NMR-STUDY ON A SRYD-CONTAINING FIBRONECTIN-LIKE SEQUENCE-(250-257) OFLEISHMANIA-GP63 - CONTRIBUTION OF RESIDUAL WATER IN THE DIMETHYL-SULFOXIDE SOLUTION STRUCTURE

The conformational characteristics of the I(250)ASRYDQL(257) synthetic octapeptide, which incorporates the SRYD adhesion site (252-255) of L eishmania gp63, have been investigated at pH 2 and 5, by means of 1D a nd 2D H-1 NMR spectroscopy (temperature coefficient values, chemical s hifts, vicinal coupling constants and NOE effects). It was found that elimination of residual water from the dimethyl sulfoxide (DMSO) solut ion at pH 2 provides exchange peaks in the ROESY and HOHAHA spectra si milar to those obtained for the DMSO peptide solution at pH 5. This co mmon structure is stabilized (i) by the formation of a type I beta-tur n involving the QNH --> RCO interaction and (ii) by a possible interac tion between the guanidinium and the D-beta-carboxylate groups. After treatment with molecular sieves, the remaining residual water is redis tributed between the peptide functional groups and participates in the rigidification of the new conformational state.