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首页> 外文期刊>Biochemistry >Structure, function, and temperature sensitivity of directed, random mutants at proline 76 and glycine 77 in Omega-loop D of yeast iso-1-cytochrome c
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Structure, function, and temperature sensitivity of directed, random mutants at proline 76 and glycine 77 in Omega-loop D of yeast iso-1-cytochrome c

机译：酵母iso-1-cytochrome c的Omega-D环中脯氨酸76和甘氨酸77上有向随机突变体的结构，功能和温度敏感性

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摘要

Residues 75-78 form a tight turn within Omega-loop D in Saccharomyces cerevisiae iso-1-cytochrome c. Directed, random mutagenesis of invariant residues proline 76 and glycine 77 in this rum were analyzed for the in vivo functionality and level of protein within the cell. All proteins, except Pro76Val, also exhibit a significant decrease in intracellular cytochrome c levels, ranging from 15% to 80% of wild type. Furthermore, all isolated mutant strains, except the one expressing Pro76Val, exhibit a significant decrease in growth on lactate medium, suggesting that the variant cytochromes are much less functional than, wild type. This requirement for protein function is clearly the cause for the strict invariance of these residues in eukaryotic cytochromes c. Seven proteins with mutations just at Pro76 were purified and studied by circular dichroism spectroscopy. All proteins with mutations at Pro76 exhibit melting temperatures about 7 degrees C less than that of the wild-type protein, suggesting that mutation of Pro76 affects the entropy of the denatured state. It is proposed that the functional significance of Pro76 and Gly77 is the requirement for a type II (beta(gamma L)) beta-turn in this loop, the conformation of which requires a glycine at the third position, and that a change occurs in this turn conformation upon a change in the redox state of the protein. [References: 97]
机译：酿酒酵母异1细胞色素c中的残基75-78在欧米茄环D中形成一个紧密的转弯。针对该朗姆酒中恒定残基脯氨酸76和甘氨酸77的定向，随机诱变，分析了体内功能和细胞内蛋白质的水平。除Pro76Val外，所有蛋白质的细胞内细胞色素c水平也显着降低，范围为野生型的15％至80％。此外，除表达Pro76Val的菌株外，所有分离的突变菌株在乳酸培养基上的生长均显着降低，这表明变异的细胞色素的功能远低于野生型。对蛋白质功能的这种要求显然是真核细胞色素c中这些残基严格不变的原因。纯化了仅在Pro76处具有突变的7种蛋白质，并通过圆二色谱法对其进行了研究。所有在Pro76处发生突变的蛋白质均比野生型蛋白质的熔化温度低约7摄氏度，这表明Pro76的突变会影响变性状态的熵。提出Pro76和Gly77的功能重要性是在该环中需要进行II型（β（γL））β转角的作用，其构象在第三位置需要一个甘氨酸，并且在其中发生变化。这种转变构象取决于蛋白质氧化还原状态的变化。 [参考：97]

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