A single residue within the V5 region of HIV-1 envelope facilitates viral escape from the broadly neutralizing monoclonal antibody VRC01.

VRC01, a broadly neutralizing monoclonal antibody, is capable of neutralizing a diverse array of HIV-1 isolates by mimicking CD4 binding with the envelope glycoprotein gp120. Nonetheless, resistant strains have been identified. Here, we examined two genetically related and two unrelated envelope clones, derived from CRF08_BC-infected patients, with distinct VRC01 neutralization profiles. A total of 22 chimeric envelope clones was generated by interchanging the loop D and/or V5 regions between the original envelopes or by single alanine substitutions within each region. Analysis of pseudoviruses built from these mutant envelopes showed that interchanging the V5 region between the genetically related or unrelated clones completely swapped their VRC01 sensitivity profiles. Mutagenesis analysis revealed that the asparagine residue at position 460 (Asn-460), a potential N-linked glycosylation site in the V5 region, is a key factor for observed resistance in these strains, which is further supported by our structural modeling. Moreover, changes in resistance were found to positively correlate with deviations in VRC01 binding affinity. Overall, our study indicates that Asn-460 in the V5 region is a critical determinant of sensitivity to VRC01 specifically in these viral strains. The long side chain of Asn-460, and potential glycosylation, may create steric hindrance that lowers binding affinity, thereby increasing resistance to VRC01 neutralization.

Structure of MERS-CoV spike receptor-binding domain complexed with human receptor DPP4.

The spike glycoprotein (S) of recently identified Middle East respiratory syndrome coronavirus (MERS-CoV) targets the cellular receptor, dipeptidyl peptidase 4 (DPP4). Sequence comparison and modeling analysis have revealed a putative receptor-binding domain (RBD) on the viral spike, which mediates this interaction. We report the 3.0 Å-resolution crystal structure of MERS-CoV RBD bound to the extracellular domain of human DPP4. Our results show that MERS-CoV RBD consists of a core and a receptor-binding subdomain. The receptor-binding subdomain interacts with DPP4 ß-propeller but not its intrinsic hydrolase domain. MERS-CoV RBD and related SARS-CoV RBD share a high degree of structural similarity in their core subdomains, but are notably divergent in the receptor-binding subdomain. Mutagenesis studies have identified several key residues in the receptor-binding subdomain that are critical for viral binding to DPP4 and entry into the target cell. The atomic details at the interface between MERS-CoV RBD and DPP4 provide structural understanding of the virus and receptor interaction, which can guide development of therapeutics and vaccines against MERS-CoV infection.