Cloning and Purification of (His) 6 -Tagged Recombinant NAGK Proteins of L. hongkongensis HLHK9 Cloning and purification of (His) 6 -tagged recombinant NAGK proteins of L. hongkongensis HLHK9 was performed according to our previous publications, with modifications [53, 55] . To produce plasmids for protein purification, primers (59-GGAATTCCA-TATGCTGCTTGCAGACGCCC -39 and 59-GGAATTCCA-TATGTCAGGCTGCGCGGATCAT -39 for argB-20 and 59-GGAATTCCATATGGTTATTCAATCTGAAGT -39 and 59-GGAATTCCATATGTCAGAGCGTGGTACAGAT -39 for argB-37) were used to amplify the genes encoding NAGK-20 and NAGK-37, respectively, by PCR. The sequence coding for amino acid residues of the complete NAGK-20 and NAGK-37 was amplified and cloned, respectively, into the NdeI site of expression vector pET-28b(+) (Novagen) in frame and downstream of the series of six histidine residues. The two recombinant NAGK proteins were expressed and purified using the Ni 2+ -loaded HiTrap Chelating System according to the manufacturer's instructions (GE Healthcare).