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 (TRIM5αrh) 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 TRIM5αrh exhibits 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 TRIM5αrh PRYSPRY 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 TRIM5αrh to the HIV-1 core, to block HIV-1 infection.