Lopez P, Lacks S A
Biology Department, Brookhaven National Laboratory, Upton, New York 11973.
J Bacteriol. 1993 Apr;175(8):2214-20. doi: 10.1128/jb.175.8.2214-2220.1993.
A protein encoded by sulD, one of four genes in a previously cloned folate biosynthetic operon of Streptococcus pneumoniae, had been shown to harbor 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase activity. This SulD protein was purified and shown now to harbor also dihydroneopterin aldolase activity. The bifunctional protein therefore catalyzes two successive steps in folate biosynthesis. The aldolase activity can be ascribed to the N-terminal domain of the SulD polypeptide, and the pyrophosphokinase activity can be ascribed to the C-terminal domain. Homologs of the dihydroneopterin aldolase domain were identified in other species, in one of which the domain was encoded as a separate polypeptide. The native SulD protein is a trimer or tetramer of a 31-kDa subunit, and it dissociated reversibly after purification. Dihydroneopterin aldolase activity required the multimeric protein, whereas pyrophosphokinase was expressed by the monomeric form. With purified SulD, the amount of 6-hydroxymethyl-7,8-dihydropterin product formed by the aldolase was proportional to the fourth power of the enzyme concentration, as expected for a reversibly dissociating tetramer. By identifying the gene encoding dihydroneopterin aldolase, this work extends our understanding of the molecular basis of the folate biosynthetic system common to many organisms.
sulD编码的一种蛋白质，是先前克隆的肺炎链球菌叶酸生物合成操纵子中四个基因之一，已被证明具有6 - 羟甲基 - 7,8 - 二氢蝶呤焦磷酸激酶活性。这种SulD蛋白被纯化，现在还显示具有二氢新蝶呤醛缩酶活性。因此，这种双功能蛋白催化叶酸生物合成中的两个连续步骤。醛缩酶活性可归因于SulD多肽的N端结构域，焦磷酸激酶活性可归因于C端结构域。在其他物种中鉴定出了二氢新蝶呤醛缩酶结构域的同源物，其中一个物种中该结构域被编码为一种单独的多肽。天然的SulD蛋白是一个31 kDa亚基的三聚体或四聚体，纯化后可逆解离。二氢新蝶呤醛缩酶活性需要多聚体蛋白，而焦磷酸激酶则由单体形式表达。对于纯化的SulD，醛缩酶形成的6 - 羟甲基 - 7,8 - 二氢蝶呤产物的量与酶浓度的四次方成正比，这与可逆解离的四聚体预期情况相符。通过鉴定编码二氢新蝶呤醛缩酶的基因，这项工作扩展了我们对许多生物体共有的叶酸生物合成系统分子基础的理解。
