3sqc: Difference between revisions

Revision as of 20:11, 21 February 2008

SQUALENE-HOPENE CYCLASE

OverviewOverview

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 StructureAbout this Structure

3SQC is a Single protein structure of sequence from Alicyclobacillus acidocaldarius. Full crystallographic information is available from OCA.

ReferenceReference

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

Page seeded by OCA on Thu Feb 21 19:11:23 2008

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OCA

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-[[Image:3sqc.jpg|left|200px]]<br /><applet load="3sqc" size="450" color="white" frame="true" align="right" spinBox="true"
+[[Image:3sqc.jpg|left|200px]]<br /><applet load="3sqc" size="350" color="white" frame="true" align="right" spinBox="true"
 caption="3sqc, resolution 2.8&Aring;" />
 '''SQUALENE-HOPENE CYCLASE'''<br />
 ==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.
+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==
-SQC is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Alicyclobacillus_acidocaldarius Alicyclobacillus acidocaldarius]. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=3SQC OCA].
+SQC is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Alicyclobacillus_acidocaldarius Alicyclobacillus acidocaldarius]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3SQC OCA].
 ==Reference==
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 [[Category: Alicyclobacillus acidocaldarius]]
 [[Category: Single protein]]
-[[Category: Schulz, G.E.]]
+[[Category: Schulz, G E.]]
-[[Category: Wendt, K.U.]]
+[[Category: Wendt, K U.]]
 [[Category: cholesterol biosynthesis]]
 [[Category: isomerase]]
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 [[Category: triterpene cyclase]]
-''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Tue Nov 20 19:59:00 2007''
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 19:11:23 2008''