Candidacidal activity of myeloperoxidase: characterization of myeloperoxidase-yeast complex formation.

We have previously demonstrated the ability of human neutrophil myeloperoxidase to bind to cell wall mannan polysaccharide isolated from Candida albicans. This binding capacity provides for association of the enzyme with target yeast which is essential for efficient candidacidal activity. In this report, we further consider the role of the mannan-binding property of myeloperoxidase in the candidacidal activity of the enzyme. Solubilized mannan antagonizes binding of the enzyme to yeast, suggesting that mannan may be a primary component of the fungal cell wall which serves as a target for binding of myeloperoxidase. Myeloperoxidase is shown to form complexes with both solubilized mannan and Candida yeast, with Kds of 0.97 x 10(-5) M and 1.2 x 10(-5) M, respectively. The interaction between myeloperoxidase and mannan does not allow the enzyme to readily dissociate from the surface of target yeast. As a result, the enzyme may be unable to dissociate from dead yeast to become available for binding to additional fungal targets.