2sqc
From Proteopedia
(New page: 200px<br /><applet load="2sqc" size="450" color="white" frame="true" align="right" spinBox="true" caption="2sqc, resolution 2.0Å" /> '''SQUALENE-HOPENE CYCLA...) |
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| - | [[Image:2sqc.jpg|left|200px]]<br /><applet load="2sqc" size=" | + | [[Image:2sqc.jpg|left|200px]]<br /><applet load="2sqc" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="2sqc, resolution 2.0Å" /> | caption="2sqc, resolution 2.0Å" /> | ||
'''SQUALENE-HOPENE CYCLASE FROM ALICYCLOBACILLUS ACIDOCALDARIUS'''<br /> | '''SQUALENE-HOPENE CYCLASE FROM ALICYCLOBACILLUS ACIDOCALDARIUS'''<br /> | ||
==Overview== | ==Overview== | ||
| - | Squalene cyclases catalyze a cationic cyclization cascade, which is | + | Squalene cyclases catalyze a cationic cyclization cascade, which is homologous to a key step in cholesterol biosynthesis. The structure of the enzyme from Alicyclobacillus acidocaldarius has been determined in a new crystal form at 2.0 A resolution (1 A=0.1 nm) and refined to an R-factor of 15.3 % (Rfree=18.7 %). The structure indicates how the initial protonation and the final deprotonation of squalene occur and how the transient carbocations are stabilized. The pathways of the flexible educt squalene from the membrane interior to the active center cavity and of the rigid fused-ring product hopene in the reverse direction are discussed. The enzyme contains eight so-called QW-sequence repeats that fortify the alpha/alpha-barrels by an intricate interaction network. They are unique to the known triterpene cyclases and are presumed to shield these enzymes against the released enthalpy of the highly exergonic catalyzed reaction. The enzyme is a monotopic membrane protein, the membrane-binding interactions of which are described and compared with those of two prostaglandin-H2 synthase isoenzymes, the only other structurally characterized proteins of this type. In the crystals the membrane-binding regions face each other, suggesting a micelle-type detergent structure between them. |
==About this Structure== | ==About this Structure== | ||
| - | 2SQC is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Alicyclobacillus_acidocaldarius Alicyclobacillus acidocaldarius] with C8E as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http:// | + | 2SQC is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Alicyclobacillus_acidocaldarius Alicyclobacillus acidocaldarius] with <scene name='pdbligand=C8E:'>C8E</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2SQC OCA]. |
==Reference== | ==Reference== | ||
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[[Category: Alicyclobacillus acidocaldarius]] | [[Category: Alicyclobacillus acidocaldarius]] | ||
[[Category: Single protein]] | [[Category: Single protein]] | ||
| - | [[Category: Schulz, G | + | [[Category: Schulz, G E.]] |
| - | [[Category: Wendt, K | + | [[Category: Wendt, K U.]] |
[[Category: C8E]] | [[Category: C8E]] | ||
[[Category: cholesterol biosynthesis]] | [[Category: cholesterol biosynthesis]] | ||
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[[Category: triterpene cyclase]] | [[Category: triterpene cyclase]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 18:49:27 2008'' |
Revision as of 16:49, 21 February 2008
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SQUALENE-HOPENE CYCLASE FROM ALICYCLOBACILLUS ACIDOCALDARIUS
Overview
Squalene cyclases catalyze a cationic cyclization cascade, which is homologous to a key step in cholesterol biosynthesis. The structure of the enzyme from Alicyclobacillus acidocaldarius has been determined in a new crystal form at 2.0 A resolution (1 A=0.1 nm) and refined to an R-factor of 15.3 % (Rfree=18.7 %). The structure indicates how the initial protonation and the final deprotonation of squalene occur and how the transient carbocations are stabilized. The pathways of the flexible educt squalene from the membrane interior to the active center cavity and of the rigid fused-ring product hopene in the reverse direction are discussed. The enzyme contains eight so-called QW-sequence repeats that fortify the alpha/alpha-barrels by an intricate interaction network. They are unique to the known triterpene cyclases and are presumed to shield these enzymes against the released enthalpy of the highly exergonic catalyzed reaction. The enzyme is a monotopic membrane protein, the membrane-binding interactions of which are described and compared with those of two prostaglandin-H2 synthase isoenzymes, the only other structurally characterized proteins of this type. In the crystals the membrane-binding regions face each other, suggesting a micelle-type detergent structure between them.
About this Structure
2SQC is a Single protein structure of sequence from Alicyclobacillus acidocaldarius with as ligand. Full crystallographic information is available from OCA.
Reference
The structure of the membrane protein squalene-hopene cyclase at 2.0 A resolution., Wendt KU, Lenhart A, Schulz GE, J Mol Biol. 1999 Feb 12;286(1):175-87. PMID:9931258
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