Figure 5. Influence of C-terminal MPER residues on 2F5 and 2F5_m binding as measured by SPR.

Each bar represents the apparent I100_FS (a) and F100_BS (b) binding affinities in comparison with those of 2F5 for a series of alanine-substituted MPER peptides versus wt MPER. For A667, a D substitution was introduced. The amount of each MPER variant peptide bound to DOPC-DOPG liposome was normalized to that of wt peptide. 30 μl of wt 2F5 at 20 μg ml⁻¹, 2F5_m I100_FS at 35 μg ml⁻¹ and 2F5_m F100_BS at 50 μg ml⁻¹ were injected over peptide–liposome complex at the flow rate of 10 μl min⁻¹. Apparent binding affinities of each antibody for MPER alanine mutants in comparison with the wt peptide were measured by response units taken on the dissociation time point at 3 min following 3 min of association time by BIAcore. (c,d) Binding of 2F5 and mutants to MPER peptides containing or lacking the C-helical MPER region. 20 μg ml⁻¹ of each antibody was injected over peptide-liposome complex except in the case of double mutant L100_AS F100_BS where 100 μg ml⁻¹ was used.