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首页> 外文期刊>Biochemistry >Conversion of the Escherichia coli Cytochrome b552 to an Archetype Cytochrome b:A Mutant with Bis-Histidine Ligation of Heme Iron
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Conversion of the Escherichia coli Cytochrome b552 to an Archetype Cytochrome b:A Mutant with Bis-Histidine Ligation of Heme Iron

机译：大肠杆菌细胞色素b552转化为原型细胞色素b：血红素铁双组氨酸连接的突变体

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摘要

A mutant of the Escherichia coli Cytochrome E552 has been created in which the heme-ligating methionine (Met) at position 7 has been replaced with a histidine (His) (M7H).This protein is a double mutant that also has the His 63 to asparagine (H63N) mutation,which removes a solvent-exposed His.While the H63N mutation has no measurable effect on the cytochrome,the M7H mutation converts the atypical His/Met heme ligation in cytochrome b_(562) to the classic cytochrome b-type bis-His ligation.This mutation has little effect on the K_d of heme binding but significantly reduces the chemical and thermal stability of the mutant cytochrome relative to the wild type (wt).Both proteins have similar absorbance (Abs) and electron paramagnetic resonance (EPR) properties characteristic of 6-coordinate low-spin heme.The Abs spectra of the oxidized and reduced bis-His cytochrome are slightly blue-shifted relative to the wt,and the a Abs band of ferrous M7H mutant is unusually split.The M7H mutation decreases the midpoint potential of the bound heme by 260 mV at pH 7 and considerably alters the pH dependence of the E_m,which becomes dominated by a single pK_(red) = 6.8.
机译：产生了一种大肠杆菌细胞色素E552的突变体，其中第7位的血红素连接蛋氨酸（Met）被组氨酸（His）（M7H）取代，该蛋白是双重突变体，也具有His 63至天冬酰胺（H63N）突变去除了溶剂暴露的His.H63N突变对细胞色素没有可测量的影响，M7H突变将细胞色素b_（562）中的非典型His / Met血红素血红素连接转化为经典的细胞色素b型bis-His连接。此突变对血红素结合的K_d影响不大，但相对于野生型（wt）却大大降低了突变型细胞色素的化学和热稳定性。两种蛋白的吸光度（Abs）和电子顺磁共振相似六坐标低自旋血红素的EPR）特性。氧化和还原的bis-His细胞色素的Abs光谱相对于wt呈蓝移，并且M7H亚铁突变体的Abs带异常分裂。突变dec在pH 7时可将结合血红素的中点电位提高260 mV，并极大地改变了E_m的pH依赖性，这主要由单个pK_（red）= 6.8决定。

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