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. 2013 Jun 18;8(6):e65950. doi: 10.1371/journal.pone.0065950

Figure 5. A model for the transition from R5 to X4 C-HIV phenotype in subject 1109.

Figure 5

Close up views of the V3 loop structure of the R5 1109-E-10 gp120 (left), possible R5X4 intermediates (center, top and bottom) and the X4 1109-F-30 gp120 (right). Amino acid residues that contribute to the acquisition of CXCR4-usage in patient 1109, as determined by the Env mutagenesis studies, are represented as stick models and their molecular surface is colored according to polarity (white, non-polar; blue, positively charged). In this model, Envs that acquire either Arg318 (center, top) or the Ile314-Gly315 insertion (center, bottom) in the context of additional gp120 “scaffold” mutations are possible “transitional” R5X4 intermediates, with X4-phenotype conferred by the acquisition of both changes (right).