Phase Diagram of alpha-Helical and beta-Sheet Forming Peptides

The intrinsic property of proteins to form structural motifs such as alpha-helices and beta-sheets leads to a complex phase behavior in which proteins can assemble into various types of aggregates including crystals, liquidlike phases of unfolded or natively folded proteins, and amyloid fibrils. Here we use a coarse-grained protein model that enables us to perform Monte Carlo simulations for determining the phase diagram of natively folded alpha-helical and unfolded beta-sheet forming peptides. The simulations reveal the existence of various metastable peptide phases. The liquidlike phases are metastable with respect to the fibrillar phases, and there is a hierarchy of metastability

Potential functions of LEA proteins from the brine shrimp Artemia franciscana - Anhydrobiosis meets bioinformatics.

Late embryogenesis abundant (LEA) proteins are a large group of anhydrobiosis-associated intrinsically disordered proteins (IDP), which are commonly found in plants and some animals. The brine shrimp Artemiafranciscana is the only known animal that expresses LEA proteins from three, and not only one, different groups in its anhydrobiotic life stage. The reason for the higher complexity in the A. franciscana LEA proteome (LEAome), compared with other anhydrobiotic animals, remains mostly unknown. To address this issue, we have employed a suite of bioinformatics tools to evaluate the disorder status of the ArtemiaLEAome and to analyze the roles of intrinsic disorder in functioning of brine shrimp LEA proteins. We show here that A. franciscanaLEA proteins from different groups are more similar to each other than one originally expected, while functional differences among members of group 3 are possibly larger than commonly anticipated. Our data show that although these proteins are characterized by a large variety of forms and possible functions, as a general strategy, A. franciscana utilizes glassy matrix forming LEAs concurrently with proteins that more readily interact with binding partners. It is likely that the function(s) of both types, the matrix-forming and partner-binding LEA proteins, are regulated by changing water availability during desiccation

Phenotypic suppression caused by resonance with light-dark cycles indicates the presence of a 24-hours oscillator in yeast and suggests a new role of intrinsically disordered protein regions as internal mediators

The mutual interaction between environment and life is a main topic of biological sciences. An interesting aspect of this interaction is the existence of biological rhythms spanning all the levels of organisms from bacteria to humans. On the other hand, the existence of a coupling between external oscillatory stimuli and adaptation and evolution rate of biological systems is a still unexplored issue. Here we give the demonstration of a substantial increase of heritable phenotypic changes in yeast, an organism lacking a photoreception system, when growing at 12 h light/dark cycles, with respect to both stable dark (or light) or non-12 + 12 h cycling. The model system was a yeast strain lacking a gene whose product is at the crossroad of many different physiological regulations, so ruling out any simple explanation in terms of increase in reverse gene mutations. The abundance of intrinsically disordered protein regions (IDPRs) in both deleted gene product and in its vast ensemble of interactors supports the hypothesis that resonance with the environmental cycle might be mediated by intrinsic disorder-driven interactions of protein molecules. This result opens to the speculation of the effect of environment/biological resonance phenomena in evolution and of the role of protein intrinsically disordered regions as internal mediators. Communicated by Ramaswamy H. Sarma

Effects of Molecular Crowding on stretching of polymers in poor solvent

We consider a linear polymer chain in a disordered environment modeled by percolation clusters on a square lattice. The disordered environment is meant to roughly represent molecular crowding as seen in cells. The model may be viewed as the simplest representation of biopolymers in a cell. We show the existence of intermediate states during stretching arising as a consequence of molecular crowding. In the constant distance ensemble the force-extension curves exhibit oscillations. We observe the emergence of two or more peaks in the probability distribution curves signaling the coexistence of different states and indicating that the transition is discontinuous unlike what is observed in the absence of molecular crowding.Comment: 14 pages, 6 figure

Disease-Associated Mutations Disrupt Functionally Important Regions of Intrinsic Protein Disorder

The effects of disease mutations on protein structure and function have been extensively investigated, and many predictors of the functional impact of single amino acid substitutions are publicly available. The majority of these predictors are based on protein structure and evolutionary conservation, following the assumption that disease mutations predominantly affect folded and conserved protein regions. However, the prevalence of the intrinsically disordered proteins (IDPs) and regions (IDRs) in the human proteome together with their lack of fixed structure and low sequence conservation raise a question about the impact of disease mutations in IDRs. Here, we investigate annotated missense disease mutations and show that 21.7% of them are located within such intrinsically disordered regions. We further demonstrate that 20% of disease mutations in IDRs cause local disorder-to-order transitions, which represents a 1.7–2.7 fold increase compared to annotated polymorphisms and neutral evolutionary substitutions, respectively. Secondary structure predictions show elevated rates of transition from helices and strands into loops and vice versa in the disease mutations dataset. Disease disorder-to-order mutations also influence predicted molecular recognition features (MoRFs) more often than the control mutations. The repertoire of disorder-to-order transition mutations is limited, with five most frequent mutations (R→W, R→C, E→K, R→H, R→Q) collectively accounting for 44% of all deleterious disorder-to-order transitions. As a proof of concept, we performed accelerated molecular dynamics simulations on a deleterious disorder-to-order transition mutation of tumor protein p63 and, in agreement with our predictions, observed an increased α-helical propensity of the region harboring the mutation. Our findings highlight the importance of mutations in IDRs and refine the traditional structure-centric view of disease mutations. The results of this study offer a new perspective on the role of mutations in disease, with implications for improving predictors of the functional impact of missense mutations

