Catalyzes the nucleophilic attack of one alpha-aminobutanoate moiety from SAM onto L-histidine to produce the intermediate (2S)-2-amino-4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}butanoate. Functions in the biosynthesis of the metallophore pseudopaline, which is involved in the acquisition of nickel and zinc, and thus enables bacterial growth inside the host, where metal access is limited. Therefore, this enzyme probably contributes to Pseudomonas virulence. Appears to be specific for L-histidine as substrate. L-histidine + S-adenosyl-L-methionine = (2S)-2-amino-4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}butanoate + H(+) + S-methyl-5'-thioadenosine kcat is 1.07 min(-1) (at pH 8 and 22 degrees Celsius). Is part of the operon cntOLMI that is negatively regulated by zinc level through the Zur repressor, which leads to transcriptional activation of this operon under zinc depletion (PubMed:28898501). Highly induced in response to airway mucus secretions (AMS) treatment (PubMed:26446565). Belongs to the methyltransferase superfamily. CntL family.