Mittenhuber G
Institut für Mikrobiologie und Molekularbiologie, Ernst-Moritz-Arndt-Universität, Greifswald, Germany.
J Mol Microbiol Biotechnol. 2001 Jan;3(1):1-20.
Vitamin B6 in its active form pyridoxal phosphate is an essential coenzyme of many diverse enzymes. Biochemistry, enzymology and genetics of de novo vitamin B6 biosynthesis have been primarily investigated in Escherichia coli. Database searches revealed that the key enzymes involved in ring closure of the aromatic pyridoxin ring (PdxA; PdxJ) are present mainly in genomes of bacteria constituting the gamma subdivision of proteobacteria. The distribution of DXS, a transketolase-like enzyme involved in vitamin B6 biosynthesis as well as in thiamine and isoprenoid biosynthesis and the distribution of vitamin B6 modifying enzymes (PdxH: oxidase; PdxK: kinase) was also analyzed. These enzymes are also present in the genomes of animals. Two recent papers (Ehrenshaft et al., 1999, Proc. Natl. Acad. Sci. USA. 96: 9374-9378; Osmani et al., 1999, J. Biol. Chem. 274: 23565-23569) show the involvement of an extremely conserved protein (a member of the UPF0019 or SNZ family) found in all three domains of life (bacteria, archaea, eukarya) in an alternative vitamin B6 biosynthesis pathway. Members of this family were previously identified as a stationary phase inducible protein in yeast, as an ethylene responsible protein in plants and in a marine sponge, as a singlet oxygen resistance protein in Cercospora nicotianae and as a cumene hydroperoxide and H2O2 inducible protein in Bacillus subtilis. In yeast, the SNZ protein interacts with another protein called SNO which also represents a member of a highly conserved protein family (called UPF0030 or SNO family). Phylogenetic trees for the DXS, PdxA, PdxJ, PdxH, PdxK, SNZ and SNO protein families are presented and possible implications of the two different vitamin B6 biosynthesis pathways in cellular metabolism are discussed. A radically different view of bacterial evolution (Gupta, 2000, Crit. Rev. Microbiol. 26: 111-131) which proposes a linear rather than a treelike evolutionary relationship between procaryotic species indicates that the gamma subdivision of proteobacteria represents the most recently evolved bacterial lineage. This proposal might help to explain why the PdxA/PdxJ pathway is largely restricted to this subdivision.
维生素B6的活性形式磷酸吡哆醛是多种不同酶的必需辅酶。维生素B6从头生物合成的生物化学、酶学和遗传学主要在大肠杆菌中进行了研究。数据库搜索显示，参与芳香族吡哆醇环闭环的关键酶（PdxA；PdxJ）主要存在于构成变形菌门γ亚群的细菌基因组中。还分析了参与维生素B6生物合成以及硫胺素和类异戊二烯生物合成的转酮醇酶样酶DXS的分布，以及维生素B6修饰酶（PdxH：氧化酶；PdxK：激酶）的分布。这些酶也存在于动物基因组中。最近的两篇论文（Ehrenshaft等人，1999年，《美国国家科学院院刊》。96：9374 - 9378；Osmani等人，1999年，《生物化学杂志》。274：23565 - 23569）表明，在生命的所有三个域（细菌、古细菌、真核生物）中发现的一种极其保守的蛋白质（UPF0019或SNZ家族的成员）参与了另一条维生素B6生物合成途径。该家族的成员先前在酵母中被鉴定为一种稳定期诱导蛋白，在植物和一种海洋海绵中被鉴定为一种与乙烯相关的蛋白，在烟草尾孢菌中被鉴定为一种单线态氧抗性蛋白，在枯草芽孢杆菌中被鉴定为一种异丙苯过氧化氢和H2O2诱导蛋白。在酵母中，SNZ蛋白与另一种名为SNO的蛋白相互作用，SNO也代表一个高度保守的蛋白家族（称为UPF0030或SNO家族）的成员。给出了DXS、PdxA、PdxJ、PdxH、PdxK、SNZ和SNO蛋白家族的系统发育树，并讨论了两种不同的维生素B6生物合成途径在细胞代谢中的可能影响。一种关于细菌进化的截然不同的观点（Gupta，2000年，《微生物学评论》。26：111 - 131）提出原核生物物种之间是线性而非树状的进化关系，这表明变形菌门的γ亚群代表了最近进化的细菌谱系。这一观点可能有助于解释为什么PdxA/PdxJ途径在很大程度上限于这个亚群。
