title: Structure of the imipenem-hydrolyzing class A beta-lactamase SME-1 from Serratia marcescens.
abstract: The structure of the beta-lactamase SME-1 from Serratia marcescens, a class A enzyme characterized by its significant activity against imipenem, has been determined to 2.13 A resolution. The overall structure of SME-1 is similar to that of other class A beta-lactamases. In the active-site cavity, most of the residues found in SME-1 are conserved among class A beta-lactamases, except at positions 104, 105 and 237, where a tyrosine, a histidine and a serine are found, respectively, and at position 238, which is occupied by a cysteine forming a disulfide bridge with the other cysteine residue located at position 69. The crucial role played by this disulfide bridge in SME-1 was confirmed by site-directed mutagenesis of Cys69 to Ala, which resulted in a mutant unable to confer resistance to imipenem and all other beta-lactam antibiotics tested. Another striking structural feature found in SME-1 was the short distance separating the side chains of the active serine residue at position 70 and the strictly conserved glutamate at position 166, which is up to 1.4 A shorter in SME-1 compared with other class A beta-lactamases. Consequently, the SME-1 structure cannot accommodate the essential catalytic water molecule found between Ser70 and Glu166 in the other class A beta-lactamases described so far, suggesting that a significant conformational change may be necessary in SME-1 to properly position the hydrolytic water molecule involved in the hydrolysis of the acyl-enzyme intermediate.
authors.affiliation: Laboratoire de Recherche Moléculaire sur les Antibiotiques (LRMA), INSERM EMI0004, Faculté de Médecine Pitié-Salpêtrière, Université Pierre et Marie Curie, 75634 Paris CEDEX 13, France.
authors.forename: Wladimir
authors.initials: W
authors.lastname: Sougakoff
authors.forename: Guillaume
authors.initials: G
authors.lastname: L'Hermite
authors.forename: Lucile
authors.initials: L
authors.lastname: Pernot
authors.forename: Thierry
authors.initials: T
authors.lastname: Naas
authors.forename: Valérie
authors.initials: V
authors.lastname: Guillet
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
authors.forename: Vincent
authors.initials: V
authors.lastname: Jarlier
authors.forename: Jean
authors.initials: J
authors.lastname: Delettré
mesh_terms: D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000235:genetics; D006868:Hydrolysis; D015378:Imipenem / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012706:Serratia marcescens / Q000201:enzymology*; D001618:beta-Lactamases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D015378:Imipenem; C094219:beta-lactamase Sme-1; D001618:beta-Lactamases; D003545:Cysteine; D000409:Alanine