Identification of cellulose synthase(s) in higher plants: sequence analysis of processive β-glycosyltransferases with the common motif ‘D, D, D35Q(R,Q)XRW’

Author： SAXENA INDER BROWN R.

Publisher： Springer Publishing Company

ISSN： 0969-0239

Source： Cellulose, Vol.4, Iss.1, 1997-04, pp. : 33-49

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Abstract

More than ten β-glycosyltransferases are now recognized that have limitedsimilarity to the amino acid sequence of cellulose synthase fromAcetobacter xylinum. Using hydrophobic cluster analysis (HCA), werecently identified two domains and putative catalytic residuesin the processive β-glycosyltransferases. In this study, wehave found expressed sequence tags (ESTs) from higher plants(Arabidopsis thaliana, Brassica campestris, and Oryza sativa)that exhibit a limited sequence similarity to the A. xylinumcellulose synthase. These ESTs contain some of the conservedresidues identified in the processive β-glycosyltransferases. Complete sequencing of an EST clone(T88271) from A. thaliana led to the identification of all theconserved residues in the derived truncated polypeptide whichappears to be part of a putative cellulose synthase. Sequencecomparison of proteins with known function and severalunidentified proteins have the ‘D, D, D35Q(R,Q)XRW’ motif whichis considered a strong predictor for β-glycosyltransferasesthat includes, among other proteins, cellulose and chitinsynthases. The first two conserved aspartic acid residues in thismotif were analysed by site-directed mutagenesis, and theirreplacement by another amino acid led to a loss of cellulosesynthase activity in A. xylinum, suggesting that they areessential for enzyme activity. A correlation between the secondresidue (R or Q) in the Q(R,Q)XRW sequence and the synthesis of along glucan chain (polysaccharide) or a short glucan chain(oligosaccharide) suggests that this residue may be involved inthe degree of processivity