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 yersinopine, which is involved in metal acquisition and thus enables bacterial growth inside the host, where metal access is limited. Therefore, this enzyme probably contributes to Yersinia virulence. 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 Belongs to the methyltransferase superfamily. CntL family.