Squalene-hopene cyclase
| Squalene-hopene cyclase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
The crystallographic structure of the squalene-hopene cyclase dimer, with the membrane position indicated in blue, the two monomers in green and pink, and a substrate mimetic in the central cavity in yellow. | |||||||||
| Identifiers | |||||||||
| EC no. | 5.4.99.17 | ||||||||
| CAS no. | 76600-69-6 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
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Squalene-hopene cyclase (SHC) (EC 5.4.99.17) or hopan-22-ol hydro-lyase is an enzyme in the terpene cyclase/mutase family. It catalyzes the interconversion of squalene into a pentacyclic triterpenes, hopene and hopanol. This enzyme catalyses the following chemical reactions.
- squalene hop-22(29)-ene
- squalene + H2O hopan-22-ol
SHC is important because its products, hopanoids, are very much like sterols in eukaryotes in that they condense lipid membranes and reduce permeability. In fact, SHC and sterol-producing enzymes (oxidosqualene cyclase) are evolutionarily related to each other. Hopanoids are inferred to provide stability in the face of high temperatures and extreme acidity due to the rigid ring structure. Indeed, up-regulation of SHC occurs in certain bacteria in the presence of hot or acidic environments. SHC is found mostly in bacteria, but some eukaryotes, such as fungi and land plants, are also known to possess the enzyme.