Directed Mutational Strategies Reveal Drug Binding and Transport by the MDR Transporters of Candida albicans

Abstract

Multidrug resistance (MDR) transporters belonging to either the ATP-Binding Cassette (ABC) or Major Facilitator Superfamily (MFS) groups are major determinants of clinical drug resistance in fungi. The overproduction of these proteins enables the extrusion of incoming drugs at rates that prevent lethal effects. The promiscuity of these proteins is intriguing because they export a wide range of structurally unrelated molecules. Research in the last two decades has used multiple approaches to dissect the molecular basis of the polyspecificity of multidrug transporters. With large numbers of drug transporters potentially involved in clinical drug resistance in pathogenic yeasts, this review focuses on the drug transporters of the important pathogen Candida albicans. This organism harbors many such proteins, several of which have been shown to actively export antifungal drugs. Of these, the ABC protein CaCdr1 and the MFS protein CaMdr1 are the two most prominent and have thus been subjected to intense site-directed mutagenesis and suppressor genetics-based analysis. Numerous results point to a common theme underlying the strategy of promiscuity adopted by both CaCdr1 and CaMdr1. This review summarizes the body of research that has provided insight into how multidrug transporters function and deliver their remarkable polyspecificity.

Spontaneous suppressors against debilitating transmembrane mutants of CaMdr1 disclose novel interdomain communication via Signature motifs of the Major Facilitator Superfamily

“…In addition, residues conferring polyspecificity (orange) are still localized at the periphery of those involved in substrate binding (green), which strengthens our previous finding that such pattern is a molecular feature of MDR pumps polyspecificity (Redhu et al . 2018; Banerjee et al . 2021).…”

K143R Amino Acid Substitution in 14-α-Demethylase (Erg11p) Changes Plasma Membrane and Cell Wall Structure of Candida albicans

“…An example of the resistance mechanism is the presence of point mutations in ERG11 (especially near the active site of the enzyme), resulting in a decreased binding affinity of the azoles to Erg11p [7,10]. Another azole resistance strategy is an altered sterol composition in the PM of C. albicans and increased expression of ERG11 due to the upregulation of its transcription factor UPC2, and the overexpression of the genes encoding multidrug resistance transporters (e.g., CDR1, CDR2) [10,11].…”

Genomic landscape of the DHA1 family in the newly emerged pathogen Candida auris and mapping substrate repertoire of the prominent member CauMdr1

“…However, one study showed that deletion of the gene did not result in a major alteration in the MICs. Nonetheless, it is worth mentioning that there is a significant overlap between the substrate repertoire of DHA1 transporters and ABC transporters, and function of one protein might not be apparent in the presence of a large number of other such proteins (Banerjee et al, 2021). Further research is still in infancy and more studies with a larger panel of isolates are required to understand contributions of these important class of proteins to antifungal resistance.…”

“…While a clinical correlation of ABC transporter encoding gene and azole resistance has been experimentally deduced, the same is yet unknown for the other major class of drug transporters in Candida species, the Major Facilitator superfamily (MFS) (Prasad et al, 2019(Prasad et al, , 2017. Within the MFS of fungi, the drug/H + antiporter 1 family (DHA1) proteins have shown capability to recognize and export a wide variety of xenobiotic compounds, including drugs like azoles (Banerjee et al, 2021;Prasad et al, 2017). The major clinically relevant DHA1 transporter in Candida species is Mdr1 and gene encoding for its homolog also exists in C. auris, which shows increased transcript levels in resistant isolates (Bravo Ruiz and Lorenz, 2021;Jenull et al, 2021;Rybak et al, 2019).…”