Characterization of a core fragment of the rhesus monkey TRIM5α protein

Here, we express and characterize a protease-resistant 29-kD core fragment containing the B-box 2, coiled coil and adjacent linker (L2) region of TRIM5α. This BCCL2 protein formed dimers and higher-order oligomers in solution. Approximately 40% of the BCCL2 secondary structure consisted of alpha helices. Partial loss of alpha-helical content and dissociation of dimers occurred at 42°C, with the residual alpha helices remaining stable up to 80°C.These results indicate that the B-box 2, coiled-coil and linker 2 regions of TRIM5α form a core dimerization motif that exhibits a high level of alpha-helical content.Soon after entry into the cells of certain mammalian species, some retroviruses encounter blocks mediated by the restriction factor TRIM5α. For example, human immunodeficiency virus (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS), can infect human and chimpanzee cells, but is blocked in cells of Old World monkeys [1-5]. In contrast, simian immunodeficiency virus (SIVmac) infects Old World monkey cells but is restricted in the cells of most New World monkeys [3,6]. TRIM5α, a member of the tripartite motif (TRIM) family of proteins, mediates these early infection blocks [7-12]. Differences in TRIM5α proteins among species account for the distinct patterns of retroviral restriction observed in mammalian lineages [5,7-12]. TRIM5α has been shown to bind and promote the premature uncoating of incoming retroviral capsids [13-19].Like all TRIM proteins, TRIM5α contains RING, B-box 2 and coiled coil domains [20,21]. The α isoform of TRIM5, which is the only TRIM5 isoform that exhibits antiretroviral activity [7], also has a carboxy-terminal B30.2(SPRY) domain [20,21]. Mutagenic studies have shed light on the contribution of the TRIM5α domains to antiretroviral activity. The RING domain, which exhibits E3 ubiquitin ligase activity, contributes to anti-HIV-1 potency, but is not absolutely required for a modest level of restriction ability [7,13,22