ABC transporters Cdr1p, Cdr2p and Cdr3p of a human pathogen Candida albicans are general phospholipid translocators.
We have used fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-tagged phospholipid analogues, NBD-PE (phosphatidylethanolamine), NBD-PC (phosphatidylcholine) and NBD-PS (phosphatidylserine), to demonstrate that Cdr1p and its other homologues, Cdr2p and Cdr3p, belonging to the ATP-binding cassette (ABC) superfamily behave as general phospholipid translocators. Interestingly, CDR1 and CDR2, whose overexpression leads to azole resistance in C. albicans, elicit in-to-out transbilayer phospholipid movement, while CDR3, which is not involved in drug resistance, carries out-to-in translocation of phospholipids between the two monolayers of plasma membrane. Cdr1p, Cdr2p and Cdr3p could be further distinguished on the basis of their sensitivities to different inhibitors. For example, the in-to-out activity associated with Cdr1p and Cdr2p is energy-dependent and sensitive to sulphydryl blocking agents such as N-ethylmaleimide (NEM) and cytoskeleton disrupting agent cytochalasin E, while Cdr3p-associated out-to-in activity is energy-dependent but insensitive to NEM and cytochalasin E. We found that certain drugs, such as fluconazole, cycloheximide and miconazole, to which Cdr1p confers resistance could also affect in-to-out transbilayer movement of NBD-PE, while the same drugs had no effect on Cdr3p-mediated out-to-in translocation of NBD-PE. The ineffectiveness of these drugs to affect Cdr3p mediated out-to-in phospholipid translocation further confirms the inherent difference in the directionality of phospholipid translocation between these pumps. Notwithstanding the role of some of the Cdrps in drug resistance, this study clearly demonstrates that these ABC transporters of C. albicans are phospholipid translocators and this function could represent one of the physiological functions of such large family of proteins.
Smriti
Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi-110067 India. rp47@hotmail.com
Krishnamurthy
S
S
Dixit
B L
BL
Gupta
C M
CM
Milewski
S
S
Prasad
R
R
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000935:Antifungal Agents / Q000494:pharmacology; D001692:Biological Transport; D002176:Candida albicans / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D003599:Cytoskeleton / Q000502:physiology; D005656:Fungal Proteins; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014170:Transformation, Genetic
D018528:ATP-Binding Cassette Transporters; D000935:Antifungal Agents; C094693:CDR1 protein, Candida albicans; D002352:Carrier Proteins; C109399:Cdr3 protein, Candida albicans; D005656:Fungal Proteins; D008051:Lipid Bilayers; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids