控制氧化还原电位的flavodoxin beijerinckii:梭状芽胞杆菌构象变化的作用。
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路德维希ML, Pattridge KA, Metzger AL Dixon MM, Eren M,冯Y,斯文森RP
控制氧化还原电位的flavodoxin beijerinckii:梭状芽胞杆菌构象变化的作用。
生物化学,1997年2月11日,36 (6):1259 - 80。
- PubMed ID
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9063874 (在PubMed]
- 文摘
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x射线分析野生型和突变flavodoxins beijerinckii表明梭状芽胞杆菌肽Gly57-Asp58的构象,在弯曲FMN异咯嗪环附近,与氧化态的FMN辅基。Gly-Asp肽可能采用的三种构象:反式O-up的羰基氧Gly57 (O57)指向黄素环;反式o分解,O57点远离黄素;和cis o分解。这些矫形器之间的互变现象与氧化还原的黄素可以调节绑定FMN的氧化还原电位。半醌和减少形式的蛋白质,Gly57-Asp58肽采用反式O-up构象和接受一个氢键黄素N5H[史密斯,W W。伯内特,r . M。,亲爱的,g D。&路德维希,m·l·j·摩尔(1977)。杂志。117年,195 - 225;路德维格·m·L。& Luschinsky c . l .(1992)在化学和生物化学的黄素酶III(穆勒,F。(Ed)页427 - 466,CRC出版社,佛罗里达州波卡拉顿的]。本文分析报告确认,在晶体的野生型氧化c beijerinckii flavodoxin, Gly57-Asp58肽采用o分解方向和异构化的顺式构象。 This cis form is preferentially stabilized in the crystals by intermolecular hydrogen bonding to Asn137. Structures for the mutant Asn137Ala indicate that a mixture of all three conformers, mostly O-down, exists in oxidized C. beijerinckii flavodoxin in the absence of intermolecular hydrogen bonds. Redox potentials have been manipulated by substitutions that alter the conformational energies of the bend at 56M-G-D-E. The mutation Asp58Pro was constructed to study a case where energies for cis-trans conversion would be different from that of wild type. Intermolecular interactions with Asn137 are precluded in the crystal, yet Gly57-Pro58 is cis, and O-down, when the flavin is oxidized. Reduction of the flavin induces rearrangement to the trans O-up conformation. Redox potential shifts reflect the altered energies associated with the peptide rearrangement; E(ox/sq) decreases by approximately 60 mV (1.3 kcal/mol). Further, the results of mutation of Gly57 agree with predictions that a side chain at residue 57 should make addition of the first electron more difficult, by raising the energy of the O-up conformer that forms when the flavin is reduced to its semiquinone state. The ox/sq potentials in the mutants Gly57Ala, Gly57Asn, and Gly57Asp are all decreased by approximately 60 mV (1.3 kcal/mol). Introduction of the beta-branched threonine side chain at position 57 has much larger effects on the conformations and potentials. The Thr57-Asp58 peptide adopts a trans O-down conformation when the flavin is oxidized; upon reduction to the semiquinone, the 57-58 peptide rotates to a trans O-up conformation resembling that found in the wild-type protein. Changes in FMN-protein interactions and in conformational equilibria in G57T combine to decrease the redox potential for the ox/sq equilibrium by 180 mV (+4.0 kcal/mol) and to increase the sq/hq potential by 80 mV (-1.7 kcal/mol). A thermodynamic scheme is introduced as a framework for rationalizing the properties of wild-type flavodoxin and the effects of the mutations.