A New Endogenous Overexpression System of Multidrug Transporters of Candida albicans Suitable for Structural and Functional Studies

Fungal pathogens have a robust array of multidrug transporters which aid in active expulsion of drugs and xenobiotics to help them evade toxic effects of drugs. Thus, these transporters impose a major impediment to effective chemotherapy. Although the Saccharomyces cerevisiae strain AD1-8u(-) has catered well to the need of an overexpression system to study drug transport by multidrug transporters of Candida albicans, artifacts associated with a heterologous system could not be excluded. To avoid the issue, we exploited a azole-resistant clinical isolate of C. albicans to develop a new system devoid of three major multidrug transporters (Cdr1p, Cdr2p, and Mdr1p) for the overexpression of multidrug transporters under native hyperactive CDR1 promoter due to gain of function (GOF) mutation in TAC1. The study deals with overexpression and functional characterization of representatives of two major classes of multidrug transporters, Cdr1p and Mdr1p, to prove the functionality of this newly developed endogenous expression system. Expression of native Cdr1 and Mdr1 protein in C. albicans cells was confirmed by confocal microscopy and immunodetection and resulted in increased resistance to the putative substrates as compared to control. The system was further validated by overexpressing a few key mutant variants of Cdr1p and Mdr1p. Together, our data confirms the utility of new endogenous overexpression system which is devoid of artifactual factors as most suited for functional characterization of multidrug transporter proteins of C. albicans.