InterPro domain: IPR020616

Two different types of thiolase [ 1 , 2 , 3 ] are found both in eukaryotes and in prokaryotes: acetoacetyl-CoA thiolase ( 2.3.1.9 ) and 3-ketoacyl-CoA thiolase ( 2.3.1.16 ). 3-ketoacyl-CoA thiolase (also called thiolase I) has a broad chain-length specificity for its substrates and is involved in degradative pathways such as fatty acid beta-oxidation. Acetoacetyl-CoA thiolase (also called thiolase II) is specific for the thiolysis of acetoacetyl-CoA and involved in biosynthetic pathways such as poly beta-hydroxybutyrate synthesis or steroid biogenesis.

In eukaryotes, there are two forms of 3-ketoacyl-CoA thiolase: one located in the mitochondrion and the other in peroxisomes.

There are two conserved cysteine residues important for thiolase activity. The first located in the N-terminal section of the enzymes is involved in the formation of an acyl-enzyme intermediate; the second located at the C-terminal extremity is the active site base involved in deprotonation in the condensation reaction.

Mammalian nonspecific lipid-transfer protein (nsL-TP) (also known as sterol carrier protein 2) is a protein which seems to exist in two different forms: a 14 Kd protein (SCP-2) and a larger 58 Kd protein (SCP-x). The former is found in the cytoplasm or the mitochondria and is involved in lipid transport; the latter is found in peroxisomes. The C-terminal part of SCP-x is identical to SCP-2 while the N-terminal portion is evolutionary related to thiolases [ 4 ].

1. Similarity between the amino-terminal portion of mammalian 58-kD sterol carrier protein (SCPx) and Escherichia coli acetyl-CoA acyltransferase: evidence for a gene fusion in SCPx. DNA Cell Biol. 10, 695-8
2. Nucleotide sequence of the fadA gene. Primary structure of 3-ketoacyl-coenzyme A thiolase from Escherichia coli and the structural organization of the fadAB operon. J. Biol. Chem. 265, 10424-9
3. Phylogenetic analysis of the thiolase family. Implications for the evolutionary origin of peroxisomes. J. Mol. Evol. 35, 147-55