Comparative characterization of candidal cell surface-associated phosphoglycerate mutase (Gpm1) - fungal cell wall...

Some intracellular enzymes are repeatedly detected at the cell surface of fungal pathogens and, due to this noncanonical cellular localization and additional functions played thereon, are classified as multifunctional "moonlighting" proteins. Yet, the extent to which such behaviour is conserved across clinically relevant yeasts and how these proteins interact with the host defence systems remain incompletely recognized. In this work, we investigated the fungal surface accessibility, cell wall adsorption and the interaction with selected host proteins of a glycolytic enzyme - phosphoglycerate mutase (Gpm1) - in four candidal species: Candida albicans, C. parapsilosis, C. tropicalis and Nakaseomyces glabratus (C. glabrata). Surface-accessible Gpm1 was visualized on intact candidal cells by immunofluorescence and detected by immunoblotting in β-1,6-glucanase-released cell wall-associated protein fractions. All species adsorbed exogenous Gpm1 in a concentration-dependent manner, with pseudohyphal/hyphal Candida showing ∼10-fold higher binding than yeast-like cells. Gpm1 showed direct binding to preparations of several major classical adhesins, identifying them as candidate docking partners. Most interactions were with K_D in a ∼10^-7 M order, with weaker binding for C. parapsilosis CPAR2_404800 (∼10^-6 M), stronger binding for N. glabratus Epa6 (∼10^-8 M), and no detectable interaction for Epa3. Anti-Gpm1 antibodies reduced binding of human extracellular matrix proteins and high molecular weight kininogen (HMWK) to fungal cells by 20-25%. Microplate assays confirmed Gpm1 binding to HMWK and low molecular weight kininogen (LMWK), and chemical cross-linking combined with peptide competition mapped a key kininogen-binding region to aa116-136. Taken together, these findings support a conserved capacity of selected classical adhesins to serve as candidate docking partners for exogenous Gpm1 and demonstrate the ability of surface-associated Gpm1 to interact with the host contact system components across pathogenic yeasts.