Functional analysis of Candida albicans Cdr1 through homologous and heterologous expression studies

Candida albicans Cdr1 is a plasma membrane ATP-binding cassette transporter encoded by CDR1 that was first cloned 30 years ago in Saccharomyces cerevisiae. Increased expression of Cdr1 in C. albicans clinical isolates results in resistance to azole antifungals due to drug efflux from the cells. Knowledge of Cdr1 structure and function could enable the design of Cdr1 inhibitors that overcome efflux-mediated drug resistance. This article reviews the use of expression systems to study Cdr1. Since the discovery of CDR1 in 1995, 123 studies have investigated Cdr1 using either heterologous or homologous expression systems. The majority of studies have employed integrative transformation and expression in S. cerevisiae. We describe a suite of plasmids with a range of useful protein tags for integrative transformation that enable the creation of tandem-gene arrays stably integrated into the S. cerevisiae genome, and a model for Cdr1 transport function. While expression in S. cerevisiae generates a strong phenotype and high yields of Cdr1, it is a nonnative environment and may result in altered structure and function. Membrane lipid composition and architecture affects membrane protein function and a focus on homologous expression in C. albicans may permit a more accurate understanding of Cdr1 structure and function.