Characterization of luminal paneth cell alpha-defensins in mouse small intestine - Attenuated antimicrobial activities of peptides with truncated amino termini

Paneth cells at the base of small intestinal crypts secrete apical granules that contain antimicrobial peptides including alpha -defensins, termed cry ptdins, Using an antibody specific for mouse cryptdin-1, -2, -3, and -6, im munogold-localization studies demonstrated that cryptdins are constituents of mouse Paneth cell secretory granules. Several cryptdin peptides have bee n purified from rinses of adult mouse small. intestine by gel filtration an d reverse-phase high performance liquid chromatography. Their primary struc tures were determined by peptide sequencing, and their antimicrobial activi ties were compared with those of the corresponding tissue forms. The isolat ed luminal cryptdins included peptides identical to the tissue forms of cry ptdin-2, -4, and -6 as well as variants of cryptdin-1, -4, and -6 that have N termini truncated by one or two residues. In assays of antimicrobial act ivity against Staphylococcus aureus, Escherichia coil, and the defensin-sen sitive Salmonella typhimurium phoP(-) mutant, full-length cryptdins had the same in vitro antibacterial activities whether isolated from tissue or fro m the lumen. In contrast, the N-terminal-truncated (des-Leu), (des-Leu-Arg) -cryptdin-6, and (des-Gly)-cryptdin-4 peptides mere markedly less active. T he microbicidal activities of recombinant cryptdin-4 and (des-Gly)-cryptdin -4 peptides against E. coil, and S. typhimurium showed that the N-terminal Gly residue or the length of the cryptdin-4 N terminus are determinants of microbicidal activity. Innate immunity in the crypt lumen may be modulated by aminopeptidase modification of alpha -defensins after peptide secretion.