Adaptation of theleukocidin LukGH for the rabbit host by protein engineering.

Abstract

Host defense againstgreatly depends on bacterial clearance by phagocytic cells. LukGH (or LukAB) is the most potent staphylococcal leukocidin towards human phagocytes, but its role in pathogenesis is obscured by the lack of suitable small animal models because LukGH has limited or no cytotoxicity towards rodent and rabbit compared with human polymorphonuclear cells (PMNs) likely due to an impaired interaction with its cellular receptor, CD11b. We aimed at adapting LukGH for the rabbit host by improving binding to the rabbit homolog of CD11b, specifically its I-domain (CD11b-I). Targeted amino acid substitutions were introduced into the LukH polypeptide to map its receptor interaction site(s). We found that the binding affinity of LukGH variants to the human and rabbit CD11b-I correlated well with their PMN cytotoxicity. Importantly, we identified LukGH variants with significantly improved cytotoxicity towards rabbit PMNs, when expressed recombinantly (10-15-fold) or by engineeredstrains. These findings support the development of small animal models ofinfection with the potential for demonstrating the importance of LukGH in pathogenesis.