Crystal Structures of the Binary and Ternary Complexes of 7-Hydroxysteroid Dehydrogenase from Escherichia coli
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- 作者：Nobutada Tanaka ; Takamasa Nonaka ; Tetsurou Tanabe ; Tadashi Yoshimoto ; Daisuke Tsuru ; and Yukio Mitsui
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：June 18, 1996
- 年：1996
- 卷：35
- 期：24
- 页码：7715 - 7730
- 全文大小：986K
- 年卷期：v.35,no.24(June 18, 1996)
- ISSN：1520-4995
文摘
7
-Hydroxysteroid dehydrogenase (7-HSDH;1 EC1.1.1.159) is an NAD+-dependentoxidoreductase belonging to the short-chain dehydrogenase/reductase(SDR)1 family. It catalyzes thedehydrogenation of a hydroxyl group at position 7 of the steroidskeleton of bile acids. The crystalstructure of the binary (complexed with NAD+) complex of7-HSDH has been solved at 2.3 Å resolutionby the multiple isomorphous replacement method. The structure ofthe ternary complex [the enzymecomplexed with NADH, 7-oxoglycochenodeoxycholic acid (as a reactionproduct), and possibly partiallyglycochenodeoxycholic acid (as a substrate)] has been determined by adifference Fourier method at 1.8Å resolution. The enzyme 7-HSDH is an /
doubly woundprotein having a Rossmann-fold domainfor NAD(H) binding. Upon substrate binding, largeconformation changes occur at the substrate bindingloop (between the F strand and the G helix) and the C-terminalsegment (residues 250-255). Thevariable amino acid sequences of the substrate-binding loop appear tobe responsible for the wide varietyof substrate specificities observed among the enzymes of the SDRfamily. The crystal structure of theternary complex of 7-HSDH, which is the only structure available asthe ternary complex among theenzymes of the SDR family, indicates that the highly conserved Tyr159and Ser146 residues most probablydirectly interact with the hydroxyl group of the substrates althoughthis observation cannot be definitedue to an insufficiently characterized nature of the ternary complex.The strictly conserved Lys163 ishydrogen-bonded to both the 2'- and 3'-hydroxyl groups of thenicotinamide ribose of NAD(H). Wepropose a new catalytic mechanism possibly common to all the enzymesbelonging to the SDR family inwhich a tyrosine residue (Tyr159) acts as a catalytic base and a serineresidue (Ser146) plays a subsidiaryrole of stabilizing substrate binding.
-Hydroxysteroid dehydrogenase (7-HSDH;1 EC1.1.1.159) is an NAD+-dependentoxidoreductase belonging to the short-chain dehydrogenase/reductase(SDR)1 family. It catalyzes thedehydrogenation of a hydroxyl group at position 7 of the steroidskeleton of bile acids. The crystalstructure of the binary (complexed with NAD+) complex of7-HSDH has been solved at 2.3 Å resolutionby the multiple isomorphous replacement method. The structure ofthe ternary complex [the enzymecomplexed with NADH, 7-oxoglycochenodeoxycholic acid (as a reactionproduct), and possibly partiallyglycochenodeoxycholic acid (as a substrate)] has been determined by adifference Fourier method at 1.8Å resolution. The enzyme 7-HSDH is an / doubly woundprotein having a Rossmann-fold domainfor NAD(H) binding. Upon substrate binding, largeconformation changes occur at the substrate bindingloop (between the F strand and the G helix) and the C-terminalsegment (residues 250-255). Thevariable amino acid sequences of the substrate-binding loop appear tobe responsible for the wide varietyof substrate specificities observed among the enzymes of the SDRfamily. The crystal structure of theternary complex of 7-HSDH, which is the only structure available asthe ternary complex among theenzymes of the SDR family, indicates that the highly conserved Tyr159and Ser146 residues most probablydirectly interact with the hydroxyl group of the substrates althoughthis observation cannot be definitedue to an insufficiently characterized nature of the ternary complex.The strictly conserved Lys163 ishydrogen-bonded to both the 2'- and 3'-hydroxyl groups of thenicotinamide ribose of NAD(H). Wepropose a new catalytic mechanism possibly common to all the enzymesbelonging to the SDR family inwhich a tyrosine residue (Tyr159) acts as a catalytic base and a serineresidue (Ser146) plays a subsidiaryrole of stabilizing substrate binding.