Schwedock Julie, Harmer Tara L, Scott Kathleen M, Hektor Harm J, Seitz Angelica P, Fontana Matthew C, Distel Daniel L, Cavanaugh Colleen M
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Arch Microbiol. 2004 Sep;182(1):18-29. doi: 10.1007/s00203-004-0689-x. Epub 2004 Jul 28.
Chemoautotrophic endosymbionts residing in Solemya velum gills provide this shallow water clam with most of its nutritional requirements. The cbb gene cluster of the S. velum symbiont, including cbbL and cbbS, which encode the large and small subunits of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO), was cloned and expressed in Escherichia coli. The recombinant RubisCO had a high specific activity, approximately 3 micromol min(-1) mg protein (-1), and a KCO2 of 40.3 microM. Based on sequence identity and phylogenetic analyses, these genes encode a form IA RubisCO, both subunits of which are closely related to those of the symbiont of the deep-sea hydrothermal vent gastropod Alviniconcha hessleri and the photosynthetic bacterium Allochromatium vinosum. In the cbb gene cluster of the S. velum symbiont, the cbbLS genes were followed by cbbQ and cbbO, which are found in some but not all cbb gene clusters and whose products are implicated in enhancing RubisCO activity post-translationally. cbbQ shares sequence similarity with nirQ and norQ, found in denitrification clusters of Pseudomonas stutzeri and Paracoccus denitrificans. The 3' region of cbbO from the S. velum symbiont, like that of the three other known cbbO genes, shares similarity to the 3' region of norD in the denitrification cluster. This is the first study to explore the cbb gene structure for a chemoautotrophic endosymbiont, which is critical both as an initial step in evaluating cbb operon structure in chemoautotrophic endosymbionts and in understanding the patterns and forces governing RubisCO evolution and physiology.
生活在维氏索足蛤鳃中的化能自养内共生体为这种浅水蛤提供了大部分营养需求。维氏索足蛤共生体的cbb基因簇，包括编码固碳酶1,5-二磷酸核酮糖羧化酶/加氧酶（RubisCO）大亚基和小亚基的cbbL和cbbS，被克隆并在大肠杆菌中表达。重组RubisCO具有较高的比活性，约为3微摩尔·分钟⁻¹·毫克蛋白⁻¹，二氧化碳的米氏常数（KCO₂）为40.3微摩尔。基于序列同一性和系统发育分析，这些基因编码一种IA型RubisCO，其两个亚基与深海热液喷口腹足动物赫氏阿尔文螺和光合细菌葡萄酒色嗜盐菌的共生体亚基密切相关。在维氏索足蛤共生体的cbb基因簇中，cbbLS基因之后是cbbQ和cbbO，它们存在于一些但不是所有的cbb基因簇中，其产物在翻译后增强RubisCO活性。cbbQ与施氏假单胞菌和反硝化副球菌反硝化簇中的nirQ和norQ具有序列相似性。维氏索足蛤共生体cbbO的3'区域，与其他三个已知的cbbO基因一样，与反硝化簇中norD的3'区域具有相似性。这是首次探索化能自养内共生体cbb基因结构的研究，这对于评估化能自养内共生体中cbb操纵子结构以及理解控制RubisCO进化和生理学的模式及因素至关重要。
