This enzyme has been implicated in the formation of the acetamido moiety (sugar-NC(=NH)CH3) which is found on some exopolysaccharides and is positively charged at neutral pH. The reaction involves ligation of ammonia with a sugar N-acetyl group, displacing water. In E. coli (O145 strain) and Pseudomonas aeruginosa (O12 strain) this gene is known as wbuX and ifnA respectively and likely acts on sialic acid [1]. In Campylobacter jejuni, the gene is known as pseA and acts on pseudaminic acid in the process of flagellin glycosylation [2]. In other Pseudomonas strains and various organisms it is unclear what the identity of the sugar substrate is, and in fact, the phylogenetic tree of this family sports a considerably deep branching suggestive of possible major differences in substrate structure. Nevertheless, the family is characterized by a conserved tetracysteine motif (CxxC.....[GN]xCxxC) possibly indicative of a metal binding site, as well as an invariable contextual association with homologs of the HisH and HisF proteins known as WbuY and WbuZ, respectively. These two proteins are believed to supply the enzyme with ammonium by hydrolysis of glutamine and delivery through an ammonium conduit [3].
- Date:
- 2019-09-10