Reaction: 2 S-adenosyl-L-methionine + N-acetyl-demethylphosphinothricin + reduced acceptor = S-adenosyl-L-homocysteine + 5'-deoxyadenosine + L-methionine + N-acetyl-phosphinothricin + oxidized acceptor
Glossary: N-acetyl-demethylphosphinothricin = (2S)-2-acetamido-4-phosphinatobutanoate
Other name(s): phpK (gene name); bcpD (gene name); P-methylase
Systematic name: S-adenosyl-L-methionine:N-acetyl-demethylphosphinothricin P-methyltransferase
Comments: The enzyme was originally characterized from bacteria that produce the tripeptides bialaphos and phosalacine, which inhibit plant and bacterial glutamine synthetases. It is a radical S-adenosyl-L-methionine (SAM) enzyme that contains a [4Fe-4S] center and a methylcob(III)alamin cofactor. According to the proposed mechanism, the reduced iron-sulfur center donates an electron to SAM, resulting in homolytic cleavage of the carbon-sulfur bond to form a 5'-deoxyadenosyl radical that abstracts the hydrogen atom from the P-H bond of the substrate, forming a phosphinate-centered radical. This radical reacts with methylcob(III)alamin to produce the methylated product and cob(II)alamin, which is reduced by an unknown donor to cob(I)alamin. A potential route for restoring the latter back to methylcob(III)alamin is a nucleophilic attack on a second SAM molecule. The enzyme acts in vivo on N-acetyl-demethylphosphinothricin-L-alanyl-L-alanine or N-acetyl-demethylphosphinothricin-L-alanyl-L-leucine, the intermediates in the biosynthesis of bialaphos and phosalacine, respectively. This transformation produces the only example of a carbon-phosphorus-carbon linkage known to occur in nature.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Kamigiri, K., Hidaka, T., Imai, S., Murakami, T. and Seto, H. Studies on the biosynthesis of bialaphos (SF-1293) 12. C-P bond formation mechanism of bialaphos: discovery of a P-methylation enzyme. J. Antibiot. (Tokyo) 45 (1992) 781-787. [PMID: 1624380]
2. Hidaka, T., Hidaka, M., Kuzuyama, T. and Seto, H. Sequence of a P-methyltransferase-encoding gene isolated from a bialaphos-producing Streptomyces hygroscopicus. Gene 158 (1995) 149-150. [PMID: 7789803]
3. Werner, W.J., Allen, K.D., Hu, K., Helms, G.L., Chen, B.S. and Wang, S.C. In vitro phosphinate methylation by PhpK from Kitasatospora phosalacinea. Biochemistry 50 (2011) 8986-8988. [PMID: 21950770]
4. Allen, K.D. and Wang, S.C. Spectroscopic characterization and mechanistic investigation of P-methyl transfer by a radical SAM enzyme from the marine bacterium Shewanella denitrificans OS217. Biochim. Biophys. Acta 1844 (2014) 2135-2144. [PMID: 25224746]
5. Hu, K., Werner, W.J., Allen, K.D. and Wang, S.C. Investigation of enzymatic C-P bond formation using multiple quantum HCP nuclear magnetic resonance spectroscopy. Magn. Reson. Chem. 53 (2015) 267-272. [PMID: 25594737]