Biology subjects

Jemth, P.

Publications and source records attributed to Jemth, P..

17 recordsLinked to original sources

bioRxiv2024

Defining short linear motif binding determinants by phage-based multiplexed deep mutational scanning

Deep mutational scanning (DMS) has emerged as a powerful approach for evaluating the effects of mutations on binding or function. Here, we developed a multiplexed DMS by phage display protocol to define the binding determinants of short linear motifs (SLiMs) binding to peptide binding domains. We first designed a benchmarking DMS library to evaluate the performance of the approach on well-known ligands for eleven different peptide binding domains, including the talin-1 PTB domain. Systematic benchmarking against a gold-standard set of motifs from the eukaryotic linear motif (ELM) database confirmed that the DMS by phage analysis correctly identifies known motif binding determinants. The DMS analysis further defined a non-canonical PTB binding motif, with a putative extended conformation. A second DMS library was designed aiming to provide information on the binding determinants for 19 SLiM-based interactions between human and SARS-CoV-2 proteins. The analysis confirmed the affinity determining residues of viral peptides binding to host proteins, and refined the consensus motifs in human peptides binding to five domains from SARS-CoV-2 proteins, including the non-structural protein (NSP) 9. The DMS analysis further pinpointed mutations that increased the affinity of ligands for NSP3 and NSP9. An affinity improved cell-permeable NSP9-binding peptide was found to exert stronger antiviral effects as compared to the initial wild-type peptide. Our study demonstrates that DMS by phage display can efficiently be multiplexed and applied to refine binding determinants, and shows how DMS by phage display can guide peptide-engineering efforts.

biochemistry↗

bioRxiv2023

Conservation of affinity rather than sequence underlies a dynamic evolution of the motif-mediated p53/MDM2 interaction in teleosts

The transcription factor and cell cycle regulator p53 is marked for degradation by the ubiquitin ligase MDM2. The interaction between these two proteins is mediated by a conserved binding motif in the disordered p53 transactivation domain (p53TAD) and the folded SWIB domain in MDM2. The conserved motif in p53TAD from zebrafish displays a 20-fold weaker interaction with MDM2, compared to the interaction in human and chicken. To investigate this apparent difference, we tracked the molecular evolution of the p53TAD/MDM2 interaction among ray- finned fishes (Actinopterygii), the largest vertebrate clade. Intriguingly, phylogenetic analyses, ancestral sequence reconstructions, and binding experiments showed that different loss-of- affinity changes in the canonical binding motif within p53TAD have occurred repeatedly and convergently in different fish lineages, resulting in relatively low extant affinities (KD = 0.5-5 M). However, for eleven different fish p53TAD/MDM2 interactions, non-conserved regions flanking the canonical motif increased the affinity 4 to 73-fold to be on par with the human interaction. Our findings suggest that compensating changes at conserved and non-conserved positions within the motif, as well as in flanking regions of low conservation, underlie a stabilizing selection of "functional affinity" in the p53TAD/MDM2 interaction. Such interplay complicates bioinformatic prediction of binding and call for experimental validation. Motif- mediated protein-protein interactions involving short binding motifs and folded interaction domains are very common across multicellular life. It is likely that evolution of affinity in motif- mediated interactions often involves an interplay between specific interactions made by conserved motif residues and non-specific interactions by non-conserved disordered regions.

molecular biology↗

bioRxiv2023

Folded alpha helical putative new proteins from Apilactobacillus kunkeei

The emergence of new proteins is a central question in biology. Most tertiary protein folds known to date appear to have an ancient origin, but it is clear from bioinformatic analyses that new proteins continuously emerge in all organismal groups. However, there is a paucity of experimental data on new proteins regarding their structure and biophysical properties. We performed a detailed phylogenetic analysis and identified 48 putative open reading frames in the honeybee-associated bacterium Apilactobacillus kunkeei for which no homologs could be identified in closely-related species, suggesting that they could be relatively new on an evolutionary time scale and represent recently evolved proteins. Using circular dichroism-, fluorescence- and nuclear magnetic resonance spectroscopy we investigated five of these proteins and show that they are not intrinsically disordered, but populate alpha-helical dominated folded states with relatively low thermodynamic stability (0-3 kcal/mol). The data demonstrate that small new proteins readily adopt simple folded conformations suggesting that more complex tertiary structures can be continuously re-invented during evolution by fusion of such simple secondary structure elements. These findings have implications for the general view on protein evolution, where de novo emergence of folded proteins may be a common event.

