This family consists of several bacterial and one archaeal methionine biosynthesis MetW proteins. Biosynthesis of methionine from homoserine in Pseudomonas putida takes place in three steps. The first step is the acylation of homoserine to yield an acyl-L-homoserine. This reaction is catalysed by the products of the metXW genes and is equivalent to the first step in enterobacteria, gram-positive bacteria and fungi, except that in these microorganisms the reaction is catalysed by a single polypeptide (the product of the metA gene in Escherichia coli and the met5 gene product in Neurospora crassa). In Pseudomonas putida, as in gram-positive bacteria and certain fungi, the second and third steps are a direct sulfhydrylation that converts the O-acyl-L-homoserine into homocysteine and further methylation to yield methionine. The latter reaction can be mediated by either of the two methionine synthetases present in the cells [1].

1: The methionine biosynthetic pathway from homoserine in Pseudomonas putida involves the metW, metX, metZ, metH and metE gene products. Alaminos M, Ramos JL; Arch Microbiol 2001;176:151-154. PMID:11479715