Intrinsically disordered proteins drive membrane curvature.
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ABSTRACT:
SUBMITTER: Busch DJ
PROVIDER: S-EPMC4515776 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Membrane curvature is essential to diverse cellular functions. While classically attributed to structured domains, recent work illustrates that intrinsically disordered proteins are also potent drivers of membrane bending. Specifically, repulsive interactions among disordered domains drive convex bending, while attractive interactions drive concave bending, creating membrane-bound, liquid-like condensates. How might disordered domains that contain both repulsive and attractive domains affect curvature? Here, we examined chimeras that combined attractive and repulsive interactions. When the attractive domain was closer to the membrane, its condensation amplified steric pressure among repulsive domains, leading to convex curvature. In contrast, when the repulsive domain was closer to the membrane, attractive interactions dominated, resulting in concave curvature. Further, a transition from convex to concave curvature occurred with increasing ionic strength, which reduced repulsion while enhancing condensation. In agreement with a simple mechanical model, these results illustrate a set of design rules for membrane bending by disordered proteins.
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Project description:The broad family of LEA proteins are intrinsically disordered proteins (IDPs) with several potential roles in desiccation tolerance, or anhydrobiosis, one of which is to limit desiccation-induced aggregation of cellular proteins. We show here that this activity, termed molecular shield function, is distinct from that of a classical molecular chaperone, such as HSP70 - while HSP70 reduces aggregation of citrate synthase (CS) on heating, two LEA proteins, a nematode group 3 protein, AavLEA1, and a plant group 1 protein, Em, do not; conversely, the LEA proteins reduce CS aggregation on desiccation, while HSP70 lacks this ability. There are also differences in interaction with client proteins - HSP70 can be co-immunoprecipitated with a polyglutamine-containing client, consistent with tight complex formation, whereas the LEA proteins can not, although a loose interaction is observed by Förster resonance energy transfer. In a further exploration of molecular shield function, we demonstrate that synthetic polysaccharides, like LEA proteins, are able to reduce desiccation-induced aggregation of a water-soluble proteome, consistent with a steric interference model of anti-aggregation activity. If molecular shields operate by reducing intermolecular cohesion rates, they should not protect against intramolecular protein damage. This was tested using the monomeric red fluorescent protein, mCherry, which does not undergo aggregation on drying, but the absorbance and emission spectra of its intrinsic fluorophore are dramatically reduced, indicative of intramolecular conformational changes. As expected, these changes are not prevented by AavLEA1, except for a slight protection at high molar ratios, and an AavLEA1-mCherry fusion protein is damaged to the same extent as mCherry alone. A recent hypothesis proposed that proteomes from desiccation-tolerant species contain a higher degree of disorder than intolerant examples, and that this might provide greater intrinsic stability, but a bioinformatics survey does not support this, since there are no significant differences in the degree of disorder between desiccation tolerant and intolerant species. It seems clear therefore that molecular shield function is largely an intermolecular activity implemented by specialist IDPs, distinct from molecular chaperones, but with a role in proteostasis.
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Project description:Frequently elusive to experimental characterizations, intrinsically disordered proteins (IDPs) can be probed using molecular dynamics to provide detailed insight into their complex structure, dynamics, and function. However, previous computational studies were often found to disagree with experiment due to either force field biases or insufficient sampling. In this study, nine unstructured short peptides and the HIV-1 Rev protein were simulated and extended to microseconds to assess these limitations in IDP simulations. In short peptide simulations, a tested IDP-specific force field ff14IDPSFF outperforms its generic counterpart ff14SB as agreement of simulated NMR observables with experiment improves, though its advantages are not clear-cut in apo Rev simulations. It is worth noting that sampling is probably still not sufficient in the ff14SB simulations of apo Rev even if 10 ms have been collected. This indicates that enhanced sampling techniques would greatly benefit IDP simulations. Finally, detailed structural analyses of apo Rev conformations demonstrate different secondary structural preferences between ff14SB (helical) and ff14IDPSFF (random coil). A natural next step is to ask a more quantitative question: whether ff14SB is too ordered or ff14IDPSFF is too disordered in simulations of more complex IDPs such as Rev. This requires further quantitative analyses both experimentally and computationally.
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Project description:BackgroundProteins are composed of one or more amino acid chains and exhibit several structure levels. IDPs (intrinsically disordered proteins) represent a class of proteins that do not fold into any particular conformation and exist as dynamic ensembles in their native state. Due to their intrinsic adaptability, IDPs participate in many regulatory biological processes, including parasite immune escape. Using the information from trypanosomatids proteomes, we developed a pipeline for the identification, characterization and analysis of IDPs. The pipeline employs six disorder prediction methodologies and integrates structural and functional annotation information, subcellular location prediction and physicochemical properties. At the core of the IDP pipeline, there is a relational database that describes the protein disorder knowledge in a logically consistent manner.ResultsThe results obtained from the IDP pipeline showed that Leishmania and Trypanosoma species have approximately 70% and 55% IDPs, respectively. Our results indicate that IDPs in trypanosomatids contain disorder-promoting amino acids and order-promoting amino acids. The functional annotation analysis demonstrated enrichment of selected Gene Ontology terms. A relevant association was observed between the disordered residue numbers within predicted IDPs and their subcellular location, lack of transmembrane domains and lack of predicted function. We validated our computational findings with 2D electrophoresis designed for IDP identification and found that 100% of the identified protein spots were predicted in silico.ConclusionsBecause there is no pipeline or database addressing IDPs in trypanosomatids, the pipeline described here represents the first attempt to establish possible correlations between protein function and structural disorder in these eukaryotes. Interestingly, all significant associations detected in the contingency analysis were observed when the protein disorder content reached approximately 40%. The exploratory data analysis allowed us to develop hypotheses regarding the IDPs' association with key biological features of these parasites, including transcription and transcriptional regulation, RNA processing and splicing, and cytoskeleton.
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