L-carnitine CoA-transferase CaiB (IPR023452)

Short name: CoA-Trfase_CaiB

Overlapping homologous superfamilies

Family relationships


CoA-transferases are found in organisms from all kingdoms of life. They catalyse reversible transfer reactions of coenzyme A groups from CoA-thioesters to free acids. There are at least three families of CoA-transferases, which differ in sequence and reaction mechanism:

  • Family I consists of CoA-transferases for 3-oxoacids (EC:, EC:, short-chain fatty acids (EC:, EC: and glutaconate (EC: Most use succinyl-CoA or acetyl-CoA as CoA donors.
  • Family II consists of the homodimeric alpha-subunits of citrate lyase and citramalate lyase (EC:, EC: These enzymes catalyse the transfer of acyl carrier protein (ACP) with a covalently bound CoA derivative, but can accept free CoA thioesters as well.
  • Family III consists of formyl-CoA:oxalate CoA-transferase [PMID: 15213226], succinyl-CoA:(R)-benzylsuccinate CoA-transferase [PMID: 11418570], (E)-cinnamoyl-CoA:(R)-phenyllactate CoA-transferase [PMID: 10849007], and butyrobetainyl-CoA:(R)-carnitine CoA-transferase [PMID: 15823031]. These CoA-transferases occur in prokaryotes and eukaryotes, and catalyse CoA-transfer reactions in a highly substrate- and stereo-specific manner [PMID: 11749953].

CaiB is a family III CoA-transferase that catalyzes the reversible transfer of the CoA moiety from gamma-butyrobetainyl-CoA to L-carnitine to generate L-carnitinyl-CoA and gamma-butyrobetaine [PMID: 11551212]. This enzyme can also catalyse the reversible transfer of the CoA moiety from gamma-butyrobetainyl-CoA or L-carnitinyl-CoA to crotonobetaine to generate crotonobetainyl-CoA. In Escherichia coli, CaiB is one of the genes encoded by the caiTABCDE operon [PMID: 7815937]. The adjacent but divergent fixABCD operon also appears to be necessary for carnintine meatbolism [PMID: 12081978].

CaiB is composed of two identical circular chains that together form an intertwined dimer. Each monomer consists of a large domain, containing a Rossmann fold, and a small domain [PMID: 15823031].

GO terms

Biological Process

GO:0009437 carnitine metabolic process

Molecular Function

GO:0016782 transferase activity, transferring sulfur-containing groups

Cellular Component

No terms assigned in this category.

Contributing signatures

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