molecular biology↗

bioRxiv2023

The evolution of binding affinities between p53 and MDM2 across the animal kingdom demonstrates high plasticity in motif-mediated interactions

The interaction between the transcription factor p53 and the ubiquitin ligase MDM2 results in degradation of p53 and is well studied in cancer biology and drug development. Available sequence data suggest that both p53 and MDM2-family proteins are present across the animal kingdom. However, the interacting regions are missing in some animal groups, and it is not clear whether MDM2 interacts with, and regulates p53 in all species. We used phylogenetic analyses and biophysical measurements to examine the evolution of affinity between the interacting protein regions: a conserved 12-residue intrinsically disordered binding motif in the p53 transactivation domain (TAD) and the folded SWIB domain of MDM2. The affinity varied significantly across the animal kingdom. The p53TAD/MDM2 interaction among jawed vertebrates displayed high affinity, in particular for chicken and human proteins (KD around 0.1 M). The affinity of the bay mussel p53TAD/MDM2 complex was lower (KD = 15 M) and those from a placozoan, an arthropod and a jawless vertebrate were very low or non-detectable (KD > 100 M). Binding experiments with reconstructed ancestral p53TAD/MDM2 variants suggested that a micromolar affinity interaction was present in the ancestral bilaterian animal and was later enhanced in tetrapods while lost in other linages. The different evolutionary trajectories of p53TAD/MDM2 affinity during speciation demonstrate high plasticity of motif-mediated interactions and the potential for rapid adaptation of p53 regulation during times of change. Neutral drift in unconstrained disordered regions may underlie the plasticity and explain the observed low sequence conservation in transactivation domains such as p53TAD. Statement for broader audienceThe protein p53 regulates central cellular processes including cell division and programmed cell death. p53 is regulated by another protein, MDM2, which binds to p53 and marks it for destruction. We measured the interaction between present-day and reconstructed ancient p53 and MDM2 proteins and found a range of binding strengths. Our findings suggest that rapid evolution of the p53/MDM2 interaction facilitates adaptation of p53 regulation during speciation.

molecular biology↗

bioRxiv2022

Evaluation of affinity-purification coupled to mass spectrometry approaches for capture of short linear motif-based interactions

Low affinity and transient protein-protein interactions, such as short linear motif (SLiM)-based interactions, require dedicated experimental tools for discovery and validation. Here, we evaluated and compared biotinylated peptide pulldown and protein interaction screen on peptide matrix (PRISMA) coupled to mass-spectrometry (MS) using a set of peptides containing interaction motifs. Eight different peptide sequences that engage in interactions with three distinct protein domains (KEAP1 Kelch, MDM2 SWIB, and TSG101 UEV) with a wide range of affinities were tested. We found that peptide pulldown can be an effective approach for SLiM validation, however, parameters such as protein abundance and competitive interactions can prevent the capture of known interactors. The use of tandem peptide repeats improved the capture and preservation of some interactions. When testing PRISMA, it failed to provide comparable results for a model peptide that successfully pulled down a known interactor using biotinylated peptide pulldown. Overall, in our hands, we find that albeit more laborious, biotin-peptide pulldown was more successful in terms of validation of known interactions. Our results highlight that the tested affinity-capture MS-based methods for validation of SLiM-based interactions from cell lysates are suboptimal, and we identified parameters for consideration for method development.

biochemistry↗

bioRxiv2022

Identification of motif-based interactions between SARS-CoV-2 protein domains and human peptide ligands pinpoint antiviral targets.

The infection and replication cycle of all viruses depend on interactions between viral and host proteins. Each of these protein-protein interactions is therefore a potential drug target. These host-virus interactions often involve a disordered protein region on one side of the interface and a folded protein domain on the other. Here, we used proteomic peptide phage display (ProP-PD) to identify peptides from the intrinsically disordered regions of the human proteome that bind to folded protein domains encoded by the SARS-CoV-2 genome. Eleven folded domains of SARS-CoV-2 proteins were found to bind peptides from human proteins. Of 281 high/medium confidence peptides, 23 interactions involving eight SARS-CoV-2 protein domains were tested by fluorescence polarization, and binding was observed with affinities spanning the whole micromolar range. The key specificity determinants were established for six of these domains, two based on ProP-PD and four by alanine scanning SPOT arrays. Finally, two cell-penetrating peptides, targeting Nsp9 and Nsp16, respectively, were shown to function as inhibitors of viral replication. Our findings demonstrate how high-throughput peptide binding screens simultaneously provide information on potential host-virus interactions and identify ligands with antiviral properties.

