1SQC

SQUALENE-HOPENE-CYCLASE FROM ALICYCLOBACILLUS ACIDOCALDARIUS

• PDB DOI: https://doi.org/10.2210/pdb1SQC/pdb

• Classification: ISOMERASE
• Organism(s): Alicyclobacillus acidocaldarius
• Expression System: Escherichia coli K-12
• Mutation(s): No 


• Deposited: 1997-09-01 Released: 1997-12-17 
• Deposition Author(s): Wendt, K.U., Schulz, G.E.

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 2.85 Å
• R-Value Free: 0.243 
• R-Value Work: 0.167 
• R-Value Observed: 0.167 

Literature

Structure and function of a squalene cyclase.

Wendt, K.U., Poralla, K., Schulz, G.E.

(1997) Science 277: 1811-1815

• PubMed: 9295270 
• DOI: https://doi.org/10.1126/science.277.5333.1811
• Primary Citation of Related Structures:  
  1SQC


• PubMed Abstract: 
  

  The crystal structure of squalene-hopene cyclase from Alicyclobacillus acidocaldarius was determined at 2.9 angstrom resolution. The mechanism and sequence of this cyclase are closely related to those of 2,3-oxidosqualene cyclases that catalyze the cyclization step in cholesterol biosynthesis. The structure reveals a membrane protein with membrane-binding characteristics similar to those of prostaglandin-H2 synthase, the only other reported protein of this type. The active site of the enzyme is located in a large central cavity that is of suitable size to bind squalene in its required conformation and that is lined by aromatic residues. The structure supports a mechanism in which the acid starting the reaction by protonating a carbon-carbon double bond is an aspartate that is coupled to a histidine. Numerous surface alpha helices are connected by characteristic QW-motifs (Q is glutamine and W is tryptophan) that tighten the protein structure, possibly for absorbing the reaction energy without structural damage.

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Organizational Affiliation: 

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

Biological Assembly 1  

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Monomer - A1 

Biological assembly 1 assigned by authors.

Macromolecule Content

• Total Structure Weight: 71.88 kDa 
• Atom Count: 5,017 
• Modelled Residue Count: 619 
• Deposited Residue Count: 631 
• Unique protein chains: 1

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
SQUALENE-HOPENE CYCLASE	A	631	Alicyclobacillus acidocaldarius	Mutation(s): 0  EC: 5.4.99 (PDB Primary Data), 5.4.99.17 (UniProt), 4.2.1.129 (UniProt)
UniProt
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

Small Molecules

Ligands 1 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
LDA	B [auth A]	LAURYL DIMETHYLAMINE-N-OXIDE C14 H31 N O SYELZBGXAIXKHU-UHFFFAOYSA-N

Binding Affinity Annotations
ID	Source	Binding Affinity
LDA	PDBBind:  1SQC	Ki: 140 (nM) from 1 assay(s)

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 2.85 Å
• R-Value Free: 0.243 
• R-Value Work: 0.167 
• R-Value Observed: 0.167 
• Space Group: P 3 2 1

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 140.7	α = 90
b = 140.7	β = 90
c = 81.9	γ = 120

Software Package:

Software Name	Purpose
X-PLOR	model building
X-PLOR	refinement
XDS	data reduction
XSCALE	data scaling
CCP4	data scaling
X-PLOR	phasing

Structure Validation

Entry History 

Deposition Data

• Released Date: 1997-12-17 
Deposition Author(s): Wendt, K.U., Schulz, G.E.

Revision History  

• Version 1.0: 1997-12-17
  Type: Initial release
  
• Version 1.1: 2008-03-24
  Changes: Version format compliance
• Version 1.2: 2011-07-13
  Changes: Version format compliance
• Version 1.3: 2024-02-14
  Changes: Data collection, Database references, Derived calculations, Other