Research On The Enhancement Of Antibacterial Activity Of Human Alpha-defensin-3

HNP-3s are peptides of 30 amino acids, containing alkaline amino acid residues and three intra-molecular disulfide bridges. Current publications have shown that HNP-3 has a broad spectrum of antimicrobial activity against gram-negative and gram-positive bacteria, fungi, and enveloped viruses but the antimicrobial activity is blocked in both pro-HNP3 and pre-pro-HNP-3. Here we report our research on the antimicrobial activity of different derivatives of HNP-3 in vitro. cDNA of human pre-pro-HNP-3 was RT-PCR amplified from total RNAs of human white blood cells and cloned into pDEST17 expression vector. The antimicrobial activity of the expressed proteins was examined. As reported previously, (1) pre-pro-HNP-3 and pro-HNP-3 have little antimicrobial activity; (2) HNP-3 can kill both E.coli. and Kleb efficiently. Interestingly, N-His6 sequence fused with pre-pro-HNP-3, pro-HNP-3 and HNP-3 increased the antimicrobial activity dramatically. Further analysis with softwares offered by EXPASY (Expert Protein Analysis System) online indicated that N-His6 sequence can increase PIs of HNP-3 derivatives although the tertiary structures remain unchanged. The enhancement of antimicrobial activity may be attributed to pI increment by N-his6 fusion. Based on these observations, high antimicrobial activity of defensins would be created via increasing electro-positive amino acid residues simply in future.