molecular biology↗

bioRxiv2022

A syntenin inhibitor blocks endosomal entry of SARS-CoV-2 and a panel of RNA viruses

Viruses are dependent on interactions with host factors in order to efficiently establish an infection and replicate. Targeting such interactions provides an attractive strategy to develop novel antivirals. Syntenin is a protein known to regulate the architecture of cellular membranes by its involvement in protein trafficking, and has previously been shown to be important for HPV infection. Here we show that a highly potent and metabolically stable peptide inhibitor that binds to the PDZ1 domain of syntenin inhibits SARS-CoV-2 infection by blocking the endosomal entry of the virus. Furthermore, we found that the inhibitor also hampered chikungunya infection, and strongly reduced flavivirus infection, which are completely dependent on receptor mediated endocytosis for their entry. In conclusion, we have identified a novel pan-viral inhibitor that efficiently target a broad range of RNA viruses.

biochemistry↗

bioRxiv2022

Large-scale phage-based screening reveals extensive pan-viral mimicry of host short linear motifs

Viruses mimic host short linear motifs (SLiMs) to hijack and deregulate cellular functions. Studies of motif-mediated interactions therefore provide insight into virus-host dependencies, and reveal targets for therapeutic intervention. Here, we describe the pan-viral discovery of 1,712 SLiM-based virus-host interactions using a phage peptidome tiling the intrinsically disordered protein regions of 229 RNA viruses. We find mimicry of host SLiMs to be a ubiquitous viral strategy, reveal novel host proteins hijacked by viruses, and identify cellular pathways frequently deregulated by viral motif mimicry. Using structural and biophysical analyses, we show that viral mimicry-based interactions have similar binding strength and bound conformations as endogenous interactions. Finally, we establish polyadenylate-binding protein 1 as a potential target for broad-spectrum antiviral agent development. Our platform enables rapid discovery of mechanisms of viral interference and the identification of potential therapeutic targets which can aid in combating future epidemics and pandemics.

biochemistry↗

bioRxiv2022

Rescue of Escherichia coli auxotrophy by de novo small proteins

Increasing numbers of small proteins with diverse physiological roles are being identified and characterized in both prokaryotic and eukaryotic systems, but the origins and evolution of these proteins remain unclear. Recent genomic sequence analyses in several organisms suggest that new functions encoded by small open reading frames (sORFs) may emerge de novo from noncoding sequences. However, experimental data demonstrating if and how randomly generated sORFs can confer beneficial effects to cells are limited. Here we show that by up-regulating hisB expression, de novo small proteins ([≤] 50 amino acids in length) selected from random sequence libraries can rescue Escherichia coli cells that lack the conditionally essential SerB enzyme. The recovered small proteins are hydrophobic and confer their rescue effect by binding to the 5 end regulatory region of the his operon mRNA, suggesting that protein binding promotes structural rearrangements of the RNA that allow increased hisB expression. This study adds RNA regulatory elements as another interacting partner for de novo proteins isolated from random sequence libraries, and provides further experimental evidence that small proteins with selective benefits can originate from the expression of nonfunctional sequences.

evolutionary biology↗

bioRxiv2021

The dynamic properties of a nuclear coactivator binding domain are evolutionarily conserved

Evolution of proteins is constrained by their structure and function. While there is a consensus that the plasticity of intrinsically disordered proteins relaxes the structural constraints on evolution there is a paucity of data on the molecular details of these processes. The Nuclear co-activator binding domain (NCBD) from CREB-binding protein is a protein-protein interaction domain, which contains a hydrophobic core but is not behaving as a typical globular domain, and has been desribed as molten-globule like. The highly dynamic properties of NCBD makes it an interesting model system for evolutionary structure-function investigation of intrinsically disordered proteins. We have here compared the structure and biophysical properties of an ancient version of NCBD present in a bilaterian animal ancestor living around 600 million years ago with extant human NCBD. Using a combination of NMR spectroscopy, circular dichroism and kinetic methods we show that although NCBD has increased its thermodynamic stability, it has retained its dynamic biophysical properties in the ligand-free state in the evolutionary lineage leading from the last common bilaterian ancestor to humans. Our findings suggest that the dynamic properties of NCBD have been maintained by purifying selection and thus are important for its function, which includes mediating several distinct protein-protein interactions.

