Involved in the biosynthesis of the antimetabolite L-2-amino-4-methoxy-trans-3-butenoic acid (AMB), a non-proteinogenic amino acid which is toxic for prokaryotes and eukaryotes (PubMed:20543073, PubMed:25814981). Adenylates L-alanine and loads it onto its peptidyl carrier domain via a thioester linkage to the phosphopanthetheine moiety. In addition, loads activated L-Ala in trans onto the second carrier domain of AmbE (PubMed:25814981). Can also activate L-Ser, Gly and D-Ala, albeit to a lower extent (PubMed:25814981). The condensation domain of AmbB probably condenses the activated L-Ala and the L-Glu loaded on AmbE to form a L-Glu-L-Ala dipeptide at the first carrier domain of AmbE (PubMed:25814981). ATP + holo-[peptidyl-carrier protein] + L-alanine = AMP + diphosphate + L-alanyl-[peptidyl-carrier protein] Expression is regulated by the PhoR-PhoB two-component system. Modular protein that contains an adenylation domain which activates the alanine residue into an aminoacyl-AMP ester, a peptidyl carrier protein domain which bears a phosphopantetheinyl arm to attach the activated alanine and a condensation domain involved in the condensation of this amino acid with a second amino acid bound at the carrier protein domain of another module. Mutation abolishes AMB production (PubMed:20543073, PubMed:23542643). Deletion of the gene almost abolishes the production of the quorum sensing signals 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) and N-butanoylhomoserine lactone (C4HSL), but it has no effect on the biosynthesis of the quorum sensing signal N-3-oxododecanoylhomoserine lactone (3OC12HSL) (PubMed:23542643). Deletion causes a substantial reduction in the production of the virulence factors pyocyanine and elastase, and it reduces bacterial virulence by about 32-40% (PubMed:23542643). Belongs to the NRP synthetase family. It was suggested by Lee et al that the amb cluster is involved in the biosynthesis of 2-(2-hydroxyphenyl)-thiazole-4-carbaldehyde (IQS), a cell-cell communication signal that modulates the production of AMB through the pqs and rhl quorum sensing systems (PubMed:23542643). The chemical structure of IQS indicates that this compound may be assembled from salicylate and cysteine. However, neither of the two peptide synthases encoded by the amb gene cluster present adenylation domains with a specificity for these substrates. It is thus highly implausible that IQS is specified by the amb gene cluster (PubMed:25814981).