Identification of a Glucan-Associated Enolase as a Main Cell Wall Protein of Candida albicans and an Indirect Target of Lipopeptide Antimycotics

Abstract

Growth-subinhibitory nonlytic doses of cilofungin (a lipopeptide antibiotic affecting (1,3)-β-d-glucan synthesis) inhibited the incorporation of 46- to 48-kDa glucan-associated (46K) protein into the growing cell wall of Candida albicans. The purified 46K protein constituent strongly reacted with a monoclonal antibody against enolase, a major cytoplasmic enzyme of the fungus. In addition, two internal fragments of 12- and IS-amino acid residues from a tryptic digest of 46K protein showed 100% identity with amino acids in positions 34–45 and 66–80 of enolase. By immunoelectron microscopy with polyclonal and monoclonal anti-enolase antibodies, the 46K protein was clearly detected in the inner layers of the fungal cell wall. Thus, consistent with the proposed immunogenic and diagnostic roles of enolase in candidiasis, biochemical, immunochemical, and ultrastructural evidence strongly suggest that the cilofungin-susceptible 46K protein is a cell wall-associated form of this enzyme.