Metal Binding Properties of Fluorescent Analogues of Trichogin GA IV: A Conformational Study by Time-Resolved Spectroscopy and Molecular Mechanics Investigations

The metal ion binding properties of two fluorescent analogues of trichogin GA IV which is a natural undecapeptide showing significant antimicrobial activity, were studied by circular dichroism, time-resolved optical spectroscopy, and molecular mechanics calculations. Binding of Ca(II) and Gd(III) to the peptides investigated was shown to promote a structural transition from highly helical conformations to folded structures characterized by formation of a loop that embedded the metal ion. Time-resolved spectroscopy revealed that peptide dynamics is also remarkably affected by ion binding: peptide-backbone motions slowed down to the microsecond time scale. Finally, molecular mechanics calculations emphasized the role of the central Gly5-Gly6 motif which allowed for the twisting of the peptide segment that gave rise to the formation of the binding cavity.