biophysics↗

bioRxiv2021

Large scale discovery of coronavirus-host factor protein interaction motifs reveals SARS-CoV-2 specific mechanisms and vulnerabilities

Viral proteins make extensive use of short peptide interaction motifs to hijack cellular host factors. However, current methods do not identify this important class of protein-protein interactions. Uncovering peptide mediated interactions provides both a molecular understanding of viral interactions with their host and the foundation for developing novel antiviral reagents. Here we describe a scalable viral peptide discovery approach covering 229 RNA viruses that provides high resolution information on direct virus-host interactions. We identify 269 peptide-based interactions for 18 coronaviruses including a specific interaction between the human G3BP1/2 proteins and an {Phi}xFG peptide motif in the SARS-CoV-2 nucleocapsid (N) protein. This interaction supports viral replication and through its {Phi}xFG motif N rewires the G3BP1/2 interactome to disrupt stress granules. A peptide-based inhibitor disrupting the G3BP1/2-N interaction blocks SARS-CoV-2 infection showing that our results can be directly translated into novel specific antiviral reagents.

biochemistry↗

bioRxiv2021

Proteome-scale amino-acid resolution footprinting of protein-binding sites in the intrinsically disordered regions of the human proteome

Specific protein-protein interactions are central to all processes that underlie cell physiology. Numerous studies using a wide range of experimental approaches have identified tens of thousands of human protein-protein interactions. However, many interactions remain to be discovered, and low affinity, conditional and cell type-specific interactions are likely to be disproportionately under-represented. Moreover, for most known protein-protein interactions the binding regions remain uncharacterized. We previously developed proteomic peptide phage display (ProP-PD), a method for simultaneous proteome-scale identification of short linear motif (SLiM)-mediated interactions and footprinting of the binding region with amino acid resolution. Here, we describe the second-generation human disorderome (HD2), an optimized ProP-PD library that tiles all disordered regions of the human proteome and allows the screening of ~1,000,000 overlapping peptides in a single binding assay. We define guidelines for how to process, filter and rank the results and provide PepTools, a toolkit for annotation and analysis of identified hits. We uncovered 2,161 interaction pairs for 35 known SLiM-binding domains and confirmed a subset of 38 interactions by biophysical or cell-based assays. Finally, we show how the amino acid resolution binding site information can be used to pinpoint functionally important disease mutations and phosphorylation events in intrinsically disordered regions of the human proteome. The HD2 ProP-PD library paired with PepTools represents a powerful pipeline for unbiased proteome-wide discovery of SLiM-based interactions.

biochemistry↗

bioRxiv2020

CRISPR/Cas9-based inactivation of human papillomavirus oncogenes E6 and E7 induces senescence in cervical cancer cells

Human papillomaviruses (HPVs) such as HPV16 and HPV18 can cause cancers of the cervix, vagina, vulva, penis, anus and oropharynx. Continuous expression of the HPV viral oncoproteins E6 and E7 are essential for transformation and maintenance of cancer cells. Therefore, therapeutic targeting of E6 and E7 genes can potentially be used to treat HPV-related cancers. Previous CRISPR/Cas9 studies on inactivation of E6 and E7 genes confirmed cell cycle arrest and apoptosis. Here we report that CRISPR/Cas9-based knockout of E6 and E7 can also trigger cellular senescence in HPV18 immortalized HeLa cells. Specifically, HeLa cells in which E6 and E7 were inactivated exhibited characteristic senescence markers like enlarged cell and nucleus surface area, increased {beta}-galactosidase expression, and loss of lamin B1 with detection of cytoplasmic chromatin fragments. Furthermore, the knockout of HPV18 E6 and E7 proteins resulted in upregulation of p53/p21 and pRb/p21 levels in senescent cells. These senescent cells were devoid of characteristic apoptotic markers and re-introduction of codon-modified HPV18 E6 decreased p53 levels. Taken together, our study demonstrates that cellular senescence is as an alternative outcome of HPV oncogene inactivation by the CRISPR/Cas9 methodology.

