Antimicrobial peptides - defensins

Numerous organisms produce antimicrobial peptides (AMP) as part of their innate immunity and host defense. Antimicrobial peptides are implicated in antibacterial as well as antifungal activity in phagocytes, inflammatory fluids and intestinal secretions. Among them, the most abundant and the best characterized are defensins. Most of them have been recently sequenced and their structures have been solved. Defensins are small (about 5 kDa), mainly basic, cystein - rich peptides. The global fold comprises an antiparallel p sheet and an a helix, which is stabilized by disulfide bridges. The mammalian defensins can be subdivided into three main classes according to their structural differences: alpha, beta and, recently described, theta defensins. Several models have been recently proposed to explain the mechanism of bacterial membrane perturbation by defensins, leading to pore formation. This review describes recent findings in defensin biology focusing mainly on mammalian defensins.