NMR study on a SRYD-containing fibronectin-like sequence (250–257) of Leishmania gp63: contribution of residual water in the dimethyl sulfoxide solution structure

The conformational characteristics of the I250ASRYDQL257 synthetic octapeptide, which incorporates the SRYD adhesion site (252–255) of Leishmania gp63, have been investigated at pH 2 and 5, by means of 1 D and 2D 1H NMR spectroscopy (temperature coefficient values, chemical shifts, vicinal coupling constants and NOE effects). It was found that elimination of residual water from the dimethyl sulfoxide (DMSO) solution at pH 2 provides exchange peaks in the ROESY and HOHAHA spectra similar to those obtained for the DMSO peptide solution at pH 5. This common structure is stabilized (i) by the formation of a type I β-turn involving the QNH→RCO interaction and (ii) by a possible interaction between the guanidinium and the D-β-carboxylate groups. After treatment with molecular sieves, the remaining residual water is redistributed between the peptide functional groups and participates in the rigidification of the new conformational state.