Analysis of Candida albicans plasma membrane proteome

Abstract

The opportunistic human fungal pathogen Candida albicans causes a wide variety of infections including deep systemic syndromes. The C. albicans plasma membrane is an important interface in the host-pathogen relationship. The plasma membrane proteins mediate a variety of functions, including sensing and signalling to the external environment, in which the glycosylphosphatidylinositol (GPI)-anchored membrane proteins play a crucial role. A subproteomic approach to obtain a global picture of the protein composition of the C. albicans plasma membrane was developed, and different strategies were tested in order to extract the largest number of yeast plasma membrane proteins and GPI-anchored membrane proteins. These methods involved: (i) protoplast generation, (ii) mechanical disruption, (iii) ultracentrifugation in sucrose gradients, and (iv) Na(2)CO(3) treatments. To isolate GPI-anchored proteins two additional steps were performed: two-phase separation and phosphatidylinositol-phospholipase C treatment. After LC-MS/MS analysis using both a MALDI-TOF/TOF and a linear ion trap quadrupole, a total of 214 membrane proteins were identified, including 41 already described as plasma membrane proteins, 20 plasma membrane associated proteins, and 22 proteins with unknown membrane localisation. Bioinformatic analysis revealed that this set of C. albicans membrane proteins is highly enriched in proteins involved in biopolymer biosynthesis or transport processes. Furthermore, after phosphatidylinositol-phospholipase C treatment, 12 GPI-anchored membrane proteins were released and identified; most of them are associated with cell wall beta-glucan synthesis and maintenance or are virulence factors, such as phospholipases or aspartyl proteinases.