A proteomic analysis of secretory proteins of a pre-vacuolar mutant of Candida albicans.

S. cerevisiae mutants lacking VPS4 missort several vacuolar proteins to the extracellular space, including carboxypeptidase (CPY), vacuolar protease A (PrA), and vacuolar protease B (PrB). In addition, certain soluble secretory proteins, such as invertase and acid phosphatase, are missorted from the pre-vacuolar compartment (PVC) to the general secretory pathway prior to exocytosis. Although little is known about sorting of proteins via the PVC in Candida albicans, we have previously demonstrated that the C. albicans vps4Delta null mutant missorts PrA and CPY extracellularly, but fails to secrete the aspartyl proteases Sap2p and Sap4-6p. To further define the role of C. albicans VPS4 in the trafficking of pre-vacuolar proteins, we have used 2 dimensional gel electrophoresis (2-DE) and mass spectrometry techniques to study soluble proteins in the supernatants of planktonic cultures obtained from the C. albicans vps4Delta mutant compared to control strain DAY185. Results indicated that lack of VPS4 results in a decrease of canonically secreted proteins whilst having a limited effect on non-canonically secreted extracellular proteins. Four canonically secreted proteins (Cht3p, Pra1p, Mp65p and Sun41p) were identified as reduced in the supernatants from the mutant strain. We also indentified two other major consequences of lack of VPS4, likely associated with secretion defects: altered branching and biofilm formation.