十字花科黑腐病菌纤维素酶主效基因XC0639 CBD结构域功能的分析

Functional characterization of CBD domain of the major cellulase gene XC0639 in Xanthomonas campestris pv.campestris

十字花科黑腐病菌(Xanthomonas campestris pv. campestris,Xcc)几乎能引起所有十字花科植物产生黑腐病[1]。该菌是研究植物与病原微生物互作的模式菌株之一[2]。植物病原菌在侵染宿主植物时需要先降解植物细胞的细胞壁,纤维素和半纤维素是细胞壁的主要成分。纤维素酶是降解纤维素生成葡萄糖的一类复合酶,主要由内切葡聚糖酶、外切葡聚糖酶以及β-葡萄糖苷酶3类酶组成,三者作用方式不同,但能协同催化水解纤维素[3]。

Xanthomonas campestris pv.campestris(Xcc) is an important pathogen that infects cruciferous plants.Extracellular cellulases are important for full virulence of Xcc.In Xcc 8004,nine genes were annotated to encode extracellular cellulases and one of them(XC0639) was the major cellulase gene.This work studied the effect of the bioinformatically predicted cellulase binding domain(CBD) of XC0639 on enzyme activity by constructing XC0639 CBD deletion mutant named D0639(CBD) and a complementary strain of D0639(CBD)named C0639(CBD).Interestingly,there was no significant difference among the cellulase activities produced by D0639(CBD),C0639(CBD),and the wild-type strain 8004,suggesting that the predicted CBD is not involved in the enzyme activity of XC0639.This contention was supported by the results showing that the cellulase activities exhibited by a mutant(D9) with deletion of all 9 annotated cellulase genes,D9 carrying an entire XC0639 in trans,D9 carrying an XC0639 lacking its CBD in trans,and the wild type strain 8004 were not significantly different.This finding provides a base for further study of the catalytic mechanism of the major cellulase XC0639 in Xcc.