Defensins are a large family of broad-spectrum antimicrobial peptides, identified originally in leukocytes of rabbits and humans. Defensins, cationic/polar peptides (30-35aa; 3-4kD), are distinguished by a conserved tri-disulfides and a largely beta-sheet structure. Defensins, expressed at the cell surface, have been hypothesized to function as a biochemical barrier against microbial infection by inhibiting colonization of the epithelium by wide range of pathogenic microorganisms. In leukocytes, these peptides are stored in cytoplasmic granules and are released into phagolysosomes where they contribute to the killing of engulfed microorganisms. The genes encoding human alpha and beta-defensins are clustered in a contiguous segment of chromosome 8p23. Defensins are classified into two families designated alpha and beta based on distinctive, although similar, tri-disulfide linkages in the peptides. beta-defensins are slightly larger and differ in the position and arrangement of 3 disulfides. In humans, six alpha-defensin (cryptidins), HD 1-6 (HD1-4 are also known as HNP1-4 for Human Neutrophil Peptides), and two beta-defensins, HBD-1 and HBD-2, have been identified. Alpha-defensins are encoded by genes designated DEFA1-6, whereas human beta-defensins are encoded by the DEFB1 and DEFb2 genes. HD1-4 are expressed in neutrophils, whereas HD5 and HD6 are expressed in epithelial cells of the intestinal and reproductive tract. HD1-3/HNP1-3 make up about 30% of the neutrophil's total granule protein. The HNPs are 29-30 amino acids long and are identical in sequence except at the N-terminal amino acid. DEFA1 and DEFA3 differ from each other only by their terminal ala and asp, respectively. DEFA2 is identical to both except that it has 29 instead of 30 amino acids.
Intended for research use only. Not for use in human, therapeutic, or diagnostic applications.