cancer biology↗

bioRxiv2020

Evolution of an interaction between disordered proteins resulted in increased heterogeneity of the binding transition state

Intrinsically disordered protein (IDP) domains often have multiple binding partners. Little is known regarding molecular changes in the binding mechanism when a new interaction evolves from low to high affinity. Here we compared the degree of native contacts in the transition state of the interaction of two IDP domains, low-affinity ancestral and high-affinity human NCBD and CID. We found that the coupled binding and folding mechanism of the domains is overall similar, but with a higher degree of native hydrophobic contact formation in the transition state of the ancestral complex while more heterogenous transient interactions, including electrostatic, and an increased disorder characterize the human complex. From an evolutionary perspective, adaptation to new binding partners for IDPs may benefit from this ability to exploit multiple alternative transient interactions while retaining the overall pathway.

biophysics↗

bioRxiv2020

Divergent evolution of a protein-protein interaction revealed through ancestral sequence reconstruction and resurrection

The postsynaptic density extends across the postsynaptic dendritic spine with Discs large (DLG) as the most abundant scaffolding protein. DLG dynamically alters the structure of the postsynaptic density, thus controlling the function and distribution of specific receptors at the synapse. PDZ domains make up one of the most abundant protein interaction domain families in animals. One important interaction governing postsynaptic architecture is that between the PDZ3 domain from DLG and cysteine-rich interactor of PDZ3 (CRIPT). However, little is know regarding functional evolution of the PDZ3:CRIPT interaction. Here, we subjected PDZ3 and CRIPT to ancestral sequence reconstruction, resurrection and biophysical experiments. We show that the PDZ3:CRIPT interaction is an ancient interaction, which was present in the last common ancestor of Eukaryotes, and that high affinity is maintained in most extant animal phyla. However, affinity is low in nematodes and insects, raising questions about the physiological function of the interaction in species from these animal groups. Our findings demonstrate how an apparently established protein-protein interaction involved in cellular scaffolding in bilaterians can suddenly be subject to dynamic evolution including possible loss of function.

molecular biology↗

bioRxiv2020

Supertertiary protein structure affects an allosteric network

The notion that protein function is allosterically regulated by structural or dynamic changes in proteins has been extensively investigated in several protein domains in isolation. In particular, PDZ domains have represented a paradigm for these studies, despite providing conflicting results. Furthermore, it is still unknown how the association between protein domains in supramodules, consitituting so-called supertertiary structure, affects allosteric networks. Here, we experimentally mapped the allosteric network in a PDZ:ligand complex, both in isolation and in the context of a supramodular structure, and show that allosteric networks in a PDZ domain are highly dependent on the supertertiary structure in which they are present. This striking sensitivity of allosteric networks to presence of adjacent protein domains is likely a common property of supertertiary structures in proteins. Our findings have general implications for prediction of allosteric networks from primary and tertiary structure and for quantitative descriptions of allostery.

biophysics↗

bioRxiv2019

Helix formation during the coupled binding and folding of intrinsically disordered proteins monitored by synchrotron-radiation circular dichroism spectroscopy

Intrinsically disordered proteins organize interaction networks in the cell in many regulation and signalling processes. These proteins often gain structure upon binding to their target proteins in multi-step reactions involving the formation of both secondary and tertiary structure. To understand the interactions of disordered proteins, we need to understand the mechanisms of these coupled folding and binding reactions. We studied helix formation in the binding of the molten globule-like nuclear coactivator binding domain (NCBD) and the disordered interaction domain from activator of thyroid hormone and retinoid receptors (ACTR). We demonstrate that helix formation in a rapid binding reaction can be followed by stopped flow synchrotron-radiation circular dichroism spectroscopy, and describe the design of such a beamline. Fluorescence-monitored binding experiments of ACTR and NCBD display several kinetic phases including one concentration-independent phase, which is consistent with an intermediate stabilized at high ionic strength. Time resolved circular dichroism experiments show that almost all helicity is formed upon initial association of the proteins, or separated from the encounter complex by only a small energy barrier. Through simulation of mechanistic models, we show that the intermediate observed at high ionic strength likely involves a structural rearrangement with minor overall changes in helicity. Our experiments provide a benchmark for simulations of coupled binding reactions and demonstrate the feasibility of using synchrotron radiation circular dichroism for mechanistic studies of protein-protein interactions.

biophysics↗