Domain

Squalene cyclase, N-terminal (IPR032697)

Short name: SQ_cyclase_N

Overlapping homologous superfamilies

Domain relationships

None.

Description

This entry represents the N-terminal domain of squalene cyclases [PMID: 9931258, PMID: 12747780].

Several enzymes catalyse mechanistically related reactions which involve the highly complex cyclic rearrangement of squalene or its 2,3 oxide. Squalene cyclase (SQCY) and 2,3-oxidosqualene cyclase (OSQCY) are integral membrane proteins that catalyze a cationic cyclization cascade converting linear triterpenes to fused ring compounds [PMID: 11027983, PMID: 9295270]. Lanosterol synthase (EC:5.4.99.7) (oxidosqualene--lanosterol cyclase) catalyses the cyclization of (S)-2,3-epoxysqualene to lanosterol, the initial precursor of cholesterol, steroid hormones and vitamin D in vertebrates and of ergosterol in fungi (gene ERG7). Cycloartenol synthase (EC:5.4.99.8) (2,3-epoxysqualene--cycloartenol cyclase), is a plant enzyme that catalyzes the cyclization of (S)-2,3-epoxysqualene to cycloartenol [PMID: 9519404], and hopene synthase (EC:5.4.99) (squalene--hopene cyclase), is a bacterial enzyme that catalyzes the cyclization of squalene into hopene or diplopterol, a key step in hopanoid (triterpenoid) metabolism [PMID: 9931258, PMID: 2253626]. These enzymes are evolutionary related [PMID: 7505443] proteins of about 70 to 85 kDa and have an alpha 6 - alpha 6 barrel fold. Deletion of a single glycine residue of Alicyclobacillus acidocaldarius SQCY alters its substrate specificity into that of eukaryotic OSQCY [PMID: 15593147]. Both enzymes have a second minor domain, which forms an alpha-alpha barrel that is inserted into the major domain.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
Pfam