A Comparison of Murine Leukemia Viruses That Escape from Human and Rhesus Macaque TRIM5αs

Abstract

To better understand the binding mechanism of TRIM5␣ to retrovirus capsid, we had previously selected N-tropic murine leukemia virus (N-MLV) mutants escaping from rhesus macaque TRIM5␣ (rhTRIM5␣) by passaging the virus in rhTRIM5␣-expressing cells and selecting for nonrestricted variants. To test the commonality of the findings from the rhTRIM5␣ study, we have now employed a similar genetic approach using human TRIM5␣ (huTRIM5␣). Consistent with the rhTRIM5␣ study, the mapped huTRIM5␣ escape mutations were distributed across the capsid exterior, confirming the extended binding surface between virus and restriction factor. Compared to the results of the previous study, fewer escape mutations were identified, with particular mutants being repeatedly selected. Three out four huTRIM5␣ escape variants showed resistance to all primate TRIM5␣s tested, but two of them sacrificed viral fitness, observations that were not made in the rhTRIM5␣ study. Moreover, differences in amino acid changes associated with escape from hu-and rhTRIM5␣s suggested a charge dependence of the restriction by different TRIM5␣s. Taken together, these results suggest that the recognition of the entire capsid surface is a general strategy for TRIM5␣ to restrict MLV but that significantly different specific interactions are involved in the binding of TRIM5␣ from different species to the MLV capsid core. C apsid (CA)-binding retrovirus restriction factors have arisen on at least five occasions in the course of evolution. Their independent evolution is testament to the utility of such factors, either to limit endogenous retrovirus amplification or to inhibit infection by exogenous viruses (1-3). This group of factors includes Fv1 (4, 5), TRIM5␣ (6), and three independently arising hybrid factors, TRIM5CypA1 (7, 8), TRIM5CypA2 (9-12), and TRIM5CypA3 (13) in which a retrotransposed copy of the cellular cyclophilin-A gene has been inserted in the 3= end of the TRIM5 gene. At a minimum, these factors contain a virus CA-binding domain, as well as one or more multimerization domains (14-22).Restriction factor engagement appears to occur soon after retroviral core release into the cell cytoplasm, resulting either in proteasome-mediated CA degradation and an inhibition of reverse transcription (6) or an apparent sequestration of the reverse-transcribed preintegration complex en route to the cell nucleus (23).One of the least-appreciated aspects of restriction by these factors is the ability to restrict multiple species of retrovirus, a property that presumably reflects the ability of these factors to bind several different CA molecules. For example, TRIM5␣ from the cotton-top tamarin can restrict one or more members of the lentivirus, gammaretrovirus, betaretrovirus, and foamy virus genera (24-26), despite extensive differences in the sequences of their CA molecules. Nevertheless, restriction can be sensitive to a single amino acid change, as best characterized by the single change at CA position 110 of murine leukemia virus (MLV) that distinguishes between...

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

“…Alternatively, an intact PRYSPRY domain structure might be required to maintain the structural flexibility of the V1 loop. The flexibility of the V1 loop provides structural plasticity (Biris et al, 2012), conferring upon the PRYSPRY domain the ability to bind different epitopes, in agreement with independent findings suggesting that multiple sites on the capsid are important for recognition by TRIM5α proteins (Kono et al, 2010; Ohkura et al, 2011; Ohkura and Stoye, 2013). Therefore, we think that our PRYSPRY domain variants could be affecting structural plasticity, something that might not be detectable via an ordinary binding assay.…”

Assisted Evolution Enables HIV-1 to Overcome a High TRIM5α-Imposed Genetic Barrier to Rhesus Macaque Tropism

“…These mutations were distributed over several determinants on the surface of the HIV-1 capsid, as has been found in previous studies of retrovirus sensitivity to TRIM5α [40], [41], [44]–[47]. Indeed, although the cyclophilin-binding loop was featured prominently as a site at which mutations conferring decreased HIV-1 sensitivity to rhTRIM5α occurred (positions L83, V86, I91, A92, M96), other determinants included the N-terminal β-hairpin (M10) and helix 6 (G116).…”

“…Indeed, transplantation of SIV mac239 CA in the context of a chimeric HIV-1 confers rhTRIM5α resistance [8], [39]. Similarly, sensitivity or resistance of murine leukemia virus to human TRIM5α can be acquired by mutations in CA [5], [6], [40], [41]. Amino acids in CA that confer TRIM5α sensitivity are generally exposed on the surface of the viral core [42], [43] and are therefore accessible for binding to TRIM5α following viral entry into the cell.…”

Structure of a Spumaretrovirus Gag Central Domain Reveals an Ancient Retroviral Capsid

“…Orthoretrovirus restriction requires interaction of Trim5α with the CA component of Gag in the context of an assembled capsid shell [32, 70] consistent with the genetic mapping within CA of the amino-acid determinants for restriction specificity [71, 72]. It appears that CA-hexamers, the basic building block for core assembly, represent the primary target for Trim5α restriction [73, 74] and a similar picture is emerging for Fv1 [75, 76].…”