Trans-Isoprenyl Diphosphate Synthases, head-to-head (IPR033904)

Short name: Trans_IPPS_HH

Overlapping homologous superfamilies

Domain relationships



This entry represents a domain found in Trans-Isoprenyl Diphosphate Synthases.

Trans-Isoprenyl Diphosphate Synthases (Trans_IPPS) catalyze a head-to-head (HH) (1'-1) condensation reaction [PMID: 11111076]. This entry includes squalene and phytoene synthases which catalyze the 1'-1 condensation of two 15-carbon (farnesyl) and 20-carbon (geranylgeranyl) isoprenyl diphosphates, respectively [PMID: 8003978,PMID: 11111077,PMID: 10542413,PMID: 9667899],. The catalytic site consists of a large central cavity formed by mostly antiparallel alpha helices with two aspartate-rich regions (DXXXD) located on opposite walls [PMID: 9030588]. These residues mediate binding of prenyl phosphates [PMID: 12135472]. A two-step reaction has been proposed for squalene synthase (farnesyl-diphosphate farnesyltransferase) in which, two molecules of FPP react to form a stable cyclopropylcarbinyl diphosphate intermediate, and then the intermediate undergoes heterolysis, isomerization, and reduction with NADPH to form squalene, a precursor of cholestrol. The carotenoid biosynthesis enzyme, phytoene synthase (CrtB), catalyzes the condensation reaction of two molecules of geranylgeranyl diphosphate to produce phytoene, a precursor of beta-carotene [PMID: 11092953]. These enzymes produce the triterpene and tetraterpene precursors for many diverse sterol and carotenoid end products and are widely distributed among eukareya, bacteria, and archaea [PMID: 9343362].

GO terms

Biological Process

GO:0006696 ergosterol biosynthetic process

Molecular Function

GO:0004310 farnesyl-diphosphate farnesyltransferase activity
GO:0051996 squalene synthase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

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