Ishikita Hiroshi
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
Biochemistry. 2008 Apr 15;47(15):4394-402. doi: 10.1021/bi702151k. Epub 2008 Mar 21.
The redox potential of the flavin mononucleotide (FMN) hydroquinones for one-electron reduction in the Desulfovibrio vulgaris ( D. vulgaris) flavodoxin ( E sq/hq for FMNH (*)/FMNH (-)) was calculated using the crystal structure of the relevant hydroquinone form and compared to the results of the Clostridium beijerinckii ( C. beijerinckii) flavodoxin. In D. vulgaris and C. beijerinckii flavodoxins, the protein side chain causes significant downshifts of 170 and 240 mV in E sq/hq, respectively. In the C. beijerinckii flavodoxin, the E sq/hq downshift because of the protein side chain is essentially compensated by the counter influence of the protein backbone ( E sq/hq upshift of 260 mV). However, in the D. vulgaris flavodoxin, the corresponding protein backbone influence on E sq/hq is significantly small, i.e., less than half of that in the C. beijerinckii flavodoxin. In particular, there is a significant difference in the influence of the protein backbone of the so-called 60s loop region between the two flavodoxins. The E sq/hq difference can be best explained by the lower compensation of the side chain influence by the backbone influence in the D. vulgaris flavodoxin than in the C. beijerinckii flavodoxin.
利用相关对苯二酚形式的晶体结构，计算了普通脱硫弧菌（D. vulgaris）黄素氧还蛋白中黄素单核苷酸（FMN）对苯二酚单电子还原的氧化还原电位（FMNH(*)/FMNH(-)的E sq/hq），并与拜氏梭菌（C. beijerinckii）黄素氧还蛋白的结果进行了比较。在普通脱硫弧菌和拜氏梭菌黄素氧还蛋白中，蛋白质侧链分别导致E sq/hq显著下移170和240 mV。在拜氏梭菌黄素氧还蛋白中，由于蛋白质侧链导致的E sq/hq下移基本上被蛋白质主链的反作用所补偿（E sq/hq上移260 mV）。然而，在普通脱硫弧菌黄素氧还蛋白中，相应的蛋白质主链对E sq/hq的影响显著较小，即不到拜氏梭菌黄素氧还蛋白的一半。特别是，两种黄素氧还蛋白之间所谓的60s环区域的蛋白质主链影响存在显著差异。E sq/hq的差异可以通过普通脱硫弧菌黄素氧还蛋白中主链影响对侧链影响的补偿低于拜氏梭菌黄素氧还蛋白来最好地解释。
