A natural variability in the proline-rich motif of Nef modulates HIV-1 replication in primary T cells

In the infected host, the Nef protein of HIV/SIV is required for high viral loads and thus disease progression [1-3]. Recent evidence indicates that N ef enhances replication in the T cell compartment after the virus is transm itted from dendritic cells (DC) [4]. The underlying mechanism, however, is not clear. Here, we report that a natural variability in the proline-rich m otif (R71T) profoundly modulated Nef-stimulated viral replication in primar y T cells of immature dendritic cell/T cell cocultures. Whereas both Nef va riants (R/T-Nef) downregulated CD4, only the isoform supporting viral repli cation (R-Nef) efficiently interacted with signaling molecules of the T cel l receptor (TCR) environment and stimulated cellular activation. Structural analysis suggested that the R to T conversion induces conformational chang es, altering the flexibility of the loop containing the PxxP motif and henc e its ability to bind cellular partners. Our report suggests that functiona lly and conformationally distinct Nef isoforms modulate HIV replication on the interaction level with the TCR-signaling environment once the virus ent ers the T cell compartment.