The Candida albicans CTR1 gene encodes a functional copper transporter

Abstract

Copper and iron uptake in Saccharomyces cerevisiae are linked through a high-affinity ferric/cupric-reductive uptake system. Evidence suggests that a similar system operates in Candida albicans. The authors have identified a C. albicans gene that is able to rescue a S. cerevisiae ctr1/ctr3-null mutant defective in high-affinity copper uptake. The 756 bp ORF, designated CaCTR1, encodes a 251 amino acid protein with a molecular mass of 27·8 kDa. Comparisons between the deduced amino acid sequence of the C. albicans Ctr1p and S. cerevisiae Ctr1p indicated that they share 39·6 % similarity and 33·0 % identity over their entire length. Within the predicted protein product of CaCTR1 there are putative transmembrane regions and sequences that resemble copper-binding motifs. The promoter region of CaCTR1 contains four sequences with significant identity to S. cerevisiae copper response elements. CaCTR1 is transcriptionally regulated in S. cerevisiae in response to copper availability by the copper-sensing transactivator Mac1p. Transcription of CaCTR1 in C. albicans is also regulated in a copper-responsive manner. This raises the possibility that CaCTR1 may be regulated in C. albicans by a Mac1p-like transactivator. A C. albicans ctr1-null mutant displays phenotypes consistent with the lack of copper uptake including growth defects in low-copper and low-iron conditions, a respiratory deficiency and sensitivity to oxidative stress. Furthermore, changes in morphology were observed in the C. albicans ctr1-null mutant. It is proposed that CaCTR1 facilitates transport of copper into the cell.

The CaCTR1 gene is required for high-affinity iron uptake and is transcriptionally controlled by a copper-sensing transactivator encoded by CaMAC1

“…A Cactr1-null mutant displayed phenotypes that were similar to those of a S. cerevisiae mutant defective in high-affinity copper uptake. Furthermore, this mutant grew predominantly in the filamentous form and also displayed aberrant morphology in response to copper-depleted growth conditions (Marvin et al, 2003). We demonstrate here that invasive growth by C. albicans is induced by low-copper conditions and that this is augmented in a Cactr1-null strain.…”

“…We have also shown that a double-disrupted Cactr1-null mutant grows prevalently in the filamentous form in liquid MD-BCS medium, with many cells displaying aberrant morphology (Marvin et al, 2003). These findings led us to hypothesize that copper starvation also induces invasive growth in C. albicans.…”

“…Interestingly, the phenotypes displayed by a Cactr1-null mutant did not coincide with a drop in cell membrane p-phenylenediamine (PPD) oxidase activity. CaCTR1 is transcriptionally controlled by the copper-sensing transactivator ScMac1p when it is heterologously expressed in S. cerevisiae (Marvin et al, 2003). Here, we show that a similar transactivator exists in C. albicans and is required for expression of CaCTR1 in response to low-copper conditions.…”

“…We have also shown that when heterologously expressed in S. cerevisiae, CaCTR1 is transcriptionally controlled in a similar manner to C. albicans and this control is facilitated by the copper-sensing transactivator ScMac1p (Marvin et al, 2003).…”

“…The bottom layer consisted of MD medium without added copper and the top layer consisted of MD-BCS medium without added copper. A concentration of 1?5 mM of the copper chelator BCS was used in the top layer as we have previously shown this concentration to be close to the threshold of growth or non-growth of a Cactr1-null mutant on this medium (Marvin et al, 2003).…”