Experimental Data Snapshot

  • Resolution: 2.00 Å
  • R-Value Free: 0.187 
  • R-Value Work: 0.153 

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This is version 1.4 of the entry. See complete history


The structure of the membrane protein squalene-hopene cyclase at 2.0 A resolution.

Wendt, K.U.Lenhart, A.Schulz, G.E.

(1999) J Mol Biol 286: 175-187

  • DOI: https://doi.org/10.1006/jmbi.1998.2470
  • Primary Citation of Related Structures:  
    2SQC, 3SQC

  • PubMed Abstract: 

    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.

  • Organizational Affiliation

    Institut für Organische Chemie und Biochemie, Albertstr. 21, Freiburg im Breisgau, D-79104, Germany.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
631Alicyclobacillus acidocaldariusMutation(s): 2 
EC: 5.4.99
Membrane Entity: Yes 
Find proteins for P33247 (Alicyclobacillus acidocaldarius subsp. acidocaldarius (strain ATCC 27009 / DSM 446 / BCRC 14685 / JCM 5260 / KCTC 1825 / NBRC 15652 / NCIMB 11725 / NRRL B-14509 / 104-IA))
Explore P33247 
Go to UniProtKB:  P33247
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP33247
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.00 Å
  • R-Value Free: 0.187 
  • R-Value Work: 0.153 
  • Space Group: P 43 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 118.82α = 90
b = 118.82β = 90
c = 276.2γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
CCP4data scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1999-04-27
    Type: Initial release
  • Version 1.1: 2008-03-03
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2021-11-03
    Changes: Database references, Derived calculations
  • Version 1.4: 2023-08-09
    Changes: Refinement description