ABSTRACT
The rapidly growing family of transporters particularly belonging to ABC superfamily (traffic ATPases) comprises an extremely diverse class of membrane transport proteins that couple ATP hydrolysis to the translocation of solutes across the membrane. The diversity of these proteins is also reflected in their ever-emerging additional roles in absorption, excretion, signal transduction, bacterial pathogenesis, and most importantly, drug and antibiotic resistance [118, 119J. Understandably, considerable attention is being given to the physiological relevance of ABC transporters. The most intriguing aspect of these transporters relates to their wider specificity, where a single transporter can recognize a variety of unrelated xenobiotics. As discussed above, there are already several energy-dependent transporters, which have been identified in Candida and other pathogenic fungi and some of them have been shown to be involved in drug transport [31,32,88,89]. The S. cerevisiae genome completion revealed that it has 29 ABC transporters and an almost equal number of MFS transporters [112,120]. Therefore, it is very likely that Candida could also harbor a lot more transporters than what have been discovered so far. Considering the diversity and large size of such proteins [121,122] it is believed that such a large family of transporters may not exclusively export drugs in fungi. Understanding the molecular mechanism of transmembrane transport in general and of antifungal resistance in particular is important for the improved management of C. albicans infection. Recent evidence suggests that ABC transporters of fungi, C. albicans in particular, are multifunctional proteins with important physiological functions. The following sections describe the so far identified physiological roles for these proteins.
