Structure and variability of TRIM22 and TRIM5α protein domains. TRIM22 contains an amino-terminal RING domain, one B-box domain (B-box 2), a coiled-coil region, and a carboxyl-terminal B30.2 domain (SP1 = Spacer 1 and SP2 = Spacer 2). Two cysteine residues (Cys15 and Cys18) in the RING domain are required for the E3 ligase activity of TRIM22, and a number of positively selected amino acids are found in the coiled-coil and B30.2 domains. The location and spacing of positively selected amino acids in TRIM22 are similar to those found in TRIM5α, which may reflect species-specific pathogenic pressures. The approximate location of positively selected amino acids in TRIM22 and TRIM5α is denoted with a star, and the location of the β2-β3 surface loop of TRIM22 is also indicated (arrows). Single nucleotide polymorphisms (SNPs) in the coding regions of TRIM22 and TRIM5α are shown as vertical bars, along with the type of mutation that each SNP can generate (green: nonsynonymous mutations; yellow: missense mutations; pink: frameshift mutations; red: nonsense mutations).
