A B-Box 2 Surface Patch Important for TRIM5 Self-Association, Capsid Binding Avidity, and Retrovirus Restriction†

TRIM5 is a tripartite motif (TRIM) protein that consists of RING, B-box 2, coiled-coil, and B30.2(SPRY) domains. The TRIM5rh protein from rhesus monkeys recognizes the human immunodeficiency virus type 1 (HIV-1) capsid as it enters the host cell and blocks virus infection prior to reverse transcription. HIV-1-restricting ability can be eliminated by disruption of the B-box 2 domain. Changes in the TRIM5rh B-box 2 domain have been associated with alterations in TRIM5rh turnover, the formation of cytoplasmic bodies and higher-order oligomerization. We present here the nuclear magnetic resonance structure of the TRIM5 B-box 2 domain and identify an unusual hydrophobic patch (cluster 1) on the domain surface. Alteration of cluster 1 or the flanking arginine 121 resulted in various degrees of inactivation of HIV-1 restriction, in some cases depending on compensatory changes in other nearby charged residues. For this panel of TRIM5rh B-box 2 mutants, inhibition of HIV-1 infection was strongly correlated with higher-order self-association and binding affinity for capsid complexes but not with TRIM5rh half-life or the formation of cytoplasmic bodies. Thus