Drug susceptibilities of yeast cells are affected when expressing mutant Candida albicans drug resistance protein

In the present study, wild-type and mutant Candida drug resistance protein 1 (Cdr1p) was expressed in Saccharomyces cerevisiae and phenotype alterations were observed in order to understand the importance of Cdr1p in azole resistance. Cdr1p was subjected to site-directed mutagenesis resulting in an alteration (W629L) to transmembrane segment 4 (TMS4). The susceptibilities to azole antifungal drugs of yeast cells as well as passive efflux of Rhodamine 6G were measured. The mutant strain showed greater sensitivity to azole antifungal drugs than the strain with the wild-type plasmid (AD-CDR1) as well as reduced efflux of Rhodamine 6G. Taken together, these phenotypic alterations of yeast cells were caused by the mutation in TMS4 of Cdr1p, which suggests that TMS4 plays a major role in azole antifungal drug efflux and is an azole antifungal drug-binding site.