The lipopeptide antimycotic, cilofungin modulates the incorporation of glucan-associated proteins into the cell wall of Candida albicans

Abstract

The effect of the beta 1-3 glucan synthase inhibitor, cilofungin, on the incorporation of 35S-methionine-labelled glucan associated proteins (GAP) in the cell wall of Candida albicans was investigated in a susceptible strain C. albicans 3153 and resistant strain C. albicans CA-2. Cilofungin exerted a marked effect on the GAP composition of the cell wall at 0.25 mg/L, a concentration which reduced beta 1-3 glucan synthesis by approximately 50% and also inhibited the growth of the susceptible strain C. albicans 3153. A 46 kDa protein was present in large amounts in C. albicans 3153 but not in strain CA-2. This protein was probably not mannosylated and its incorporation was greatly reduced by cilofungin. In addition, a well defined 34 kDa protein was identified together with a distinct band of high molecular mass polydisperse material of between 65 and 96 kDa and another of > 200 kDa. These proteins were strongly reactive to concanavalin A indicating that they were mannosylated, and treatment with cilofungin caused an increase in their production which was also confirmed by immunoblotting with rabbit anti-Candida serum. In contrast, exposure of the drug-resistant strain CA-2 to cilofungin did not result in changes in the composition of the GAP constituents. Only the mannosylated proteins of 34 kDa and the high molecular mass polydisperse material 65-96 kDa were present in the cell wall. The pulse-chase labelling experiments showed that the 46 kDa protein was the first of the GAPs to be incorporated into the cell wall, and that this was suppressed in the presence of cilofungin whereas there was a concomitant increase in the incorporation of the 34 kDa and the high-molecular weight polydisperse material. Thus, cilofungin causes a profound imbalance in GAP incorporation into the growing cell wall which is possibly related to changes in the amount and type of glucan being synthesized at sub-inhibitory concentrations of the antimycotic.