Enzymes of the lysine biosynthetic pathway as targets for antifungals

Systemic infections caused by human pathogenic fungi in immunocompromized patients continue to be one of the important clinical problems. Limited availability of safe and efficacious antifungal chemotherapeutics and emerging resistance to existing drugs stimulates search for novel molecular targets for antifungals. The α-aminoadipate pathway (AAP) of L-lysine biosynthesis is unique in fungi and thus has been so far considered one of the potential targets for the rational design of antifungal drugs [1]. In the present communication we report results of our studies on characterization of four enzymes catalyzing initial steps of AAP from the opportunistic fungal pathogen Candida albicans: homocitrate synthase (HCS), homoaconitase (HA), homoisocitrate dehydrogenase (HICD) and α-aminoadipate aminotransferase (AadAT). The appropriate genes were cloned from the C. albicans genomic DNA, expressed in E. coli, their products were isolated as oligoHis-tagged proteins and characterized in terms of steady-state kinetic parameters, substrate specificity and cofactor requirements. Differences in the enzymatic properties of two isoforms of HCS encoded by the LYS21 and LYS22 genes were noted.Several potential inhibitors of the AAP enzymes were designed, synthesized and tested for their enzyme inhibitory potential. Finally, virulence of the constructed lys21Δ/lys22Δ mutant of C. albicans in the disseminated murine candidiasis model was compared to that of the wild-type strain. Conclusions questioning a possibility of exploitation of AAP enzymes as targets in chemotherapy of systemic fungal infections have been presented. [1] Xu, H., et al., Cell Biochem Biophys, 46, 43-64 (2006)