Increased diversity of intestinal antimicrobial peptides by covalent dimer formation.

Antimicrobial peptides are essential effector molecules of the innate immune system. Here we describe the structure, function and diversity of cryptdin-related sequence (CRS) peptides, a large family of antimicrobial molecules. We identified the peptides as covalent dimers in mouse intestinal tissue in amounts comparable to those of Paneth cell-derived enteric alpha-defensins. CRS peptides caused rapid and potent killing of commensal and pathogenic bacteria. The CRS peptides formed homo- and heterodimers in vivo, thereby expanding the repertoire of antimicrobial peptides and increasing the peptide diversity of Paneth cell secretions. CRS peptides might therefore be important in the maintenance of the microbial homeostasis within the intestinal tract.