Do proline-rich proteins modulate a transglutaminase catalyzed mechanism of candidal adhesion?

Previously, we reported that a membrane-bound epithelial enzyme, transglutaminase (TGase), catalyzes the covalent cross-linking of acidic proline-rich proteins (APRPs) to surface proteins of buccal epithelial cells (BECs). The purpose of this study was twofold: (1) to provide evidence that TGase stabilizes C. albicans adhesion by covalently cross-linking C. albicans and BEC surface proteins and (2) to implicate PRPs in the modulation of this adhesive mechanism. The reactivity of candidal cell wall proteins with TGase was assessed in two separate experiments. Initially, following incubation with native BECs, the cross-linking of iodinated candidal cell wall proteins into high-molecular-weight complexes, as shown by SDS-PAGE/autoradiography, was inhibited by the TGase inhibitor iodoacetamide. Additionally, [14C]putrescine in the presence of purified TGase, but not [14C]putrescine alone, was shown by SDS-PAGE/fluorography to be cross-linked into surface proteins of both morphogenetic forms (blastospore > hyphal forms) of C. albicans. In adherence assays, a component of both blastospore and hyphal form Candida/BEC adherence was shown to be resistant to detachment by heating adherent cells in 1% SDS at 100 degrees C. However, pretreatment of BECs with iodoacetamide decreased SDS resistant adherence of both forms of C. albicans by approximately 75%. When incubated with [125I]APRPs and purified TGase, both morphogenetic forms of C. albicans bound dramatically more APRP than controls without TGase. [125I]APRP binding in experimental, but not control, samples was resistant to repeated extraction (48 h) with 4% SDS/10% beta-mercaptoethanol at 65 degrees C, suggesting that [125I]APRPs were cross-linked to the Candida surface.(ABSTRACT TRUNCATED AT 250 WORDS)