of spike variants in the locked conformation: RBD interfaces, fatty acid binding and furin cleavage sites.

Since December 2019 the SARS-CoV-2 virus has infected billions of people around the world and caused millions of deaths. The ability for this RNA virus to mutate has produced variants that have been responsible for waves of infections across the globe. The spike protein on the surface of the SARS-CoV-2 virion is responsible for cell entry in the infection process. Here we have studied the spike proteins from the Original, Alpha (B.1.1.7), Delta (B1.617.2), Delta-plus (B1.617.2-AY1), Omicron BA.1 and Omicron BA.2 variants. Using models built from cryo-EM structures with linoleate bound (6BZ5.pdb) and the N-terminal domain from 7JJI.pdb, each is built from the first residue, with missing loops modelled and 45 disulphides per trimer. Each spike variant was modified from the same Original model framework to maximise comparability. Three replicate, 200 ns atomistic molecular dynamics simulations were performed for each case. (These data also provide the basis for further, non-equilibrium molecular dynamics simulations, published elsewhere.) The analysis of our equilibrium molecular dynamics reveals that sequence variation at the closed receptor binding domain interface particularly for Omicron BA.2 has implications for the avidity of the locked conformation, with potential effects on Omicron BA.1 and Delta-plus. Linoleate binding has a mildly stabilizing effect on furin cleavage site motions in the Original and Alpha variants, but has no effect in Delta, Delta-plus and slightly increases motions at this site for Omicron BA.1, but not BA.2, under these simulation conditions.

biochemistry↗

bioRxiv2022

Molecular architecture of the autoinhibited kinesin-1 lambda particle

Despite continuing progress in kinesin enzyme mechanochemistry and emerging understanding of the cargo recognition machinery, it is not known how these functions are coupled and controlled by the alpha-helical coiled coils encoded by a large component of kinesin protein sequences. Here, we combine computational structure prediction with single-particle negative stain electron microscopy to reveal the coiled-coil architecture of heterotetrameric kinesin-1, in its compact state. An unusual flexion in the scaffold enables folding of the complex, bringing the kinesin heavy chain-light chain interface into close apposition with a tetrameric assembly formed from the region of the molecule previously assumed to be the folding hinge. This framework for autoinhibition is required to uncover how engagement of cargo and other regulatory factors drive kinesin-1 activation. Summary statementIntegration of computational structure prediction with electron microscopy reveals the coiled-coil architecture of the autoinhibited compact conformer of the microtubule motor, kinesin-1.

cell biology↗

bioRxiv2022

SARS-CoV-2 spike variants differ in their allosteric response to linoleic acid

The SARS-CoV-2 spike protein contains a fatty acid binding site, also found in some other coronaviruses (e.g. SARS-CoV), which binds linoleic acid and is functionally important. When occupied by linoleic acid, it reduces infectivity, by locking the spike in a less infectious conformation. Here, we use dynamical-nonequilibrium molecular dynamics (D-NEMD) simulations to compare the response of spike variants to linoleic acid removal. These simulations show that the fatty acid site is coupled to functional regions of the protein, some of them far from the site (e.g. in the receptor-binding motif, N-terminal domain, the furin cleavage site located in position 679-685 and the fusion peptide-surrounding regions) and identify the allosteric networks involved in these connections. Comparison of the response of the original ( Wuhan) spike with four variants: Alpha, Delta, Delta plus and Omicron BA.1 show that the variants differ significantly in their response to linoleic acid removal. The allosteric connections to the fatty acid site on Alpha are generally similar to the original protein, except for the receptor-binding motif and S71-R78 region which show a weaker link to the FA site. In contrast, Omicron is the most affected variant exhibiting significant differences in the receptor-binding motif, N-terminal domain, V622-L629 and the furin cleavage site. These differences in allosteric modulation may be of functional relevance, e.g. in differences in transmissibility and virulence. Experimental comparison of the effects of linoleic acid on different variants is warranted.

