An entropic safety catch controls Hepatitis C virus entry and antibody resistance

E1 and E2 (E1E2), the fusion proteins of Hepatitis C Virus (HCV), are unlike that of any other virus yet described, and the detailed molecular mechanisms of HCV entry/fusion remain unknown. Hypervariable region-1 (HVR-1) of E2 is a putative intrinsically disordered protein tail. Here, we demonstrate that HVR-1 has an autoinhibitory function that suppresses the activity of E1E2 on free virions; this is dependent on its conformational entropy. Thus, HVR-1 is akin to a safety catch that prevents premature triggering of E1E2 activity. Crucially, this mechanism is turned off by host receptor interactions at the cell surface to allow entry. Mutations that reduce conformational entropy in HVR-1, or genetic deletion of HVR-1, turn off the safety catch to generate hyper-reactive HCV that exhibits enhanced virus entry but is thermally unstable and acutely sensitive to neutralising antibodies. Therefore, the HVR-1 safety catch controls the efficiency of virus entry and maintains resistance to neutralising antibodies. This discovery provides an explanation for the ability of HCV to persist in the face of continual immune assault and represents a novel regulatory mechanism that is likely to be found in other viral fusion machinery

Quantifying selection acting on a complex trait using allele frequency time series data

When selection is acting on a large genetically diverse population, beneficial alleles increase in frequency. This fact can be used to map quantitative trait loci by sequencing the pooled DNA from the population at consecutive time points and observing allele frequency changes. Here, we present a population genetic method to analyze time series data of allele frequencies from such an experiment. Beginning with a range of proposed evolutionary scenarios, the method measures the consistency of each with the observed frequency changes. Evolutionary theory is utilized to formulate equations of motion for the allele frequencies, following which likelihoods for having observed the sequencing data under each scenario are derived. Comparison of these likelihoods gives an insight into the prevailing dynamics of the system under study. We illustrate the method by quantifying selective effects from an experiment, in which two phenotypically different yeast strains were first crossed and then propagated under heat stress (Parts L, Cubillos FA, Warringer J, et al. [14 co-authors]. 2011. Revealing the genetic structure of a trait by sequencing a population under selection. Genome Res). From these data, we discover that about 6% of polymorphic sites evolve nonneutrally under heat stress conditions, either because of their linkage to beneficial (driver) alleles or because they are drivers themselves. We further identify 44 genomic regions containing one or more candidate driver alleles, quantify their apparent selective advantage, obtain estimates of recombination rates within the regions, and show that the dynamics of the drivers display a strong signature of selection going beyond additive models. Our approach is applicable to study adaptation in a range of systems under different evolutionary pressures

Computational studies of Family A and Family B GPCRs

A full picture of the similarities between Family A and Family B GPCRs (G-protein coupled receptors) has been frustrated by the lack of clear homology between the respective sequences. Here, we review previous computational studies on GPCR dimerization in which the putative dimerization interfaces have been analysed using entropy, the ET (evolutionary trace) method and related methods. The results derived from multiple sequence alignments of Family A subfamilies have been mapped on to the rhodopsin crystal structure using standard alignments. Similarly, the results for the Family B alignments have been mapped on to the rhodopsin crystal structure using the ‘cold-spot’ alignment. For both Family A and Family B GPCRs, the sequence analysis indicates that there are functional sites on essentially all transmembrane helices, consistent with the parallel daisy chain model of GPCR oligomerization in which each GPCR makes interactions with a number of neighbouring GPCRs. The results are not too sensitive to the quality of the alignment. Molecular Dynamics simulations of the activation process within a single transmembrane bundle of the rhodopsin and the β2-adrenergic receptor have been reviewed; the key observation, which is consistent with other computational studies, is that there is a translation and bending of helix 6, which contributes to a significant opening out of the intracellular face of the receptor, as shown in the accompanying movies. The simulations required the application of specific experiment-derived harmonic and half-harmonic distance restraints and so the application of such simulations to Family B GPCRs requires considerable care because of the alignment problem. Thus, in order to address the alignment problem, we have exploited the observation that GCR1, a plant GPCR, has homology with Family A, Family B and Family E GPCRs. The resulting alignment for transmembrane helix 3 is presented

The effective rate of influenza reassortment is limited during human infection

10.1371/journal.ppat.1006203PLoS Pathogens132e100620