The refined three-dimensional structure of 3α,20β-hydroxysteroid dehydrogenase and possible roles of the residues conserved in short-chain dehydrogenases

184

227

Retinoids are chromophores involved in vision, transcriptional regulation, and cellular differentiation. Members of the short chain alcohol dehydrogenase/reductase superfamily catalyze the transformation of retinol to retinal. Here, we describe the identification and properties of three enzymes from a novel subfamily of four retinol dehydrogenases (RDH11-14) that display dualsubstrate specificity, uniquely metabolizing all-trans-and cis-retinols with C 15 pro-R specificity. RDH11-14 could be involved in the first step of all-trans-and 9-cis-retinoic acid production in many tissues. RDH11-14 fill the gap in our understanding of 11-cis-retinal and all-trans-retinal transformations in photoreceptor (RDH12) and retinal pigment epithelial cells (RDH11). The dualsubstrate specificity of RDH11 explains the minor phenotype associated with mutations in 11-cisretinol dehydrogenase (RDH5) causing fundus albipunctatus in humans and engineered mice lacking RDH5. Furthermore, photoreceptor RDH12 could be involved in the production of 11-cis-retinal from 11-cis-retinol during regeneration of the cone visual pigments. These newly identified enzymes add new elements to important retinoid metabolic pathways that have not been explained by previous genetic and biochemical studies.Retinoids are indispensable light-sensitive elements of vision and also serve as essential modulators of cellular differentiation and proliferation in diverse cell types, including those comprising the epithelium and immune system. Retinoids modulate the growth of both normal and malignant cells through their binding to retinoid receptors. All-trans-retinoic acid signals through specific interactions with the nuclear retinoic acid receptors, whereas its isomer, 9-cis-retinoic acid, is a high affinity ligand of retinoic acid receptors and retinoid X receptors. In the retina, light-dependent photoisomerization of 11-cis-retinylidene to the all-transretinylidene moiety of rod and cone photoreceptors is a key reaction that triggers visual * This research was supported by National Institutes of Health Grants EY08061, CA75173, and DK59125, a grant from Research to Prevent Blindness, Inc. (to the Department of Ophthalmology, University of Washington), and by the E. K. Bishop Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. S The on-line version of this article (available at http://www.jbc.org) contains Supplemental Figs. 1 and 2 and Tables 1-3. § These authors contributed equally to this work. § § Recipient of a Research to Prevent Blindness Senior Investigator Award. To whom correspondence should be addressed: Dept. of Ophthalmology, University of Washington, Seattle,; E-mail: palczews@u.washington.edu. Transformations of retinoids occur mostly through enzymatic or photochemical reactions, although they readily isomerize non-enzymatically to thermodynamic equilibriu...

Section: Dual-substrate Specificity Dual Responsibility; Mechanisticsupporting

confidence: 76%

Dual-substrate Specificity Short Chain Retinol Dehydrogenases from the Vertebrate Retina

Haeseleer¹,

Jang²,

Imanishi³

et al. 2002

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227

“…All structures of homotetrameric SDRs determined so far exhibit two main subunit interfaces arranged about two non-crystallographic 2-fold axes which are perpendicular to each other and referred to as P and Q (Fig. 4A) (10,27). The P-axis interface is mainly formed by the ␣G helices and by side chain-to-main chain interactions between the ␤G strands of two neighboring subunits.…”

Section: Resultsmentioning

confidence: 99%

The Crystal Structure of 3α-Hydroxysteroid Dehydrogenase/Carbonyl Reductase from Comamonas testosteroni Shows a Novel Oligomerization Pattern within the Short Chain Dehydrogenase/Reductase Family

Grimm¹,

Maser²,

Möbus³

et al. 2000

The crystal structure of 3␣-hydroxysteroid dehydrogenase/carbonyl reductase from Comamonas testosteroni (3␣-HSDH) as well as the structure of its binary complex with NAD ؉ have been solved at 1.68-Å and 1.95-Å resolution, respectively. The enzyme is a member of the short chain dehydrogenase/reductase (SDR) family. Accordingly, the active center and the conformation of the bound nucleotide cofactor closely resemble those of other SDRs. The crystal structure reveals one homodimer per asymmetric unit representing the physiologically active unity. Dimerization takes place via an interface essentially built-up by helix ␣G and strand ␤G of each subunit. So far this type of intermolecular contact has exclusively been observed in homotetrameric SDRs but never in the structure of a homodimeric SDR. The formation of a tetramer is blocked in 3␣-HSDH by the presence of a predominantly ␣-helical subdomain which is missing in all other SDRs of known structure.

“…This hydrogen bond network is presumed to lower the pK a of the Tyr hydroxyl group, which functions as the catalytic base. Ser has been suggested to either stabilize the substrate (13,14) or to interact with Tyr (15). Additionally, an Asn residue has been proposed to stabilize the position of the Lys residue, thereby forming a proton relay system involving water (16).…”

mentioning

confidence: 99%

Removal of Substrate Inhibition and Increase in Maximal Velocity in the Short Chain Dehydrogenase/Reductase Salutaridine Reductase Involved in Morphine Biosynthesis

Ziegler

Brandt

Geißler

et al. 2009

Salutaridine reductase (SalR, EC 1.1.1.248) catalyzes the stereospecific reduction of salutaridine to 7(S)-salutaridinol in the biosynthesis of morphine. It belongs to a new, plant-specific class of short-chain dehydrogenases, which are characterized by their monomeric nature and increased length compared with related enzymes. Homology modeling and substrate docking suggested that additional amino acids form a novel ␣-helical element, which is involved in substrate binding. Site-directed mutagenesis and subsequent studies on enzyme kinetics revealed the importance of three residues in this element for substrate binding. Further replacement of eight additional residues led to the characterization of the entire substrate binding pocket. In addition, a specific role in salutaridine binding by either hydrogen bond formation or hydrophobic interactions was assigned to each amino acid. Substrate docking also revealed an alternative mode for salutaridine binding, which could explain the strong substrate inhibition of SalR. An alternate arrangement of salutaridine in the enzyme was corroborated by the effect of various amino acid substitutions on substrate inhibition. In most cases, the complete removal of substrate inhibition was accompanied by a substantial loss in enzyme activity. However, some mutations greatly reduced substrate inhibition while maintaining or even increasing the maximal velocity. Based on these results, a double mutant of SalR was created that exhibited the complete absence of substrate inhibition and higher activity compared with wild-type SalR.