Figure 3. Trimeric arrangement of MA molecules.
(A) Top down and (B) transverse views of the MA trimer structure as solved by Hill et al. [31]. Residues that can be mutated to block Env incorporation are shown in blue (L12, E16, L30, V34 and E98). Residues that can be mutated to restore Env incorporation are shown in green (Q62, S66); these residues are in a position to form interactions across the trimer interface to effect restoration of Env incorporation. Residue T69 (red) can be mutated to prevent Env incorporation but is not compensated by modifications of the trimer interface. Mutation of T69 has been suggested to block MA trimerization [24]. (C) and (D) show a MA monomer mapped onto non-trimeric and trimeric lattices, respectively, as described by Alfadhli et al., [40,42]. Positions of mutations that block Env incorporation are shown in blue. Trimerization enlarges the central aperture of the MA lattice (from < 3 nm to > 4 nm), which is lined by the inhibitory mutations. Together these data suggest a role for the central aperture in accommodating the gp41 CT. The model of MA monomer and trimer were generated in Pymol (www.pymol.org) based on the Protein Data Bank coordinates 1HIW [39].