3sqc
From Proteopedia
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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 Alicyclobacillus acidocaldarius. 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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