Chimeric nectin1-poliovirus receptor molecules identify a nectin1 region functional in herpes simplex virus entry

Human nectin1 (hNectin1), an adhesion molecule belonging to the nectin fami ly of the immunoglobulin superfamily, mediates entry of herpes simplex viru s (HSV) into cells. The hNectin1 domain that mediates virus entry into cell s and also binds glycoprotein D (gD) has been localized to the first N-term inal V-type domain. The poliovirus receptor (PVR) is a structural homolog t o nectins, but it cannot function as an HSV entry receptor. hNectin1-PVR ch imeras were constructed to functionally locate the site on hNectin1 involve d in HSV entry (HSV entry site). The epitope recognized by monoclonal antib ody (MAb) R1.302, which is able to block HSV entry, was also located. The c himeric receptors were designed to preserve the overall structure of the V domain. The HSV entry activity mapped entirely to the hNectin1 portion loca ted between residues 64 and 94 (64-94), likely to encode the C, C', and C" beta -strands and intervening loops. In turn, this site consisted of two po rtions: one with low-level basal activity for HSV entry (77-94), and one im mediately upstream (residues 64 to 76) which greatly enhanced the HSV entry activity of the downstream region. The gD-binding site mapped substantiall y to the same site, whereas the MAb R1.302 epitope also required a further downstream portion (95-102). The involvement of the 64-76 portion is at dif ference with previous indirect mapping results that were based on competiti ve binding studies (C. Krummenacher et al., J. Virol. 74:10863-10872, 2000) . The A, A', B, D, E, F, and G beta -strands and intervening loops did not appear to play any role in HSV entry. According to the predicted three-dime nsional structure of PVR, the C C' C" site is located peripherally in the V domain and very likely represents an accessible portion at the cell surfac e.