Binding of the rhesus TRIM5α PRYSPRY domain to capsid is necessary but not sufficient for HIV-1 restriction

The PRYSPRY domain of TRIM5α provides specificity and the capsid recognition motif to retroviral restriction. Restriction of HIV-1 by rhesus TRIM5α (TRIM5α_rh) has been correlated to its ability to bind to the HIV-1 core, suggesting that capsid binding is required for restriction. This work explores whether the PRYSPRY domain of TRIM5α_rhexhibits an additional function besides binding to the HIV-1 core. Using our recently described structure of the PRYSPRY domain, we performed an exhaustive structure-function study of the surface and interior residues of the PRYSPRY domain. Testing retroviral restriction and capsid binding of an extensive collection of 60 TRIM5α_rhPRYSPRY variants revealed that binding is necessary but not sufficient for restriction. In support of this hypothesis, we showed that some human tripartite motif proteins bind the HIV-1 capsid but do not restrict HIV-1 infection, such as human TRIM6 and TRIM34. Overall this work suggested that the PRYSPRY domain serves an unknown function, distinct from the binding of TRIM5α_rhto the HIV-1 core, to block HIV-1 infection.