Biogenesis process of quinohemoprotein aminedehydrogenase accompanying multi-step posttranslational modification reactions

与大多数由水溶性维生素生物合成的普通辅因子不同，肽基内置辅因子是通过同源酶蛋白的翻译后修饰而产生的。在本研究中，我们重点研究了一种含有半胱氨酸色氨酸对苯二酚(CTQ)的内置含醌辅因子的酶--藜麦血蛋白胺脱氢酶(QHNDH)。革兰氏阴性菌中编码QHNDH的结构基因与邻近的几个基因共同构成一个多顺反子操纵子，统称为QHP。(1)我们已经鉴定出三个外周基因qhpFGR，它们也是QHNDH生物发生所必需的。(2)我们对QhpE的功能进行了分析，发现QhpE是一种非常罕见的酶，它几乎以一次性的方式切割底物。(3)只有在厌氧条件下进行纯化和处理，我们才能成功地利用过量生产的重组QhpD在体外形成硫醚交联。

Peptidyl built-in cofactors are produced by posttranslational modification of the cognate enzyme proteins, unlike ordinary cofactors which are mostly bio-synthesized from water soluble vitamins. In this study, we focused on a built-in quinone cofactor-containing enzyme, quinohemoprotein amine dehydrogenase (QHNDH) that contains cysteine tryptophyl quinone (CTQ). The structural genes encoding QHNDH in Gram-negative bacteria constitute a polycistronic operon together with several nearby genes, which are collectively termed qhp. (1) We have identified three peripheral genes, qhpFGR, that are also absolutely required for the QHNDH biogenesis. (2) We have analyzed the function of QhpE and revealed that QhpE is an extremely unusual protease that cleaves its substrate nearly in a disposable manner. (3) We have succeeded in in vitro formation of thioether cross-links using overproduced recombinant QhpD only if it is purified and handled under anaerobic conditions.