Convergent structural features of respiratory syncytial virus neutralizing antibodies and plasticity of the site V epitope on prefusion F

Abstract

Respiratory syncytial virus (RSV) is a global public health burden for which no licensed vaccine exists. To aid vaccine development via increased understanding of the protective antibody response to RSV prefusion glycoprotein F (PreF), we performed structural and functional studies using the human neutralizing antibody (nAb) RSB1. The crystal structure of PreF complexed with RSB1 reveals a conformational, pre-fusion specific site V epitope with a unique cross-protomer binding mechanism. We identify shared structural features between nAbs RSB1 and CR9501, elucidating for the first time how diverse germlines obtained from different subjects can develop convergent molecular mechanisms for recognition of the same PreF site of vulnerability. Importantly, RSB1-like nAbs were induced upon immunization with PreF in naturally-primed cattle. Together, this work reveals new details underlying the immunogenicity of site V and further supports PreF-based vaccine development efforts.

Improved epitope resolution of the prefusion trimer-specific antibody AM14 bound to the RSV F glycoprotein

“…Our study highlights the reorientation of Arg429 when PreF is bound by either AM14 or 101F. This side-chain flexibility is comparable to that seen when RSV PreF is bound by antibodies RSB1 or CR9501, which each recognizes antigenic site V. 26 In the case of these antibodies, the Lys65 side chain on PreF can assume different conformations in order to be positioned at the interface of the heavy- and light-chain CDRs for either antibody, while Lys87, Glu66, and Asn63 are also significantly displaced in the antibody-bound states. Additionally, CR9501 appears to “splay open” the PreF trimer, suggesting an “induced fit” mechanism for antibody binding.…”

“…Un-tagged DS-Cav1 was produced in Chinese hamster ovary cells and purified by ion exchange and size exclusion chromatography, as previously reported. 26 Fab AM14 was expressed with a Strep Tag II at the heavy-chain C terminus and purified using a StrepTrap HP column (GE Healthcare). The tag was proteolytically cleaved using TEV protease (AcTEV protease, Thermo Fisher Scientific) prior to size exclusion chromatography.…”

“…The AM14 epitope is sandwiched between antigenic sites IV and V, and thus competition with 101F (site IV) as well as RSB1 (site V) has been reported. 26 In order to better understand the footprint of the AM14 epitope as it relates to the epitopes for these surrounding mAbs, and thus elucidate the molecular basis for AM14 competition across multiple antigenic sites, we superimposed our DS-Cav1-AM14 structure with the RSB1 complex (PDB 6W52), the D25 complex (PDB 4JHW), and the 101F-17-mer X-ray structure (PDB 3O45) (Figure 6). The AM14 and 101F epitopes overlap significantly around residues 427-432, which are located on sheet β17 and the loop connecting β17 and β18, as also reported previously, 28 which thus explains the strong binding competition between these antibodies.…”

“…Glycans are shown as sticks and were modeled using the Glyprot server. 64 *Harshbarger et. al., 2020.…”

Cross-protective antibodies against common endemic respiratory viruses

“…Although D25 had greater neutralizing potency against RSV-A (Fig. 3d ), D25 reportedly has weaker potency against some strains of RSV-B and does not neutralize HMPV 36 – 38 . MxR and MPE8 had similar potency in neutralizing both RSV subtypes A and B.…”