The Oligomeric State of Human Alpha-Defensin 1 in Solution

Abstract

Defensins are small (18-45 amino acids) proteins present in organisms from plants to humans. They function as host defense peptides, assisting the immune system cells in killing phagocytosed bacteria, and are also active against fungi and viruses. The defensins mode of action is membrane permeabilization - forming fatal, pore-like membrane defects in microbial cells. Since membrane permeabilization models require formation of protein dimers or higher oligomers to open pores in the membrane, the defensins propensity to oligomerize is important to their function and is recently a subject of many research projects. Studying oligomerization of small proteins and peptides presents many challenges. Several methods are suitable to detect oligomeric species, especially after chemical cross-linking, but only the light scattering and analytical ultracentrifugation based measurements allow estimating the equilibrium oligomerization constants without chemical modification of proteins. Still, low scattering light intensity, high diffusion and slow sedimentation rates of peptides make obtaining accurate results difficult. We will present a detailed study of the human alpha-defensin 1 (HNP1) oligomerization. HNP1, prevalent in human neutrophil granulocytes, is not only a potent antimicrobial agent, but was also shown to have cytotoxic activity against many mammalian tumor cells in vitro.