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Antimicrobial Agents and Chemotherapy, August 2006, p. 2602-2607, Vol. 50, No. 8
0066-4804/06/$08.00+0     doi:10.1128/AAC.00331-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Determination of the Antibacterial and Lipopolysaccharide-Neutralizing Regions of Guinea Pig Neutrophil Cathelicidin Peptide CAP11

Department of Host Defense and Biochemical Research, Juntendo University School of Medicine, Tokyo 113-8421, Japan,¹ Seikagaku Corporation, Tokyo 100-0005, Japan²

Received 17 March 2006/ Returned for modification 11 May 2006/ Accepted 23 May 2006

Previously, we revealed that a cationic antibacterial polypeptide of 11 kDa (CAP11), a member of the cathelicidins isolated from guinea pig neutrophils, exhibits not only potent antibacterial activity but also lipopolysaccharide (LPS)-neutralizing activity. In this study, to determine the biologically active regions of CAP11, we isolated or synthesized the partial peptides of CAP11 and evaluated their antibacterial and LPS-neutralizing activities. Although CAP11 has a unique homodimeric structure with a disulfide bridge, the biological activities of dimeric and monomeric forms of CAP11 were almost the same. Moreover, the G¹-E³³ peptide of CAP11 showed the same activities as CAP11, whereas the C-terminal region (Y³⁴ to I⁴³) possessed no biological activities. In addition, the three 18-mer peptides (G¹-R¹⁸, T⁹-K²⁶, and L¹⁶-E³³) with overlapping sequences were synthesized, and their activities were determined. The three 18-mer peptides retained the antibacterial activities, and G¹-R¹⁸ was the most potent. In contrast, the LPS-neutralizing activities of these peptides were markedly reduced. Together, these observations indicate that the active region with antibacterial activity is localized at G¹ to R¹⁸ of CAP11, whereas longer sequences (such as G¹ to E³³) would be required for the expression of LPS-neutralizing activity. Furthermore, the C-terminal region (Y³⁴ to I⁴³) and a disulfide bridge are not essential for the antibacterial and LPS-neutralizing activities of CAP11.

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