The antimicrobial activity of CCL28 is dependent on C-terminal positively-charged amino acids

Several chemokines have been shown to act as antimicrobial proteins, suggesting a direct contribution to innate immune protection. Based on the study of defensins and other antimicrobial peptides, it has been proposed that cationic amino acids in these proteins play a key role in their antimicrobial activity. The primary structure requirements necessary for the antimicrobial activity of chemokines, however, have not yet been elucidated. Using mouse CCL28, we have identified a C-terminal region of highly-charged amino acids (RKDRK) that is essential to the antimicrobial activity of the murine chemokine. Additionally, other positively-charged amino acids in the C-terminus of the protein contribute to the observed antimicrobial effect. Charge reversal and deletion mutations support our hypothesis that C-terminal positively-charged amino acids are essential for the antimicrobial activity of CCL28. Results also demonstrate that although the C-terminal region of the chemokine is essential, it is not sufficient for full antimicrobial activity of CCL28.