Abbott D Wade, Boraston Alisdair B
Biochemistry and Microbiology, University of Victoria, PO Box 3055 STN CSC, Victoria, British Columbia V8W 3P6, Canada.
Microbiol Mol Biol Rev. 2008 Jun;72(2):301-16, table of contents. doi: 10.1128/MMBR.00038-07.
Pectin is a structural polysaccharide that is integral for the stability of plant cell walls. During soft rot infection, secreted virulence factors from pectinolytic bacteria such as Erwinia spp. degrade pectin, resulting in characteristic plant cell necrosis and tissue maceration. Catabolism of pectin and its breakdown products by pectinolytic bacteria occurs within distinct cellular environments. This process initiates outside the cell, continues within the periplasmic space, and culminates in the cytoplasm. Although pectin utilization is well understood at the genetic and biochemical levels, an inclusive structural description of pectinases and pectin binding proteins by both extracellular and periplasmic enzymes has been lacking, especially following the recent characterization of several periplasmic components and protein-oligogalacturonide complexes. Here we provide a comprehensive analysis of the protein folds and mechanisms of pectate lyases, polygalacturonases, and carbohydrate esterases and the binding specificities of two periplasmic pectic binding proteins from Enterobacteriaceae. This review provides a structural understanding of the molecular determinants of pectin utilization and the mechanisms driving catabolite selectivity and flow through the pathway.
果胶是一种结构多糖，对植物细胞壁的稳定性至关重要。在软腐病感染期间，诸如欧文氏菌属等果胶分解细菌分泌的毒力因子会降解果胶，导致典型的植物细胞坏死和组织浸解。果胶分解细菌对果胶及其分解产物的分解代谢发生在不同的细胞环境中。这个过程始于细胞外，在周质空间继续进行，并在细胞质中达到高潮。尽管在基因和生化水平上对果胶利用已了解得很清楚，但一直缺乏对胞外酶和周质酶所作用的果胶酶和果胶结合蛋白的全面结构描述，尤其是在最近对几种周质成分和蛋白质 - 低聚半乳糖醛酸复合物进行表征之后。在此，我们对果胶酸裂解酶、多聚半乳糖醛酸酶和碳水化合物酯酶的蛋白质折叠及作用机制以及来自肠杆菌科的两种周质果胶结合蛋白的结合特异性进行了全面分析。本综述提供了对果胶利用分子决定因素以及驱动分解代谢物选择性和流经该途径机制的结构理解。
