A Retroviral Chimeric Capsid Protein Reveals the Role of the N-Terminal beta-Hairpin in Mature Core Assembly

The human immunodeficiency virus (HIV) is an enveloped virus constituted by two monomeric RNA molecules that encode for 15 proteins. Among these are the structural proteins that are translated as the gag polyprotein. In order to become infectious, HIV must undergo a maturation process mediated by the proteolytic cleavage of gag to give rise to the isolated structural protein matrix, capsid (CA), nucleocapsid as well as p6 and spacer peptides 1 and 2. Upon maturation, the 13 N-terminal residues from CA fold into a beta-hairpin, which is stabilized mainly by a salt bridge between Prol and Asp51. Previous reports have shown that non-formation of the salt bridge, which potentially disrupts proper beta-hairpin arrangement, generates noninfectious virus or aberrant cores. To date, however, there is no consensus on the role of the beta-hairpin. In order to shed light in this subject, we have generated mutations in the hairpin region to examine what features would be crucial for the beta-hairpin's role in retroviral mature core formation. These features include the importance of the proline at the N-terminus, the amino acid sequence, and the physical structure of the beta-hairpin itself. The presented experiments provide biochemical evidence that beta-hairpin formation plays an important role in regard to CA protein conformation required to support proper mature core arrangement. Hydrogen/deuterium exchange and in vitro assembly reactions illustrated the importance of the beta-hairpin structure, its dynamics, and its influence on the orientation of helix 1 for the assembly of the mature CA lattice.close11

After grazing exclusion, is there any modification of strategy for two guerrilla species : Elymus repens (L.) Gould and Agrostis stolonifera (L.)?

Elymus repens (L.) Gould and Agrostis stolonifera (L.), are competitive grasses with guerrilla strategy that invade grasslands with a low stocking rate. In this work, we tested the hypotheses that grazing exclusion facilitates vegetative development of rhizomes and stolons of these clonal grasses and that such change is a key mechanism for their abundance in set-aside grasslands. The competitive capacities of these two guerrilla species were characterised by samples in plant community (species richness and biomass) and on the level of individual species (morphometric measurements on stolons and rhizomes) during a growing season. Compared to grasslands where grazing was excluded for three years, species richness was higher in grazed site and the plant community structure differed. Indeed, with grazing exclusion, a shift from annual species with a diversified growth-form to perennial species with a tall tussock and graminoid growth-form was monitored. In ungrazed situation, Elymus repens and Agrostis stolonifera were the dominant grasses, and the standing biomass for the lowland community showed a significant increase compared to the grazed site. Vegetative development increased competitive capacities of these two guerrilla species and led by phenomenon of competitive exclusion to the disappearance of annuals species. With grazing cessation, Elymus repens was found to increase the size of aerial traits (shoot length and the number of leaves per shoot) and this may both be propitious for achieving dominance within plant communities and also maintaining its competitive local advantage. By contrast, Agrostis stolonifera showed an increase in a root trait, i.e. rhizome length, in the fenced site, which provide good ability for spatial propagation and then to explore adjacent patches. We concluded that Elymus repens presented a morphological capacity to change its colonising strategy from a guerrilla strategy to a phalanx strategy, by morphological variability of aerial organs, when it was submitted to competitive stress and environment modifications. Agrostis stolonifera showed a capacity to escape aerial competition resulting from grazing cessation, than to increase underground propagation capacity. The present study highlighted the capacities of Elymus repens to respond in an adaptative way to competitive pressure