Zufferey R, Hennecke H, Thöny-Meyer L
Mikrobiologisches Institut, Eidgenossische Technische Hochschule, Zürich, Switzerland.
FEBS Lett. 1997 Jul 21;412(1):75-8. doi: 10.1016/s0014-5793(97)00746-1.
The monoheme and diheme c-type cytochromes FixO and FixP are two of the subunits of the respiratory cbb3-type oxidase of Bradyrhizobium japonicum. The cysteines of the respective heme C binding motifs CXXCH were changed to serines by site-directed mutagenesis, which led to inactive oxidases in all mutants. Western blot analyses showed that an intact heme binding site in the FixO polypeptide is a prerequisite not only for the synthesis of holo-FixO protein but also for the formation of the entire cbb3-type oxidase complex. Both heme binding sites of FixP were essential for maturation and assembly of this subunit. It was not possible to create stable FixP variants that contained only one heme C.
单血红素和双血红素c型细胞色素FixO和FixP是日本慢生根瘤菌呼吸型cbb3型氧化酶的两个亚基。通过定点诱变将各自血红素C结合基序CXXCH中的半胱氨酸替换为丝氨酸，导致所有突变体中的氧化酶均无活性。蛋白质免疫印迹分析表明，FixO多肽中完整的血红素结合位点不仅是全酶FixO蛋白合成的前提条件，也是整个cbb3型氧化酶复合物形成的前提条件。FixP的两个血红素结合位点对于该亚基的成熟和组装至关重要。不可能产生仅含有一个血红素C的稳定FixP变体。
