Forms of chitin-polysaccharide cross-linking in the Coprinopsis cinerea stipe cell wall

The fungal cell wall provides the cell with enough strength to withstand turgor pressure and keeps adequate plasticity to extend the cell wall size under turgor pressure for cell growth. The cell walls of apical growing hyphae and budding growth yeast have been studied in detailed which share common components of chitin and β-1,3-glucan in their scaffold structures while other polysaccharide components vary on species. In contrast, the cell walls of elongating growth mushroom stipe remains poorly studied. This study explored that in addition to chitin, β-1,3-glucan with β-1,6-linkage branches, and β-1,6-glucan with β-1,3-linkage branches, the scaffold structure of C. cinerea cell wall also incorporated β-1,4-glucan, a component not previously reported in fungal cell walls. After converting chitin to chitosan, we identified three distinct forms of chitosan (chitin). The first was a free chitosan-β-glucan complex, in which chitosan was covalently linked to low molecular weight β-1,6-, β-1,3-, or β-1,4-glucan, which could be extracted using 10 % acetic acid. The second form consisted of chitosan-β-glucan complexes covalently linked to the β-1,4-glucan matrix polysaccharide via β-1,6-glucan, β-1,3-glucan, or β-1,4-glucan, which could be released from the cell wall by hydrolases hydrolysis. The third form involved the release of insoluble chitosan as chitooligosaccharides by chitosanase.