A SARS-CoV-2 variant carrying the Spike protein amino acid change D614G has become the most prevalent form in the global pandemic. Dynamic tracking of variant frequencies revealed a recurrent pattern ...of G614 increase at multiple geographic levels: national, regional, and municipal. The shift occurred even in local epidemics where the original D614 form was well established prior to introduction of the G614 variant. The consistency of this pattern was highly statistically significant, suggesting that the G614 variant may have a fitness advantage. We found that the G614 variant grows to a higher titer as pseudotyped virions. In infected individuals, G614 is associated with lower RT-PCR cycle thresholds, suggestive of higher upper respiratory tract viral loads, but not with increased disease severity. These findings illuminate changes important for a mechanistic understanding of the virus and support continuing surveillance of Spike mutations to aid with development of immunological interventions.
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•A SARS-CoV-2 variant with Spike G614 has replaced D614 as the dominant pandemic form•The consistent increase of G614 at regional levels may indicate a fitness advantage•G614 is associated with lower RT PCR Cts, suggestive of higher viral loads in patients•The G614 variant grows to higher titers as pseudotyped virions
Korber et al. present evidence that there are now more SARS-CoV-2 viruses circulating in the human population globally that have the G614 form of the Spike protein versus the D614 form that was originally identified from the first human cases in Wuhan, China. Follow-up studies show that patients infected with G614 shed more viral nucleic acid compared with those with D614, and G614-bearing viruses show significantly higher infectious titers in vitro than their D614 counterparts.
The conformational ensemble of intrinsically disordered proteins, such as α-synuclein, are responsible for their function and malfunction. Misfolding of α-synuclein can lead to neurodegenerative ...diseases, and the ability to study their conformations and those of other intrinsically disordered proteins under varying physiological conditions can be crucial to understanding and preventing pathologies. In contrast to well-folded peptides, a consensus feature of IDPs is their low hydropathy and high charge, which makes their conformations sensitive to pH perturbation. We examine a prominent member of this subset of IDPs, α-synuclein, using a divide-and-conquer scheme that provides enhanced sampling of IDP structural ensembles. We constructed conformational ensembles of α-synuclein under neutral (pH ~ 7) and low (pH ~ 3) pH conditions and compared our results with available information obtained from smFRET, SAXS, and NMR studies. Specifically, α-synuclein has been found to in a more compact state at low pH conditions and the structural changes observed are consistent with those from experiments. We also characterize the conformational and dynamic differences between these ensembles and discussed the implication on promoting pathogenic fibril formation. We find that under low pH conditions, neutralization of negatively charged residues leads to compaction of the C-terminal portion of α-synuclein while internal reorganization allows α-synuclein to maintain its overall end-to-end distance. We also observe different levels of intra-protein interaction between three regions of α-synuclein at varying pH and a shift towards more hydrophilic interactions with decreasing pH.
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•A novel divide-and-conquer computational method to sample IDP at different pH conditions.•Predicted conformational changes upon pH perturbation are shown to be consistent with experiments.•At low pH, neutralization of negatively charged residues leads to compaction of the C-terminal portion of α-synuclein.•Internal reorganization allows α-synuclein to maintain its overall end-to-end distance under both pH conditions.
N-linked glycans are ubiquitous in nature and play key roles in biology. For example, glycosylation of pathogenic proteins is a common immune evasive mechanism, hampering the development of ...successful vaccines. Due to their chemical variability and complex dynamics, an accurate molecular understanding of glycans is still limited by the lack of effective resolution of current experimental approaches. Here, we have developed and implemented a reductive model based on the popular Martini 2.2 coarse-grained force field for the computational study of N-glycosylation. We used the HIV-1 Env as a direct applied example of a highly glycosylated protein. Our results indicate that the model not only reproduces many observables in very good agreement with a fully atomistic force field but also can be extended to study large amount of glycosylation variants, a fundamental property that can aid in the development of drugs and vaccines.
Activation of RAF kinase involves the association of its RAS-binding domain (RBD) and cysteine-rich domain (CRD) with membrane-anchored RAS. However, the overall architecture of the RAS/RBD/CRD ...ternary complex and the orientations of its constituent domains at the membrane remain unclear. Here, we have combined all-atom and coarse-grained molecular dynamics (MD) simulations with experimental data to construct and validate a model of membrane-anchored CRD, and used this as a basis to explore models of membrane-anchored RAS/RBD/CRD complex. First, simulations of the CRD revealed that it anchors to the membrane via insertion of its two hydrophobic loops, which is consistent with our NMR measurements of CRD bound to nanodiscs. Simulations of the CRD in the context of membrane-anchored RAS/RBD then show how CRD association with either RAS or RBD could play an unexpected role in guiding the membrane orientations of RAS/RBD. This finding has implications for the formation of RAS-RAS dimers, as different membrane orientations of RAS expose distinct putative dimerization interfaces.
B cell lymphoma-2-associated X protein (BAX) plays a pivotal role in triggering cell apoptosis by permeabilizing the mitochondrial outer membrane. Contrary to previous findings, recent electron ...microscopy (EM) experiments showed that BAX monomers are able to perturb phospholipid nanodiscs (NDs) by forming lipidic pores. Here, we provide structural and thermodynamic interpretation of such data using multiscale resolution molecular dynamics (MD) simulations. Our results suggest that BAX is able to disrupt the stability, lateral packing and enhance the desorption propensity of the lipids in the ND, resulting in the formation of a stable toroidal-like pore. These findings prompted to re-evaluate the previously reported cryo-EM data to generate an improved reconstruction, thereby allowing for a more accurate localization of BAX in the EM map. We conclude that the reduced stability of the BAX-embedded ND eliminates the necessity of forming active BAX oligomers for its disruption.
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•Molecular dynamics simulations extracts dynamical and structural properties of nanodisc•Wrapping by the apolipoprotein influences lipid packing and stability of nanodisc•Addition of single BAX protein is sufficient to trigger pore formation in nanodisc•Simulation led to improved cryo-EM reconstructions of BAX protein and pore in nanodisc
López et al. analyze the structure and dynamics of lipid nanodiscs, both empty and in complex with pro-apoptotic BAX protein. Information from the computational-derived structures prompted changes in image-processing strategy, which led to quality improvements in cryo-EM reconstructions. Together, these findings provide novel insights on the activity of BAX.
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