Purification, primary structures, and antibacterial activities of ␤-defensins, a new family of antimicrobial peptides from bovine neutrophils.

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The role of the carboxyl-terminal portion of the alpha chains of fibrin (alpha C domains) in clot formation was investigated by transmission and scanning electron microscopy and turbidity studies of clots made from preparations of molecules missing one or both of these domains. Highly purified and entirely clottable preparations of bovine fragment X monomer, one containing primarily molecules missing a single alpha C domain (fragment X1) and the other consisting of molecules missing both alpha C domains (fragment X2), were used for these experiments. These preparations were characterized by various methods, including the complete determination of the amino- and carboxyl-termini of all peptides and fragments. These preparations formed clots on dilution to neutral pH. In all cases, clots observed by either scanning or transmission electron microscopy were made up of a branched network of fibers, similar to those formed by thrombin treatment of intact fibrinogen, suggesting that the alpha C domains are not necessary for protofibril and fiber formation or branching. However, both the fiber and clot structure varied with the different fractions, indicating that the alpha C domains do participate in polymerization. The rate of assembly, as indicated by the lag period and maximum rate of turbidity increase, as well as the final turbidity, was decreased with removal of the alpha C domains, suggesting that they accelerate polymerization. preparations of isolated alpha C fragment added to fibrin monomer have striking effects on the turbidity curves, showing a decrease in the rate of polymerization in a dose-dependent manner but not complete inhibition. Electron microscopy of fibrin monomer desA molecules at neutral pH showed that most of the alpha C domains, like those in fibrinogen, remain associated with the central region. Thus, it appears that normally with thrombin cleavage of fibrinogen the effects of the interactions of alpha C domains observed here will be most significant for lateral aggregation.

Abstract. Five intestinal defensins, termed cryptdins 1-5, have been purified from mouse smaU bowel, sequenced, and localized to the epithelium by immunohistochemistry. Although identified as members of the defensin peptide family by peptide sequencing, enteric defensins are novel in that four cryptdins have amino termini which are three to six residues longer than those of leukocyte-derived defensins. A fifth cryptdin is the first defensin to diverge from the previously invariant spacing of cysteines in the peptide structure. The most abundant enteric defensin, cryptdin-1, had antimicrobial activity against an attenuated phoP mutant of Salmonella typhimurium but was not active against the virulent wild-type parent. Immunohistochemical localization demonstrated that cryptdin-1, and probably cryptdins 2 and 3, occur exclusively in Paneth cells, where the peptides appear to be associated with cytoplasmic granules. Biochemical and immunologic analysis of the luminal contents of the small intestine suggest that cryptdin peptides are secreted into the lumen, similar to Paneth cell secretion of lysozyme. The presence of several enteric defensins in the intestinal epithelium, evidence of their presence in the lumen, and the antibacterial activity of cryptdin-1 suggest that these peptides contribute to the antimicrobial barrier function of the small bowel mucosa.

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