A MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY APPROACH TO IDENTIFY THE ORIGIN OF THE GLYCAN HETEROGENEITY OF DIPTERICIN, AN O-GLYCOSYLATED ANTIBACTERIAL PEPTIDE FROM INSECTS

In a previous study, electrospray ionization mass spectrometry was use d to analyze the structure of the O-glycopeptide diptericin, an antiba cterial peptide from the fleshfly Phormia terranovae. Several glycofor ms of diptericin differing in the length of their oligosaccharide chai ns were present at the final stage of purification. In order to determ ine the origin of this glycan heterogeneity, we analyzed by matrix-ass isted laser desorption/ionization mass spectrometry (MALDI-MS) the rel ative abundance of the different diptericin glycoforms in fractions ob tained after each purification step, and directly in the hemolymph and in the fat body which produces diptericin. MALDI-MS clearly shows tha t the purification procedure had no effect on the O-linked oligosaccha ride chains of diptericin, suggesting that diptericin is synthesized a s a family of heterogeneous glycopeptides. In addition, in these exper iments, differential mapping by MALDI-MS of the hemolymph and fat body tissue from bacteria-challenged and naive larvae allowed us to detect induced or repressed molecules which may be involved in the immune re sponse of P. terranovae. (C) 1997 Academic Press.