biochemistry↗

bioRxiv2022

The Free Fatty Acid-Binding Pocket is a Conserved Hallmark in Pathogenic β-Coronavirus Spike Proteins from SARS-CoV to Omicron

As COVID-19 persists, severe acquired respiratory syndrome coronavirus-2 (SARS-CoV-2) Variants of Concern (VOCs) emerge, accumulating spike (S) glycoprotein mutations. S receptor-binding domain (RBD) comprises a free fatty acid (FFA)-binding pocket. FFA-binding stabilizes a locked S conformation, interfering with virus infectivity. We provide evidence that the pocket is conserved in pathogenic {beta}-coronaviruses ({beta}-CoVs) infecting humans. SARS-CoV, MERS-CoV, SARS-CoV-2 and VOCs bind the essential FFA linoleic acid (LA), while binding is abolished by one mutation in common cold-causing HCoV-HKU1. In the SARS-CoV S structure, LA stabilizes the locked conformation while the open, infectious conformation is LA-free. Electron tomography of SARS-CoV-2 infected cells reveals that LA-treatment inhibits viral replication, resulting in fewer, deformed virions. Our results establish FFA-binding as a hallmark of pathogenic {beta}-CoV infection and replication, highlighting potential antiviral strategies. One-Sentence SummaryFree fatty acid-binding is conserved in pathogenic {beta}-coronavirus S proteins and suppresses viral infection and replication.

biochemistry↗

bioRxiv2022

Molecular basis of neurodevelopmental disorder-causing mutation in nonsense-mediated mRNA decay factor UPF3B

UPF3B is a key nonsense-mediated mRNA decay (NMD) factor required for surveillance of mRNA and regulation of eukaryotic gene expression. Mutations in UPF3B cause intellectual disability. The underlying molecular mechanisms remain unexplored as the mutations lie in an uncharacterized region of UPF3B. Here, we show that UPF3B shares structural and functional homology to the Drosophila Behavior/Human Splicing protein family comprising an RNA-recognition motif-like domain (RRM-L), a NONA/paraspeckle-like domain (NOPS-L), and extended -helical domains essential for ribosome- and RNA-binding and RNA-induced oligomerization. A co-crystal structure of UPF3B with the third middle domain of eukaryotic initiation factor 4G (MIF4GIII) of UPF2 reveals an unexpectedly intimate binding interface. UPF3Bs disease-causing mutation Y160D located in the NOPS-L domain reduces the UPF2 binding affinity ~40-fold compared to wildtype UPF3B. UPF3Bs paralogue UPF3A, an NMD antagonist which is upregulated in patients with the UPF3B-Y160D mutation, binds UPF2 with ~10-fold higher affinity than UPF3B, leading to impaired NMD activity and upregulation of mRNAs involved in neurodevelopment.

biochemistry↗

bioRxiv2021

The fatty acid site is coupled to functional motifs in the SARS-CoV-2 spike protein and modulates spike allosteric behaviour

The SARS-CoV-2 spike protein is the first contact point between the SARS-CoV-2 virus and host cells and mediates membrane fusion. Recently, a fatty acid binding site was identified in the spike (Toelzer et al. Science 2020). The presence of linoleic acid at this site modulates binding of the spike to the human ACE2 receptor, stabilizing a locked conformation of the protein. Here, dynamical-nonequilibrium molecular dynamics simulations reveal that this fatty acid site is coupled to functionally relevant regions of the spike, some of them far from the fatty acid binding pocket. Removal of a ligand from the fatty acid binding site significantly affects the dynamics of distant, functionally important regions of the spike, including the receptor-binding motif, furin cleavage site and fusion-peptide-adjacent regions. The results also show significant differences in behaviour between clinical variants of the spike: e.g. the D614G mutation shows a significantly different conformational response for some structural motifs relevant for binding and fusion. The simulations identify structural networks through which changes at the fatty acid binding site are transmitted within the protein. These communication networks significantly involve positions that are prone to mutation, indicating that observed genetic variation in the spike may alter its response to linoleate binding and associated allosteric communication.

biochemistry↗