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PDBsum entry 1sqc

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Isomerase PDB id
1sqc
Jmol
Contents
Protein chain
619 a.a. *
Ligands
LDA
Waters ×38
* Residue conservation analysis
PDB id:
1sqc
Name: Isomerase
Title: Squalene-hopene-cyclase from alicyclobacillus acidocaldarius
Structure: Squalene-hopene cyclase. Chain: a. Engineered: yes
Source: Alicyclobacillus acidocaldarius. Organism_taxid: 405212. Cell_line: jm105. Atcc: 27009. Cellular_location: membrane. Expressed in: escherichia coli k12. Expression_system_taxid: 83333. Expression_system_cell_line: jm105. Other_details: thermostable, acidophilic
Resolution:
2.85Å     R-factor:   0.167     R-free:   0.243
Authors: K.U.Wendt,G.E.Schulz
Key ref:
K.U.Wendt et al. (1997). Structure and function of a squalene cyclase. Science, 277, 1811-1815. PubMed id: 9295270 DOI: 10.1126/science.277.5333.1811
Date:
01-Sep-97     Release date:   17-Dec-97    
PROCHECK
Go to PROCHECK summary
 Headers
 References

Protein chain
Pfam   ArchSchema ?
P33247  (SQHC_ALIAD) -  Squalene--hopene cyclase
Seq:
Struc:
 
Seq:
Struc:
631 a.a.
619 a.a.
Key:    PfamA domain  Secondary structure  CATH domain

 Enzyme reactions 
   Enzyme class 2: E.C.4.2.1.129  - Squalene--hopanol cyclase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]
      Reaction: Hopan-22-ol = squalene + H2O
Hopan-22-ol
= squalene
+ H(2)O
   Enzyme class 3: E.C.5.4.99.17  - Squalene--hopene cyclase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]

      Pathway:
      Reaction: Squalene = hop-2229-ene
Squalene
= hop-22(29)-ene
Note, where more than one E.C. class is given (as above), each may correspond to a different protein domain or, in the case of polyprotein precursors, to a different mature protein.
Molecule diagrams generated from .mol files obtained from the KEGG ftp site
 Gene Ontology (GO) functional annotation 
  GO annot!
  Cellular component     membrane   2 terms 
  Biological process     hopanoid biosynthetic process   1 term 
  Biochemical function     lyase activity     4 terms  

 

 
    reference    
 
 
DOI no: 10.1126/science.277.5333.1811 Science 277:1811-1815 (1997)
PubMed id: 9295270  
 
 
Structure and function of a squalene cyclase.
K.U.Wendt, K.Poralla, G.E.Schulz.
 
  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.
 
  Selected figure(s)  
 
Figure 1.
Fig. 1. The proposed reaction steps in squalene-hopene cyclases involving carbocationic intermediates. The general acid B[1]:H protonates (H) squalene at C3, whereas the general base B[2] deprotonates at C29 of the hopenyl cation. In a side reaction, the cation is hydroxylated^ forming hopan-22-ol.
Figure 5.
Fig. 5. The color-coded surface representations (30) with nonpolar (yellow), positive (blue), and negative (red) areas. (A) View similar to Fig. 2 but rotated around a vertical axis and^ sliced. The cutting plane (checked) opens the large internal cavity with the bound inhibitor LDAO. The nonpolar channel runs to the^ left, opening into a nonpolar plateau. The channel constriction (C) appears closed, but it is mobile enough to be readily opened. At the upper left, hopane (two views) is shown at scale. (B) View similar to Fig. 2 directly onto the 1600 Å2 nonpolar plateau with the channel entrance (E) at its center and two nonpolar side chains pointing to the outside. This is the only large nonpolar region on the surface.
 
  The above figures are reprinted by permission from the AAAs: Science (1997, 277, 1811-1815) copyright 1997.  
  Figures were selected by the author.  

Literature references that cite this PDB file's key reference

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The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time. Where a reference describes a PDB structure, the PDB codes are shown on the right.