Significant amounts of
enolase-a cytosolic
enzyme involved in the glycolysis pathway-are exposed on the cell surface of Candida yeast. It has been hypothesized that this exposed
enolase form contributes to
infection-related phenomena such as fungal adhesion to human tissues, and the activation of fibrinolysis and extracellular matrix degradation. The aim of the present study was to characterize, in structural terms, the
protein-
protein interactions underlying these moonlighting functions of
enolase. The tight binding of human
vitronectin,
fibronectin and
plasminogen by purified C. albicans and C. tropicalis enolases was quantitatively analyzed by surface plasmon resonance measurements, and the dissociation constants of the formed complexes were determined to be in the 10-7-10-8 M range. In contrast, the binding of human
proteins by the S.cerevisiae
enzyme was much weaker. The chemical cross-linking method was used to map the sites on
enolase molecules that come into direct contact with human
proteins. An internal motif 235DKAGYKGKVGIAMDVASSEFYKDGK259 in C. albicans
enolase was suggested to contribute to the binding of all three human
proteins tested. Models for these interactions were developed and revealed the sites on the
enolase molecule that bind human
proteins, extensively overlap for these
ligands, and are well-separated from the catalytic activity center.