The Candida albicans CDR3 gene codes for an opaque-phase ABC transporter

Abstract

We report the cloning and functional analysis of a third member of the CDR gene family in Candida albicans, named CDR3. This gene codes for an ABC (ATP-binding cassette) transporter of 1,501 amino acids highly homologous to Cdr1p and Cdr2p (56 and 55% amino acid sequence identity, respectively), two transporters involved in fluconazole resistance in C. albicans. The predicted structure of Cdr3p is typical of the PDR/CDR family, with two similar halves, each comprising an N-terminal hydrophilic domain with consensus sequences for ATP binding and a C-terminal hydrophobic domain with six predicted transmembrane segments. Northern analysis showed that CDR3 expression is regulated in a cell-type-specific manner, with low levels of CDR3 mRNA in CAI4 yeast and hyphal cells, high levels in WO-1 opaque cells, and undetectable levels in WO-1 white cells. Disruption of both alleles of CDR3 in CAI4 resulted in no obvious changes in cell morphology, growth rate, or susceptibility to fluconazole. Overexpression of Cdr3p in C. albicans did not result in increased cellular resistance to fluconazole, cycloheximide, and 4-nitroquinoline-N-oxide, which are known substrates for different transporters of the PDR/CDR family. These results indicate that despite a high degree of sequence conservation with C. albicans Cdr1p and Cdr2p, Cdr3p does not appear to be involved in drug resistance, at least to the compounds tested which include the clinically relevant antifungal agent fluconazole. Rather, the high level of Cdr3p expression in WO-1 opaque cells suggests an opaque-phase-associated biological function which remains to be identified.

Structure and mechanism of ATP-dependent phospholipid transporters

“…Interestingly, in contrast to Cdr3p, two other members of the C. albicans Cdr family, Cdr1p and Cdr2p, have been characterized as outward phospholipid transporters [63]. Cdr3p possess 56 and 55% sequence identity to Cdr1p and Cdr2p, respectively, and based on secondary structure predictions, would be expected to fold similarly to these and other Cdr proteins [66]. Likewise, human ABCA4 and its closest homologue, ABCA1, have a similar predicted architecture, but transport phospholipids in opposite directions [65].…”

ABC transporters Cdr1p, Cdr2p and Cdr3p of a human pathogen Candida albicans are general phospholipid translocators

“…CDR3 expression, on the other hand, is linked to phenotypic switching (white-opaque transition) of C. albicans, while no apparent function has been ascribed to CDR4 (Balan et al, 1997;Sanglard et al, 1997;Franz et al, 1998). In this work we have used NBDtagged phospholipid analogues to explore whether Cdrps other than Cdr1p could also mediate transbilayer movement of membrane phospholipids.…”

“…The resistance to azoles in C. albicans, was earlier thought to occur primarily through an alteration or an overexpression of the 14a-lanosterol demethylase (P45014DM) involved in sterol biosynthesis (Lamb et al, 1997;White, 1997). However, the characterization of the first ATP-binding cassette (ABC) protein Cdr1p (Candida drug resistance) by us Krishnamurthy et al, 1998a, b, c;Prasad et al, 1995a;Smriti et al, 1999) and the subsequent identification of other efflux pumps (Balan et al, 1997;Sanglard et al, 1997Sanglard et al, , 1999Calabrese et al, 2000;Franz et al, 1998) and their overexpression in azole-resistant clinical isolates has led to the suggestion that these transporters represent another mechanism involved in multidrug resistance (MDR) scenario of C. albicans (Balan et al, 1997;Sanglard et al, 1997Sanglard et al, , 1999Gupta et al, 1998;Krishnamurthy et al, 1998;Smriti et al, 1999;Calabrese et al, 2000;Franz et al, 1998). In spite of the widespread occurrence of the MDR genes in C. albicans, the molecular mechanisms of their function and the regulation of their expression is yet to be understood (Prasad et al, 1995a.…”

A novel polyamide SL-A92 as a potential fungal resistance blocker: synthesis and bioactivities in Candida albicans

“…Four kinds of CDR genes in C albicans have been cloned [13,[40][41][42] , but only over-expression of CDR1 and CDR2 resulted in azole resistance [43] . Tac1p is the major transcription factor needed for the regulation of CDR1 and CDR2, and is characterized by a highly conserved Zn(II) 2 Cys 6 zinc finger motif formed by six cysteines that coordinate two zinc atoms within the DNAbinding domain [11,44,45] .…”