Evidence for the presence of collagenous domains in Candida albicans cell surface proteins

Abstract

Rabbit polyclonal antibodies (PAbs) directed towards the amino-terminal cysteine-rich 7S domain (PAb anti-7S), the major internal collagenous domain (PAb anti-type IV), and the C-terminal noncollagenous region (PAb anti-NC1) of the type IV collagen molecule were probed by indirect immunofluorescence against Candida albicans blastoconidia and germinated blastoconidia. Most nongerminating cells and mother blastoconidia from which germ tubes originated showed strong fluorescence when PAb anti-7S was used, whereas with PAb anti-type IV, fluorescence was found almost exclusively on the surface of filamentous forms. A patched fluorescent pattern rather than a homogenous confluent fluorescence was observed in all cases. No fluorescent cells were observed with PAb anti-NC1. By Western immunoblotting, PAb anti-type IV cross-reacted primarily with a polypeptide of 37 kDa present in wall extracts obtained from intact cells of both growth forms by treatment with beta-mercaptoethanol, whereas PAb anti-7S recognized a major 58-kDa antigen also present in both extracts, along with some other high-molecular-mass (> 106-kDa) polydisperse species present only in the material released from blastoconidia with beta-mercaptoethanol. No reactive bands were observed when PAb anti-NC1 was used as a probe in Western immunoblotting experiments. The sensitivities or resistances to collagenase digestion of the different polypeptides that cross-reacted with PAbs anti-type IV and anti-7S suggest the existence of cell wall components in C. albicans that contain epitopes that mimic the collagenous domains of the type IV collagen molecule.