View source for 3sqc

[[Image:3sqc.jpg|left|200px]]

 {{Structure
|PDB= 3sqc |SIZE=350|CAPTION= <scene name='initialview01'>3sqc</scene>, resolution 2.8&Aring;
|SITE= 
|LIGAND= 
|ACTIVITY= 
|GENE= 
|DOMAIN=
|RELATEDENTRY=
|RESOURCES=<span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=3sqc FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=3sqc OCA], [http://www.ebi.ac.uk/pdbsum/3sqc PDBsum], [http://www.rcsb.org/pdb/explore.do?structureId=3sqc RCSB]</span>
}}

'''SQUALENE-HOPENE CYCLASE'''


==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==
3SQC is a [[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==
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:[http://www.ncbi.nlm.nih.gov/pubmed/9931258 9931258]
[[Category: Alicyclobacillus acidocaldarius]]
[[Category: Single protein]]
[[Category: Schulz, G E.]]
[[Category: Wendt, K U.]]
[[Category: cholesterol biosynthesis]]
[[Category: isomerase]]
[[Category: monotopic membrane protein]]
[[Category: qw-sequence repeat]]
[[Category: triterpene cyclase]]

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