The Structure and Function of Candida albicans Cell Wall

Abstract

The wall and outer surface of pathogenic fungi is involved in adhesion and cell shape maintenance, and acts as a barrier to metabolites and drugs. In addition the cell wall contains immunogenic determinants, immunomodulators and secreted enzymes. The cell wall of C. albicans comprises some 30% of the dry weight of the cell and is composed predominantly of mannoproteins and β-glucans with small quantities of chitin, protein and lipid. Transmission electronmicroscopy of the wall reveals a number of different layers; the thickness and number of these layers varies during germ-tube formation and the cell cycle. The outer fuzzy layer of the wall contains receptors that bind plastic, laminin, fibrinogen, and C3 fragments of complement. The β1, 3 and β1, 6 glucans and chitin are the polymers which endow rigidity on the cell wall. These polymers form a microfibrillar scaffolding upon which other macromolecules, particularly mannoproteins are bound.The wall mannoproteins are highly branched polysaccharides primarily composed of mannose units attached to protein through a G 1 cNac dimer bridge and asparagine. There are also smaller numbers of 0-linked mannoproteins where the mannose units are attached to protein through serine and threonine residues. The mannoproteins have a backbone of α-1, 6 linked mannose units to which side chains of mannoses attach via α-1, 2-and occasionally α-1, 3 bonds. The side chains are the major antigenic determinants and the A and B serotypes are distinguished by differences between these side chains. A model for cell wall growth and development will is described.