The L1 metallo-beta-lactamase from Stenotrophomonas maltophilia is unique among beta-lactamases in that it is tetrameric. S. maltophilia has emerged as a significant hospital-derived pathogen of immunocompromised hosts such as cancer, cystic fibrosis and transplant patients. L1 is localised to the periplasm and hydrolyses carbapenem drugs, conferring antibiotic resistance.
L1 is a Class B1 metallo-beta-lactamases as it binds two Zn(II) ions for the hydrolytic reaction, but its Zn2 binding site is different to most B1 type enzymes (it is also known as an L1 type 3 beta-lactamse).
Defined by 7 residues: HIS:A-84HIS:A-86ASP:A-88HIS:A-89HIS:A-160TYR:A-191HIS:A-225