All Three Variable Regions of the TRIM5α B30.2 Domain Can Contribute to the Specificity of Retrovirus Restriction

Abstract

Recent studies have revealed the contribution of TRIM5␣ to retrovirus restriction in cells from a variety of primate species. TRIM5␣ consists of a tripartite motif (the RBCC domain) followed by a B30.2 domain. The B30.2 domain is thought to be involved in determination of restriction specificity and contains three variable regions. To investigate the relationship between the phylogeny of primate TRIM5␣ and retrovirus restriction specificity, a series of chimeric TRIM5␣ consisting of the human RBCC domain followed by the B30.2 domain from various primates was constructed. These constructs showed restriction profiles largely consistent with the origin of the B30.2 domain. Restriction specificity was further investigated with a variety of TRIM5␣s containing mixed or mutated B30.2 domains. This study revealed the importance of all three variable regions for determining restriction specificity. Based on the molecular structures of other PRYSPRY domains solved recently, a model for the molecular structure of the B30.2 domain of TRIM5␣ was developed. The model revealed that the variable regions of the B30.2 domain are present as loops located on one side of the B30.2 core structure. It is hypothesized that these three loops form a binding surface for virus and that evolutionary changes in any one of the loops can alter restriction specificity.Numerous mammalian species have been shown to possess restriction systems that protect against retroviral infection. One example of such an intrinsic restriction factor is Fv1. Mice that carry the Fv1 n allele are resistant to B-tropic murine leukemia virus (B-MLV) infection, whereas mice that have a Fv1 b allele are resistant to N-tropic MLV (N-MLV) infection (20,30,51). The Fv1 gene product interacts with the capsid (CA) protein of incoming MLV, where a single amino acid at position 110 plays a crucial role in the interaction (29). Restriction can be overcome by viral challenge at a high multiplicity of infection, a phenomenon called abrogation (3,11,15,58). We have previously shown that Fv1 shares about 60% amino acid sequence identity with the gag gene of a human endogenous retrovirus (HERV-L) (7), suggesting that Fv1 could be derived from a member of the mouse endogenous retrovirus MERV-L family (4, 7). It seems likely that Fv1 was selected by its capacity to protect mice from exogenous viral infection.In primate cells, several cellular factors participate in the life cycle of retroviruses. The class of factors known to block retroviruses in primate cells includes Lv1 and Ref1. The Lv1 and Ref1 factors can restrict lentiviruses in nonhuman primate cells and N-MLV in human cells, respectively (5,6,13,21,34,57). Extensive efforts to characterize Lv1 and Ref1 resulted in the identification of TRIM5␣ as the principal contributor to both Lv1 and Ref1 activity (22,26,53,63). Rhesus macaque TRIM5␣ (rhTRIM5␣) was shown to restrict human immunodeficiency virus type 1 (HIV-1), whereas its human orthologue (huTRIM5␣) did not (53). Both orthologues were, however, capable of restricting N...

Structural insight into HIV-1 capsid recognition by rhesus TRIM5α

“…In contrast, V1-V3 of PRY/SPRY rh do not fall into either group, and V1 is significantly longer. These findings reinforce the notion that the variable regions of TRIM5α PRY/SPRY are mostly flexible and have evolved for antiviral activity (29)(30)(31).…”

The structural biology of HIV assembly

“…TRIM5α restriction is species-and virus-specific, and the specificity of restriction is largely determined by interactions between the C-terminal SPRY/B30.2 domain and the intact retroviral capsid. Although structural details are still lacking, mutational studies and sequence analyses of different SPRY alleles have provided insights into the determinants of capsid recognition (e.g., see [138][139][140][141]). In TRIM-Cyp, the SPRY domain of TRIM5α is replaced by cyclophilin A (CypA), a well-known peptidyl prolyl isomerase.…”

Generation of human TRIM5α mutants with high HIV-1 restriction activity

“…Construction of chimeric genes in which these three variable regions are swapped between TRIM5a orthologues showed that all three of them can potentially contribute to restriction specificity. 32 Particular attention has been given to the v1 region, which is rich in positively (that is, non-randomly) selected aminoacids. 33,34 Versions of human TRIM5a in which short stretches of the v1 region were replaced by those of the macaque orthologue showed restriction activity against HIV-1.…”