Tudor staphylococcal nuclease is a docking platform for stress granule components and is essential for SnRK1 activation in Arabidopsis

Tudor staphylococcal nuclease (TSN; also known as Tudor-SN, p100, or SND1) is a multifunctional, evolutionarily conserved regulator of gene expression, exhibiting cytoprotective activity in animals and plants and oncogenic activity in mammals. During stress, TSN stably associates with stress granules (SGs), in a poorly understood process. Here, we show that in the model plant Arabidopsis thaliana, TSN is an intrinsically disordered protein (IDP) acting as a scaffold for a large pool of other IDPs, enriched for conserved stress granule components as well as novel or plant-specific SG-localized proteins. While approximately 30% of TSN interactors are recruited to stress granules de novo upon stress perception, 70% form a protein-protein interaction network present before the onset of stress. Finally, we demonstrate that TSN and stress granule formation promote heat-induced activation of the evolutionarily conserved energy-sensing SNF1-related protein kinase 1 (SnRK1), the plant orthologue of mammalian AMP-activated protein kinase (AMPK). Our results establish TSN as a docking platform for stress granule proteins, with an important role in stress signalling

Inherent Structural Disorder and Dimerisation of Murine Norovirus NS1-2 Protein

Human noroviruses are highly infectious viruses that cause the majority of acute, non-bacterial epidemic gastroenteritis cases worldwide. The first open reading frame of the norovirus RNA genome encodes for a polyprotein that is cleaved by the viral protease into six non-structural proteins. The first non-structural protein, NS1-2, lacks any significant sequence similarity to other viral or cellular proteins and limited information is available about the function and biophysical characteristics of this protein. Bioinformatic analyses identified an inherently disordered region (residues 1–142) in the highly divergent N-terminal region of the norovirus NS1-2 protein. Expression and purification of the NS1-2 protein of Murine norovirus confirmed these predictions by identifying several features typical of an inherently disordered protein. These were a biased amino acid composition with enrichment in the disorder promoting residues serine and proline, a lack of predicted secondary structure, a hydrophilic nature, an aberrant electrophoretic migration, an increased Stokes radius similar to that predicted for a protein from the pre-molten globule family, a high sensitivity to thermolysin proteolysis and a circular dichroism spectrum typical of an inherently disordered protein. The purification of the NS1-2 protein also identified the presence of an NS1-2 dimer in Escherichia coli and transfected HEK293T cells. Inherent disorder provides significant advantages including structural flexibility and the ability to bind to numerous targets allowing a single protein to have multiple functions. These advantages combined with the potential functional advantages of multimerisation suggest a multi-functional role for the NS1-2 protein

Folding of poly-amino acids and intrinsically disordered proteins in overcrowded milieu induced by pH change

pH-induced structural changes of the synthetic homopolypeptides poly-E, poly-K, poly-R, and intrinsically disordered proteins (IDPs) prothymosin alpha (ProT alpha) and linker histone H1, in concentrated PEG solutions simulating macromolecular crowding conditions within the membrane-less organelles, were characterized. The conformational transitions of the studied poly-amino acids in the concentrated PEG solutions depend on the polymerization degree of these homopolypeptides, the size of their side chains, the charge distribution of the side chains, and the crowding agent concentration. The results obtained for poly-amino acids are valid for IDPs having a significant total charge. The overcrowded conditions promote a significant increase in the cooperativity of the pH-induced coil-alpha-helix transition of ProTa and provoke histone H1 aggregation. The most favorable conditions for the pH-induced structural transitions in concentrated PEG solutions are realized when the charged residues are grouped in blocks, and when the distance between the end of the side group carrying charge and the backbone is small. Therefore, the block-wise distribution of charged residues within the IDPs not only plays an important role in the liquid-liquid phase transitions, but may also define the expressivity of structural transitions of these proteins in the overcrowded conditions of the membrane-less organelles. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Binding of LcrV protein from 'Yersinia pestis' to human T-cells induces apoptosis, which is completely blocked by specific antibodies

The V antigen (LcrV) of the plague bacterium Yersinia pestis is a potent protective protein that is considered as a vaccine component for humans. LcrV mediates the delivery of Yop toxins into host cells and upregulates TLR2-dependent IL-10 production. Although LcrV can interact with the receptor-bound human interferon-γ (hIFN-γ), the significance of these interactions in plague pathogenesis is not known. In this study, we determined the parameters of specific interactions of LcrV and LcrV68–326 with primary human thymocytes and Jurkat T-leukemia cells in the presence of receptor-bound hIFN-γ. Although the C-terminal region of hIFN-γ contains a GRRA138–141 site needed for high-affinity binding of LcrV and LcrV68–326, in the hIFN-γ homodimer, these GRRA138–141 target sites becomes accessible for targeting by LcrV or LcrV68–326 only after immobilization of the hIFN-γ homodimer on the hIFN-γ receptors of thymocytes or Jurkat T-cells. The interaction of LcrV or LcrV68–326 with receptor-bound hIFN-γ on the thymocytes or Jurkat T-cells caused apoptosis of both cell types, which can be completely blocked by the addition of monoclonal antibodies specific to the LEEL32–35 and DEEI203–206 sites of LcrV. The ability of LcrV to utilize hIFN-γ is insidious and may account in part for the severe symptoms of plague in humans