Mutational analysis of the two zinc-binding sites of the Bacillus cereus 569/H/9 metallo-beta-lactamase.
The metallo-beta-lactamase BcII from Bacillus cereus 569/H/9 possesses a binuclear zinc centre. The mono-zinc form of the enzyme displays an appreciably high activity, although full efficiency is observed for the di-zinc enzyme. In an attempt to assign the involvement of the different zinc ligands in the catalytic properties of BcII, individual substitutions of selected amino acids were generated. With the exception of His(116)-->Ser (H116S), C221A and C221S, the mono- and di-zinc forms of all the other mutants were poorly active. The activity of H116S decreases by a factor of 10 when compared with the wild type. The catalytic efficiency of C221A and C221S was zinc-dependent. The mono-zinc forms of these mutants exhibited a low activity, whereas the catalytic efficiency of their respective di-zinc forms was comparable with that of the wild type. Surprisingly, the zinc contents of the mutants and the wild-type BcII were similar. These data suggest that the affinity of the beta-lactamase for the metal was not affected by the substitution of the ligand. The pH-dependence of the H196S catalytic efficiency indicates that the zinc ions participate in the hydrolysis of the beta-lactam ring by acting as a Lewis acid. The zinc ions activate the catalytic water molecule, but also polarize the carbonyl bond of the beta-lactam ring and stabilize the development of a negative charge on the carbonyl oxygen of the tetrahedral reaction intermediate. Our studies also demonstrate that Asn(233) is not directly involved in the interaction with the substrates.
de Seny
Dominique
D
Centre d'Ingénierie des Protéines, Institut de Chimie B6, Université de Liège, Sart-Tilman, B-4000 Liège, Belgium.
Prosperi-Meys
Christelle
C
Bebrone
Carine
C
Rossolini
Gian Maria
GM
Page
Michael I
MI
Noel
Philippe
P
Frère
Jean-Marie
JM
Galleni
Moreno
M
D001409:Bacillus cereus / Q000201:enzymology*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D020134:Catalytic Domain; D002942:Circular Dichroism; D004252:DNA Mutational Analysis; D004926:Escherichia coli; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D015032:Zinc / Q000378:metabolism*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism*
C455979:beta-lactamase BcII; D001618:beta-Lactamases; D015032:Zinc