InterPro domain: IPR012703

Phosphonates are a class of organophosphorus compounds, characterised by a stable C-P bond, which are found in a variety of biologically produced molecules including antiobiotics, lipids, proteins and polysaccharides [ 1 ]. The functions of these molecules include phosphorus storage, cell communication, host recognition and chemical warfare. 2-Aminoethylphosphonate (AEP), the most common naturally occurring phosphonate, is an important precursor used in the biosynthesis of phosphonolipids, phosphonoproteins, and phosphonoglycans.

This entry represents 2-aminoethylphosphonate-pyruvate transaminase (AEPT) ( 2.6.1.37 ) which catalyses the interconversion of AEP and phosphonoacetaldehyde (P-Ald), coupled with the interconversion of pryuvate and L-alanine. In some bacterial species this is the first step in an AEP degradation pathway which allows them to utilise this compound as a source of carbon, nitrogen and phosphorus. Phosphonoacetaldeyhde hydrolase, often encoded by an adjacent gene, then converts P-Ald to acetaldehyde and phosphate. Species with this pathway generally have an identified phosphonate ABC transporter but do not also have the multisubunit C-P lyase complex as found in Escherichia coli.

The crystal structure of AEPT from Salmonella typhimurium has been studied to 2.2 A resolution [ 2 ]. The protein is a homodimer where each subunit is composed of two domains, large and small. The large domain forms an alpha-beta complex characteristic of the aspartate transaminase family, while the small domain is composed of highly twisted beta strands. The active site contains a pyridoxal 5'-phosphate cofactor and is found at the domain interface, being composed of residues from both subunits.

1. Phosphonates and their degradation by microorganisms. Biochemistry Mosc. 67, 184-95
2. Degradation pathway of the phosphonate ciliatine: crystal structure of 2-aminoethylphosphonate transaminase. Biochemistry 41, 13162-9