Background:  HIV-1 can enter the cells of all Old World primates, yet the epidemic is confined to humans and apes. Recently, a genetic screen identified the cytoplasmic body component TRIM5a as a major post-entry restriction factor in Old World monkey cells. TRIM5a is a member of a large, but poorly characterized family of proteins defined by a tripartite motif consisting of RING, B-box 2, and coiled-coil domains. TRIM5a is the largest of the TRIM5 isoforms and contains a C-terminal B30.2(SPRY) domain. Rhesus monkey TRIM5a more potently blocks HIV-1 infection than human TRIM5a. Analysis of species-specific variation in TRIM5a has identified 3 variable regions (v1, v2, and v3) within the B30.2(SPRY) domain. The TRIM5a proteins of Old World primates exhibit expansion, duplication, and residue variation specifically in the v1 region.

Methods:  We constructed a panel of rhesus and human chimeric TRIM5a proteins. Stable cell lines expressing these chimeric proteins were tested for susceptibility to infection with HIV-1-GFP viruses.

Results:  By analyzing the chimeric TRIM5a proteins we show that the major determinant of anti-HIV-1 potency is the B30.2(SPRY) domain. Replacement of 3 amino acids in the N-terminus of the human TRIM5a B30.2 v1 region resulted in a molecule that restricted HIV-1 nearly as efficiently as wild type rhesus TRIM5a. Surprisingly, a single amino acid change in this region of human TRIM5a allowed potent restriction of SIV_mac, a phenotype not observed for either wild type human or rhesus TRIM5a.

Conclusions:  Chimeric TRIM5a proteins that are more than 98% identical to the human protein can potently block HIV-1. These proteins may have therapeutic utility, and also provide important mechanistic insights into TRIM5a antiviral activity.

Keywords: HIV-1 restriction; TRIM5alpha; Old World Monkeys