Transport properties of a C. albicans amino-acid permease whose putative gene was cloned and expressed in S. cerevisiae

Abstract

Using a gene bank of C. albicans, the lysine-permease deficiency in a strain of S. cerevisiae was complemented, and the restriction map of the corresponding C. albicans DNA fragment was constructed. Its expression in S. cerevisiae showed that the permease of C. albicans actively transports arginine (K_T=18 μmol/l, J_max=26 nmol/min per mg dry weight), lysine (K_T=12 μmol/l, J_max=18 nmol/min per mg dry weight), histidine (K_T=37 μmol/l, J_max=9.7 nmol/min per mg dry weight), as well as their toxic analogues canavanine and thialysine, with high affinity. The intracellular concentration of basic amino acids transported into S. cerevisiae by the C. albicans permease reaches more than a thousand-times-higher value compared to the external concentration in the medium. Accumulated amino acids do not leave the cells. The uptake is strongly reduced by the protonophores and inhibitors of plasma membrane H⁺-ATPase.