Talarico Lee A, Ingram Lonnie O, Maupin-Furlow Julie A
Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611-0700, USA1.
Microbiology (Reading). 2001 Sep;147(Pt 9):2425-2435. doi: 10.1099/00221287-147-9-2425.
Sarcina ventriculi grows in a remarkable range of mesophilic environments from pH 2 to pH 10. During growth in acidic environments, where acetate is toxic, expression of pyruvate decarboxylase (PDC) serves to direct the flow of pyruvate into ethanol during fermentation. PDC is rare in bacteria and absent in animals, although it is widely distributed in the plant kingdom. The pdc gene from S. ventriculi is the first to be cloned and characterized from a Gram-positive bacterium. In Escherichia coli, the recombinant pdc gene from S. ventriculi was poorly expressed due to differences in codon usage that are typical of low-G+C organisms. Expression was improved by the addition of supplemental codon genes and this facilitated the 136-fold purification of the recombinant enzyme as a homo-tetramer of 58 kDa subunits. Unlike Zymomonas mobilis PDC, which exhibits Michaelis-Menten kinetics, S. ventriculi PDC is activated by pyruvate and exhibits sigmoidal kinetics similar to fungal and higher plant PDCs. Amino acid residues involved in the allosteric site for pyruvate in fungal PDCs were conserved in S. ventriculi PDC, consistent with a conservation of mechanism. Cluster analysis of deduced amino acid sequences confirmed that S. ventriculi PDC is quite distant from Z. mobilis PDC and plant PDCs. S. ventriculi PDC appears to have diverged very early from a common ancestor which included most fungal PDCs and eubacterial indole-3-pyruvate decarboxylases. These results suggest that the S. ventriculi pdc gene is quite ancient in origin, in contrast to the Z. mobilis pdc, which may have originated by horizontal transfer from higher plants.
胃八叠球菌能在pH值为2至10的广泛嗜温环境中生长。在酸性环境（乙酸在此环境中有毒）中生长时，丙酮酸脱羧酶（PDC）的表达有助于在发酵过程中将丙酮酸导向生成乙醇。PDC在细菌中很少见，在动物中不存在，尽管它在植物界广泛分布。来自胃八叠球菌的pdc基因是第一个从革兰氏阳性细菌中克隆和鉴定的。在大肠杆菌中，由于低G+C含量生物体典型的密码子使用差异，来自胃八叠球菌的重组pdc基因表达不佳。通过添加补充密码子基因提高了表达，这有助于将重组酶作为58 kDa亚基的同型四聚体进行136倍的纯化。与呈现米氏动力学的运动发酵单胞菌PDC不同，胃八叠球菌PDC被丙酮酸激活，并呈现出类似于真菌和高等植物PDC的S形动力学。真菌PDC中参与丙酮酸变构位点的氨基酸残基在胃八叠球菌PDC中保守，这与机制的保守性一致。推导氨基酸序列的聚类分析证实，胃八叠球菌PDC与运动发酵单胞菌PDC和植物PDC相距甚远。胃八叠球菌PDC似乎很早就从一个共同祖先分化出来，这个共同祖先包括大多数真菌PDC和真细菌吲哚-3-丙酮酸脱羧酶。这些结果表明，胃八叠球菌的pdc基因起源非常古老，这与运动发酵单胞菌的pdc基因形成对比，后者可能是通过从高等植物水平转移而起源的。
