Paneth cell trypsin is the processing enzyme for human defensin-5

Abstract

The antimicrobial peptide human alpha-defensin 5 (HD5) is expressed in Paneth cells, secretory epithelial cells in the small intestine. Unlike other characterized defensins, HD5 is stored in secretory vesicles as a propeptide. The storage quantities of HD5 are approximately 90 450 microg per cm2 of mucosal surface area, which is sufficient to generate microbicidal concentrations in the intestinal lumen. HD5 peptides isolated from the intestinal lumen are proteolytically processed forms--HD5(56-94) and HD5(63-94)--that are cleaved at the Arg55-Ala56 and Arg62-Thr63 sites, respectively. We show here that a specific pattern of trypsin isozymes is expressed in Paneth cells, that trypsin colocalizes with HD5 and that this protease can efficiently cleave HD5 propeptide to forms identical to those isolated in vivo. By acting as a prodefensin convertase in human Paneth cells, trypsin is involved in the regulation of innate immunity in the small intestine.

Human α-defensins block papillomavirus infection

“…In Paneth cells, this processing is accomplished by tryptic digestion during or just after secretion into the intestinal lumen (55). A recent report has shown that, in the male urethra, HD-5 processing may depend on proteases secreted by neutrophils (50).…”

Reduced Paneth cell α-defensins in ileal Crohn's disease

“…Protein extracts from ileal mucosa were isolated from randomly selected controls, CD NOD2͞CARD15 wild-type and CD NOD2͞CARD15 SNP13 patients, as described (35). Protein expression of HD5, ␣-1-trypsin inhibitor, lysozyme, and sPLA 2 in the patient samples was quantified by immunoblotting, as described (36).…”

“…Cationic proteins from ileal mucosal biopsies were isolated by using a weak cation exchange matrix, as described (35). Assays were normalized to protein concentration, as determined by Bradford assay.…”

Functional Determinants of Human Enteric α-Defensin HD5

“…In humans, six members of the ␣-defensin family have been described: human neutrophil peptides 1-4 (HNP1 to -4) present in the neutrophil granules (19 -22) and human defensin 5 and 6 (HD5 and -6) secreted by the Paneth cells of the intestinal crypts (23,24). Each of the six ␣-defensins is expressed with a pro-domain, which functions in sorting to the correct compartment, the inhibition of activity while the pro-peptide is still attached, and the facilitation of the correct folding of the mature defensin (25)(26)(27)(28)(29)(30)(31).…”

“…Collectively, these studies have provided important insights into the structural and functional roles of disulfide bonding (51,52), cationicity (53,54), and conserved elements, such as the Arg-Glu salt bridge (55)(56)(57)(58) and invariant Gly residue (59,60) in the action of ␣-defensins. Recently, a comprehensive Ala scanning mutagenesis of HNP1 has discovered that a hydrophobic residue near the C terminus, Trp 26 , governs the ability of this ␣-defensin to kill Staphylococcus aureus, inhibit anthrax lethal factor, and bind HIV-1 envelope glycoprotein gp120 (61); methylation of a peptide bond at the putative dimer interface of HNP1 debilitates its dimerization and is functionally detrimental (62). Despite structural conservation, mammalian ␣-defensins share rather limited sequence identity.…”