Purification, crystallization and diffraction studies of the methyltransferases BT_2972 and BVU_3255 from antibiotic-resistant pathogens of the genus Bacteroides from the human intestine

The methyltransferases BT_2972 and BVU_3255 from two different Bacteroides species that are antibiotic-resistant pathogens from the human intestine were cloned, overexpressed and purified, yielding approximately 120 mg of each protein from 1 l culture. Apo BT_2972 and BVU_3255 and their complexes with S-adenosylmethionine or S-adenosylhomocysteine were crystallized in four different crystal forms using the hanging-drop vapour-diffusion method. These crystals diffracted to resolutions ranging from 2.8 to 2.2 Å. Sequence analysis suggested that the two proteins are homologous small-molecule methyltransferases.