Defensin is an endogenous antimicrobial peptide. The sequence contains a large amount of cysteine and a certain amount of arginine, of which 6 cysteine randomly form 3 pairs of disulfide bonds. The biological activity of defensins is a spectrum of anti-microbial activity, which plays a vital role in the immune defense mechanism of the organism. Defensin 5 (human) is a peptide consisting of 32 amino acids with 3 pairs of disulfide bonds.