InterPro domain: IPR012693

The ATP-Binding Cassette (ABC) superfamily forms one of the largest of all protein families with a diversity of physiological functions [ 1 ]. Several studies have shown that there is a correlation between the functional characterisation and the phylogenetic classification of the ABC cassette [ 2 , 2 ]. More than 50 subfamilies have been described based on a phylogenetic and functional classification [ 3 , 3 , 4 ].

Members of this protein family are the ABC transporters of phosphonates. Phosphonates are a class of phosphorus-containing organic compound with a stable direct C-P bond rather than a C-O-P linkage. Phosphonates are widespread among naturally occurring compounds in all kingdoms of wildlife, but only prokaryotic microorganisms are able to cleave this bond. Certain bacteria such as E. coli can use alkylphosphonates as a phosphorus source. A number of bacterial species have operons, typically about 14 genes in size, with genes for ATP-dependent transport of phosphonates, degradation, and regulation of the expression of the system [ 4 , 5 , 6 , 7 , 8 ].

This entry also includes transporters of phosphite (an organophosphorous compound with the formula P(OR) ₃ ) and hypophosphite (H ₂ PO ^- ₂ ), including the phosphite import ATP-binding protein PxtA and hypophosphite import ATP-binding protein HtxD, both from Pseudomonas stutzeri [ 9 ].

1. Getting in or out: early segregation between importers and exporters in the evolution of ATP-binding cassette (ABC) transporters. J. Mol. Evol. 48, 22-41
2. The ABC of ABCS: a phylogenetic and functional classification of ABC systems in living organisms. Res. Microbiol. 152, 211-29
3. ABC transporters: physiology, structure and mechanism--an overview. Res. Microbiol. 152, 205-10
4. Genes for phosphonate biodegradation in Escherichia coli. SAAS Bull. Biochem. Biotechnol. 5, 1-6
5. Phosphonates and their degradation by microorganisms. Biochemistry Mosc. 67, 184-95
6. A phosphate transport system is required for symbiotic nitrogen fixation by Rhizobium meliloti. J. Bacteriol. 178, 4540-7
7. Evidence for a fourteen-gene, phnC to phnP locus for phosphonate metabolism in Escherichia coli. Gene 129, 27-32
8. Involvement of the Escherichia coli phn (psiD) gene cluster in assimilation of phosphorus in the form of phosphonates, phosphite, Pi esters, and Pi. J. Bacteriol. 173, 587-600
9. Molecular genetic analysis of phosphite and hypophosphite oxidation by Pseudomonas stutzeri WM88. J. Bacteriol. 180, 5547-58