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 used to analyze the structure of the O-glycopeptide diptericin, an antibacterial peptide from the fleshfly Phormia terranovae. Several glycoforms of diptericin differing in the length of their oligosaccharide chains were present at the final stage of purification. In order to determine the origin of this glycan heterogeneity, we analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) the relative abundance of the different diptericin glycoforms in fractions obtained after each purification step, and directly in the hemolymph and in the fat body which produces diptericin. MALDI-MS clearly shows that the purification procedure had no effect on the O-linked oligosaccharide chains of diptericin, suggesting that diptericin is synthesized as a family of heterogeneous glycopeptides. In addition, in these experiments, 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 response of P. terranovae.