Xylan backbone synthesis, unlike that of the other hemicelluloses, is not mediated by any cellulose synthase-like proteins. Instead, xylan synthase is responsible for backbone synthesis, facilitating the addition of xylose. Several genes for xylan synthases have been identified. Several other enzymes are utilized for the addition and modification of the side-chain units of xylan, including glucuronosyltransferase (which adds [glucuronic acid units), xylosyltransferase (which adds additional xylose units), arabinosyltransferase (which adds arabinose), methyltransferase (responsible for methylation), and acetyltransferase] (responsible for acetylation). Given that mixed-linkage glucan is a non-branched homopolymer of glucose, there is no side-chain synthesis, only the addition of glucose to the backbone in two linkages, β1-3 and β1-4. Backbone synthesis is mediated by enzymes in cellulose synthase-like protein families F and H (CSLF and CSLH), specifically glucan synthase. Several forms of glucan synthase from CSLF and CSLH have been identified. All of them are responsible for addition of glucose to the backbone and all are capable of producing both β1-3 and β1-4 linkages, however, it is unknown how much each specific enzyme contributes to the distribution of β1-3 and β1-4 linkages.
xylan backbone synthesis unlike that of the other hemicelluloses is not mediated by any cellulose synthase-like proteins instead xylan synthase is responsible for backbone synthesis facilitating the addition of xylose several genes for xylan synthases have been identified several other enzymes are utilized for the addition and modification of the side-chain units of xylan including glucuronosyltransferase (which adds [glucuronic acid units) xylosyltransferase (which adds additional xylose units) arabinosyltransferase (which adds arabinose) methyltransferase (responsible for methylation) and acetyltransferase] (responsible for acetylation) given that mixed-linkage glucan is a non-branched homopolymer of glucose there is no side-chain synthesis only the addition of glucose to the backbone in two linkages β1-3 and β1-4 backbone synthesis is mediated by enzymes in cellulose synthase-like protein families f and h (cslf and cslh) specifically glucan synthase several forms of glucan synthase from cslf and cslh have been identified all of them are responsible for addition of glucose to the backbone and all are capable of producing both β1-3 and β1-4 linkages however it is unknown how much each specific enzyme contributes to the distribution of β1-3 and β1-4 linkages