To further determine the influence of V1V2 on entry characteristics, we analyzed the SF162 and P3N wt and V1V2-deleted envs for trimer stability

To further determine the influence of V1V2 on entry characteristics, we analyzed the SF162 and P3N wt and V1V2-deleted envs for trimer stability. binding site) which were particularly prone to free virus infectivity loss upon EPZ020411 mutation but maintained infectivity in cell-cell transmission. Of note, V1V2 antibody shielding proved important during both free virus contamination and cell-cell transmission. Conclusions Based on our data we propose a model for V1V2 evolution that centers on cell-cell transmission as a salvage pathway for virus replication. Escape from antibody neutralization may frequently result in V1V2 mutations that reduce free virus infectivity. Cell-cell transmission could provide these escape viruses with sufficiently high replication levels that enable selection of compensatory mutations, thereby restoring free virus infectivity while ensuring antibody escape. Thus, our study highlights the need to factor in cell-cell transmission when considering neutralization escape pathways of HIV-1. Electronic supplementary material The online version of this article (doi:10.1186/s12977-014-0075-y) contains supplementary material, which is available to authorized users. Keywords: HIV, Cell-cell transmission, V1V2, Entry, Neutralization, Antibody escape Background The HIV-1 envelope trimer, consisting of three gp120 C gp41 heterodimers, is responsible for mediating HIV entry into target cells and is the single target of neutralizing antibodies elicited in HIV infected individuals [1,2]. The variable loops 1 and 2 (V1V2) of gp120 are a key component in shaping the envelopes susceptibility to neutralization and have long been known to potently shield the trimer against antibody attack [3-13]. Mutations brought on by antibody escape are regarded as the driving force of the high intra- and inter-patient sequence variation of the V1V2 domain name [14,15]. Despite its seemingly high adaptability, mutations within V1V2 can impair envelope trimer functionality and integrity as the domain name mediates intra- and inter-gp120 subunit interactions at the apex of EPZ020411 the envelope spike [16-18]. Numerous naturally occurring V1V2 mutations as well as deletion of the entire domain were described to either obliterate or strongly reduce virus infectivity [3,9,19-25]. Besides its role for trimer integrity, the V1V2 domain name prevents premature adoption of the CD4-bound trimer conformation [16-18,26,27]. This is EPZ020411 of importance for preserving a metastable trimer structure that upon receptor binding and structural rearrangements provides the energy required to complete the entry process [1,28,29]. Secondly, the closed, non-CD4 brought on trimer conformation secures shielding of neutralization-sensitive domains from antibody attack [3-13]. The epitopes profiting most from V1V2 shielding include the V3 loop, situated beneath V1V2 in the intact trimer, the CD4 binding site and CD4-induced epitopes important for co-receptor binding [3-13]. In summary, the available data show that disturbance of the quaternary orientation of V1V2 and V3 at the spike apex, either due to deletion of V1V2 or mutations within or outside V1V2, result in high increases in neutralization sensitivity to antibodies directed against these epitopes. In parallel, mutations leading to V1V2-induced transitions from a closed to an open trimer configuration EPZ020411 result in reductions of virus entry capacity and trimer stability [3-13,19-25]. Contrasting its role in shielding against neutralizing antibodies, the V1V2 domain name itself is usually a target of the neutralization response. Despite the high genetic variability of V1V2, certain sequence motifs are highly conserved across strains and are targeted by broadly neutralizing antibodies (bnAbs) (reviewed in [30]). These bnAb epitopes, including those of PG9 EPZ020411 Rabbit Polyclonal to CD253 and PG16, CH01 to CH04, and PGT141 to PGT145,.