Green Dixy E, DeAngelis Paul L
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, 940 Stanton L. Young Blvd., BMSB 853,Oklahoma City, OK73126-0901, USA.
Glycobiology. 2017 May 1;27(5):469-476. doi: 10.1093/glycob/cwx008.
Glycosaminoglycans (GAGs) are known to be present in all animals as well as some pathogenic microbes. Chondroitin sulfate is the most abundant GAG in mammals where it has various structural and adhesion roles. The Gram-negative bacteria Pasteurella multocida Type F and Escherichia coli K4 produce extracellular capsules composed of unsulfated chondroitin or a fructosylated chondroitin, respectively. Such polysaccharides that are structurally related to host molecules do not generally provoke a strong antibody response thus are thought to be employed as molecular camouflage during infection. We observed a sequence from the photosynthetic green sulfur bacteria, Chlorobium phaeobacteroides DSM 266, which was very similar (~62% identical) to the open reading frames of the known bifunctional chondroitin synthases (PmCS and KfoC); some segments are strikingly conserved amongst the three proteins. Recombinant E. coli-derived Chlorobium enzyme preparations were found to possess bona fide chondroitin synthase activity in vitro. This new catalyst, CpCS, however, has a more promiscuous acceptor usage than the prototypical PmCS, which may be of utility in novel chimeric GAG syntheses. The finding of such a similar chondroitin synthase enzyme in C. phaeobacteroides is unexpected for several reasons including (a) a free-living nonpathogenic organism should not "need" an animal self molecule for protection, (b) the Proteobacteria and the green sulfur bacterial lineages diverged ~2.5-3 billion years ago and (c) the ecological niches of these bacteria are not thought to overlap substantially to facilitate horizontal gene transfer. CpCS provides insight into the structure/function relationship of this class of enzymes.
已知糖胺聚糖（GAGs）存在于所有动物以及一些致病微生物中。硫酸软骨素是哺乳动物中含量最丰富的GAG，在其中具有多种结构和黏附作用。革兰氏阴性菌多杀巴斯德氏菌F型和大肠杆菌K4分别产生由未硫酸化的软骨素或果糖基化软骨素组成的细胞外荚膜。这种在结构上与宿主分子相关的多糖通常不会引发强烈的抗体反应，因此被认为在感染过程中被用作分子伪装。我们观察到来自光合绿硫细菌绿褐绿菌DSM 266的一个序列，它与已知的双功能软骨素合酶（PmCS和KfoC）的开放阅读框非常相似（约62%相同）；三个蛋白质中的一些片段显著保守。发现重组大肠杆菌来源的绿褐绿菌酶制剂在体外具有真正的软骨素合酶活性。然而，这种新的催化剂CpCS比典型的PmCS具有更广泛的受体使用范围，这可能在新型嵌合GAG合成中有用。在绿褐绿菌中发现如此相似的软骨素合酶出乎意料，原因有几个，包括（a）一种自由生活的非致病生物不应该“需要”动物自身分子来保护，（b）变形菌门和绿硫细菌谱系在约25 - 30亿年前就分化了，以及（c）这些细菌的生态位被认为没有实质性重叠以促进水平基因转移。CpCS为这类酶的结构/功能关系提供了见解。
