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. Cannot use D-histidine in place of 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 Interacts with CntM. 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. Cells lacking this gene are unable to synthesize pseudopaline and are impaired in their ability to import nickel in a minimal media, supplemented or not with nickel. Under more stringent conditions where a chelator such as EDTA is added to a minimal succinate (MS) medium, a condition that presumably mimics the chelating environment prevailing within a host or in airway mucus secretion (AMS), the deletion mutant strain is unable to import zinc, therefore reconciling the regulation of this operon by zinc with its function as a zinc importer operating in metal scarce conditions. Belongs to the methyltransferase superfamily. CntL family.