Zufferey R, Thöny-Meyer L, Hennecke H
Mikrobiologisches Institut, Eidgenössische Technische Hochschule, Zürich, Switzerland.
FEBS Lett. 1996 Oct 7;394(3):349-52. doi: 10.1016/0014-5793(96)00982-9.
In subunit I (FixN) of the Bradyrhizobium japonicum cbb3-type oxidase, only five instead of the normal six strictly conserved histidines (H) could be unambiguously assigned as the putative heme or copper ligands. The ambiguity concerned H43 or H131 as the presumptive N-terminal ligands of the low-spin heme B. We report here that a H43A replacement had a wild-type phenotype, whereas the H131A mutant was defective in oxidase function and subunit assembly or stability, suggesting that H131 serves as the N-terminal low-spin heme ligand. Topological studies revealed that H131 resides on the periplasmic side of helix 2, where one of the low-spin heme ligands is normally found in conventional heme-copper oxidases.
在日本慢生根瘤菌cbb3型氧化酶的亚基I（FixN）中，只有五个而非正常的六个严格保守的组氨酸（H）能够被明确指定为假定的血红素或铜配体。不确定性涉及H43或H131作为低自旋血红素B的推定N端配体。我们在此报告，H43A替代具有野生型表型，而H131A突变体在氧化酶功能以及亚基组装或稳定性方面存在缺陷，这表明H131作为N端低自旋血红素配体。拓扑学研究表明，H131位于螺旋2的周质侧，在传统的血红素-铜氧化酶中，低自旋血红素配体之一通常位于此处。
