The Role of Linker 2 (L2) Region in RhTRIM5α Assembly and HIV-1 Restriction
The cellular restriction factor TRIM5alpha inhibits infection by numerous retroviruses in a species specific manner. TRIM5alpha protein from rhesus macaques (rhTRIM5alpha) and a related protein TRIM-Cyp from Owl monkeys restrict infection by HIV-1 while human TRIM5α (huTRIM5alpha) restricts infection by N-tropic murine leukemia virus (N-MLV) but not HIV-1. Several models have been proposed for retroviral restriction by TRIM5 proteins (TRIM5alpha and TRIMCyp). These models collectively suggest that TRIM5 proteins mediate restriction by recognizing specific determinants in the viral capsid and directly binding the capsid. Following binding, the TRIM5 proteins self-associate into large assemblies around the viral capsid, which leads to either abortive disassembly of the viral capsid via a poorly understood mechanism that is sensitive to proteasome inhibitors and/or activation of innate immune signaling pathways. This study focuses on the initial step in restriction that is assembly of TRIM5alpha around the HIV-1 capsid. TRIM5alpha is known to form assemblies in the cytoplasm of the cell, termed as cytoplasmic bodies. We show that the ability of rhTRIM5alpha to assemble into cytoplasmic bodies is required for HIV-1 restriction and the L2 region has determinants that govern rhTRIM5alpha assembly. Additionally, the L2 variants that have a higher tendency to assemble into cytoplasmic bodies, exhibit increased HIV-1 restriction ability. This suggests that the tendency of rhTRIM5alpha to assemble directly correlates with its HIV-1 restriction ability. We also show that the L2 region of rhTRIM5alpha has a propensity to form alpha-helices that facilitate rhTRIM5alpha assembly, most likely, by mediating protein-protein interactions. This alpha-helical conformation of the L2 region seems to be stabilized in L2 variants that exhibit increased tendency to assemble but not in the variants that fail to assemble. Lastly, the L2 region forms alpha-helices in a concentration dependent manner and possibly acts as a molecular switch in the assembly of rhTRIM5alpha.
alpha-helix, Assembly, HIV-1, Linker 2, Self-Association, TRIM5alpha, Virology
Networked Digital Library of Theses and Dissertations