CD AND NMR STRUCTURAL CHARACTERIZATION OF CERATOTOXINS, NATURAL PEPTIDES WITH ANTIMICROBIAL ACTIVITY

Antibacterial properties of the secretion from the female reproductive accessory glands of medfly Ceratitis capitata are mostly ascribed to the presence of two peptides, ceratotoxin A and B, which exhibit a str ong activity against gram-positive and gram-negative bacterial strains , and show sequence and function homology with cecropins, melittin, an d magainins. CD experiments performed in different solvents indicate t he presence of a significant content of helical structures in organic solvent. Two-dimensional nmr results for ceratotoxin A in methanol sho w a helical behavior for the 8-25 region of the peptide. A Ramachandra n classification of each residue for the structures obtained from dist ance geometry calculations lead to the definition of four structural f amilies in which the central segment 10-19 is always helical and diffe rences refer to residues 8-9 and 19-23, A sequence analysis of the two ceratotoxins and a systematic search on the protein data bank reveale d the occurrence of a KX-hydrophobic-hydrophobic-P motif that seems to be important for helix stabilization. (C) 1996 John Wiley & Sons, Inc .