Electrostatic effects of surface acidic amino acid residues on the oxidation-reduction potentials of the flavodoxin from Desulfovibrio vulgaris (Hildenborough).
Electrostatic effects of surface acidic amino acid residues on the oxidation-reduction potentials of the flavodoxin from Desulfovibrio vulgaris (Hildenborough).
复制标题
表面酸性氨基酸残基对脱硫弧菌 (Hildenborough) 黄素氧还蛋白氧化还原电位的静电影响。
DOI：
10.1021/bi00010a007
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发表时间：
1995
期刊：
影响因子：
2.9
通讯作者：
Swenson,RP
中科院分区：
文献类型：
--
作者：
Zhou,Z;Swenson,RP
Revised Manuscript Received December 19, 1994® abstract: The flavodoxin from Desulfovibrio vulgaris (Hildenborough) is a member of a family of small, acidic proteins that contain a single noncovalently bound flavin mononucleotide (FMN) cofactor. These proteins function as low-potential one-electrontransferases in bacteria. A distinguishing feature of these flavoproteins is the dramatic decrease in the midpoint potential of the semiquinone/hydroquinone couple of the FMN upon binding to the apoprotein (—172 mV for FMN free in solution versus—443 mV when bound), a perturbation thought to be essential for physiological function. The structural basis of this phenomenon is not yet thoroughly understood. In this study, the contribution of six acidic residues (Asp62, Asp63, Glu66, Asp95, Glu99, and Aspl06) to the perturbation of the redox properties of the cofactor has been investigated. These residues are clustered about the FMN binding site within 13 A of the N (l) atom of the cofactor. Using oligonucleotide-directed mutagenesis, these residues were neutralized in various combinations through the substitution of asparagine for aspartate and glutamine for glutamate. Seventeen mutant flavodoxins were generated in which one to all six acidic residues were systematically neutralized, often in variousspatial configurations. There was no obvious correlation between the midpoint potentials for the oxidized/semiquinone couple and general electrostatic environment, although some differences were noted. However, the midpoint potential for the semiquinone/hydroquinone couple for each of the mutants was less negative than that of the wild type. These increases are strongly correlated with the number of acid to amide substitutions, with an average contribution of about 15 mV per substitution. Collectively, the unfavorable electrostatic environment provided by these acidic residuesaccounts for approximately one-third of the large midpoint potential shift for the semiquinone/hydroquinone couple that typifies the flavodoxinfamily, apparently through the destabilization of the flavin hydroquinone anion.Flavodoxins represent an important family of electrontransferring flavoproteins, containing a single noncovalently bound flavin mononucleotide (FMN) 1 prosthetic group. These acidic proteins have been isolated from a variety of sources, and their molecular masses range from 14 to 18 kDa [for recent reviews, see Mayhew and Tollin (1992) and Ludwig and Luschinsky (1992)]. A distinguishing feature of the flavodoxin family is the very negative reduction potential for the semiquinone/hydroquinone (sq/hq) couple
