Molecular bases of adhesion of Candida albicans

The purpose of this review is to focus on the location and the adhesion activity of the protein (peptide) and the mannan moieties of the mannoprotein in the outer surface of the Candida albicans cell wall. A macromolecule of the mannoprotein located on the outermost surface is undoubtedly a strong adhesin comprising several adhesion molecules including protein and mannan. Mannoproteins can be divided into two classes, higher molecular weight peptidomannans (260 kDa) and lower molecular weight mannoproteins (50-66 kDa), both of which consist of similar mannans and disparate proteins or peptides which have distinct adhesion specificities. The protein moiety of mannoprotein can be divided functionally into two groups, lectin-like proteins and proteins recognizing arginine-glycine-aspartic acid (RGD) ligands. The latter proteins are further subdivided into two groups, CR2/CR3-like proteins and proteins binding extracellular matrix (ECM) proteins. Hydrophobicity of the cell surface of C. albicans influences adhesion of the organisms to epithelial cells. Degree of glycosylation of cell surface mannoproteins that affect yeast cell surface hydrophobicity affects adhesion of C. albicans to epithelial cells. The hydrophobic proteins may have low levels of glycosylation, and changes in glycosylation may determine exposure of hydrophobic protein regions at the cell surface. The serotype A-specific oligosaccharide of antigen 6 (pentaose or hexaose of mannan moiety) has been shown to exhibit marked adhesion ability for epithelial cells, and mannotetraose related to antigenic factor 5 which is present in both serotypes A and B showed adhesive activity for tissue macrophages. Proteinoceous adhesins of C. albicans are expressed preferably on the mycelial form. It is suggested that several of the adhesion molecules of C. albicans described above appear to complementarily utilize multiple adhesion mechanisms.