Ketosteroid Isomerase
From Proteopedia
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==Ketosteroid Isomerase== | ==Ketosteroid Isomerase== | ||
==Introduction== | ==Introduction== | ||
| - | <applet load='1ISK' size=' | + | <applet load='1ISK' size='400' frame='true' align='right' caption='Ketosteroid Isomerase (KSI; PDB 1ISK)' scene='User:Laura_M._Haynes/Sandbox_1/Ksi/4' /> |
Ketosteroid isomerase (KSI, EC#5.3.3.1) is an enzyme that catalyzes the isomerization of 3-oxo-Δ<sup>5</sup> ketosteroids to their hormonally active Δ<sup>4</sup>-conjugated isomers, as illustrated below.<ref name="Pollack">PMID:15381400</ref>, <ref name="Talalay">PMID:7358699</ref> | Ketosteroid isomerase (KSI, EC#5.3.3.1) is an enzyme that catalyzes the isomerization of 3-oxo-Δ<sup>5</sup> ketosteroids to their hormonally active Δ<sup>4</sup>-conjugated isomers, as illustrated below.<ref name="Pollack">PMID:15381400</ref>, <ref name="Talalay">PMID:7358699</ref> | ||
[[Image:Reaction.jpg]] | [[Image:Reaction.jpg]] | ||
| - | This reaction is essential in the biosynthesis of steroids in mammals where KSI is a membrane-bound complex.<ref name="Ha">PMID:11751047</ref> In bacteria, however, KSI exists as a soluble protein is involves in catabolism of steroids.<ref name="Ha" /> It was first isolated in and has been extensively studied in ''Commamonas tetosteroni'' (TI), a bacteria that is capable of It is one of the most efficient known enzymes with an essentially diffusion limited rate of catalysis. | + | This reaction is essential in the biosynthesis of steroids in mammals where KSI is a membrane-bound complex.<ref name="Ha">PMID:11751047</ref> In bacteria, however, KSI exists as a soluble protein is involves in catabolism of steroids.<ref name="Ha" /> It was first isolated in and has been extensively studied in ''Commamonas tetosteroni'' (TI), a bacteria that is capable of It is one of the most efficient known enzymes with an essentially diffusion limited rate of catalysis.<ref name="Talalay" /> |
An NMR solution phase structure of KSI was solved in 1997 by Wu ''et al.''<ref name="Wu">PMID:9103200 </ref> allowing greater insight into the mechanism of this intriguing enzyme. | An NMR solution phase structure of KSI was solved in 1997 by Wu ''et al.''<ref name="Wu">PMID:9103200 </ref> allowing greater insight into the mechanism of this intriguing enzyme. | ||
==Structure== | ==Structure== | ||
| - | Ketosteroid isomerase exits as a 28 kDa homodimeric protein, in which the two dimers related to each other via hydrophobic and electrostatic interactions.<ref name="Wu" /> Each dimer consists of a curved <scene name='User:Laura_M._Haynes/Sandbox_1/Beta_sheets/1'>beta-sheets</scene> and three | + | Ketosteroid isomerase exits as a 28 kDa homodimeric protein, in which the two dimers related to each other via hydrophobic and electrostatic interactions.<ref name="Wu" /> Each dimer consists of a curved <scene name='User:Laura_M._Haynes/Sandbox_1/Beta_sheets/1'>beta-sheets</scene> and three <scene name='User:Laura_M._Haynes/Sandbox_1/Alpha_helices/1'>alpha-helices</scene>. These secondary structures define a conical closed barrel geometry, with one open and one closed end, and create a deep pocket in which the active site resides.<ref name="Ha" />,<ref name="Cho">PMID:9622484 </ref> This unique geometry is shared by several other proteins (scytalone dehydratase, nuclear transport factor 2, and naphthalene 1,2-dioxygenase), however, these molecules do not share functional or sequence homology. It is speculated that this unique protein structure may enable better binding of hydrophobic substrates such as steroids.<ref name="Ha" /> |
==Enzyme Mechanism== | ==Enzyme Mechanism== | ||
Revision as of 17:43, 3 April 2010
Contents |
Ketosteroid Isomerase
Introduction
|
Ketosteroid isomerase (KSI, EC#5.3.3.1) is an enzyme that catalyzes the isomerization of 3-oxo-Δ5 ketosteroids to their hormonally active Δ4-conjugated isomers, as illustrated below.[1], [2]
This reaction is essential in the biosynthesis of steroids in mammals where KSI is a membrane-bound complex.[3] In bacteria, however, KSI exists as a soluble protein is involves in catabolism of steroids.[3] It was first isolated in and has been extensively studied in Commamonas tetosteroni (TI), a bacteria that is capable of It is one of the most efficient known enzymes with an essentially diffusion limited rate of catalysis.[2]
An NMR solution phase structure of KSI was solved in 1997 by Wu et al.[4] allowing greater insight into the mechanism of this intriguing enzyme.
Structure
Ketosteroid isomerase exits as a 28 kDa homodimeric protein, in which the two dimers related to each other via hydrophobic and electrostatic interactions.[4] Each dimer consists of a curved and three . These secondary structures define a conical closed barrel geometry, with one open and one closed end, and create a deep pocket in which the active site resides.[3],[5] This unique geometry is shared by several other proteins (scytalone dehydratase, nuclear transport factor 2, and naphthalene 1,2-dioxygenase), however, these molecules do not share functional or sequence homology. It is speculated that this unique protein structure may enable better binding of hydrophobic substrates such as steroids.[3]
Enzyme Mechanism
The hydrophobic active site of ketosteroid isomerase contains an aspartate residue at position 99 and a tyrosine residue at position 14 (according to the numbering for the Commamonas tetosteroni protein, which will be used throughout) that are capable of binding the 3-position carbonyl of the steroid. Additionally, the active site contains an aspartate residue at position 38 that is participates in the catalytic activity of KSI.[1] The general mechanism of the proposed reaction involves the
Related Proteins
Available Structures
References
- ↑ 1.0 1.1 Pollack RM. Enzymatic mechanisms for catalysis of enolization: ketosteroid isomerase. Bioorg Chem. 2004 Oct;32(5):341-53. PMID:15381400 doi:10.1016/j.bioorg.2004.06.005
- ↑ 2.0 2.1 Smith SB, Richards JW, Benisek WF. The purification and characterization of delta 5-3-ketosteroid isomerase from Pseudomonas putida, a cysteine-containing isomerase. J Biol Chem. 1980 Apr 10;255(7):2678-84. PMID:7358699
- ↑ 3.0 3.1 3.2 3.3 Ha NC, Choi G, Choi KY, Oh BH. Structure and enzymology of Delta5-3-ketosteroid isomerase. Curr Opin Struct Biol. 2001 Dec;11(6):674-8. PMID:11751047
- ↑ 4.0 4.1 Wu ZR, Ebrahimian S, Zawrotny ME, Thornburg LD, Perez-Alvarado GC, Brothers P, Pollack RM, Summers MF. Solution structure of 3-oxo-delta5-steroid isomerase. Science. 1997 Apr 18;276(5311):415-8. PMID:9103200
- ↑ Cho HS, Choi G, Choi KY, Oh BH. Crystal structure and enzyme mechanism of Delta 5-3-ketosteroid isomerase from Pseudomonas testosteroni. Biochemistry. 1998 Jun 9;37(23):8325-30. PMID:9622484 doi:10.1021/bi9801614
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