Stereoselective interaction of epimeric naproxen-RGD peptides with human serum albumin.

The dependence of the interaction between human serum albumin (HSA) and two epimeric bioconjugates, which contain (S)- or (R)-naproxen (NPX) bound to a cyclopentapeptide with an arginine-glycine-aspartate sequence (cRGD), on the absolute configuration of the naproxen moiety has been studied using several complementary experiments, such as direct physical separation of the unbound compound, fluorescence quenching of the protein, circular dichroism, and laser flash photolysis. The results were compared with those obtained with model compounds, such as (S)- and (R)-NPX, cRGD, and (S)- and (R)-NPX-NHBu amide analogues. Fluorescence quenching of Trp-214 in HSA by the naproxen compounds (NPXs) revealed lower efficiency for (S)-NPX-RGD in quenching the Trp emission as compared to (R)-NPX-cRGD. Laser flash photolysis data together with the association constants gave information about the distribution of each compound in site I and II, as well as about the lifetime of their triplet excited state within each site of HSA. Furthermore, docking modeling agreed with different modes of binding of the epimeric bioconjugates. Thus, although both bioconjugates bound preferentially to site I, only the NPX moiety of (R)-NPX-cRGD was located within the cavity, explaining its efficiency for Trp-214 fluorescence quenching.