Determination of the structure of Escherichia coli glyoxalase I suggests a structural basis for differential metal activation.
The metalloenzyme glyoxalase I (GlxI) converts the nonenzymatically produced hemimercaptal of cytotoxic methylglyoxal and glutathione to nontoxic S-D-lactoylglutathione. Human GlxI, for which the structure is known, is active in the presence of Zn(2+). Unexpectedly, the Escherichia coli enzyme is inactive in the presence of Zn(2+) and is maximally active with Ni(2+). To understand this difference in metal activation and also to obtain a representative of the bacterial enzymes, the structure of E. coli Ni(2+)-GlxI has been determined. Structures have also been determined for the apo enzyme as well as complexes with Co(2+), Cd(2+), and Zn(2+). It is found that each of the protein-metal complexes that is catalytically active has octahedral geometry. This includes the complexes of the E. coli enzyme with Ni(2+), Co(2+), and Cd(2+), as well as the structures reported for the human Zn(2+) enzyme. Conversely, the complex of the E. coli enzyme with Zn(2+) has trigonal bipyramidal coordination and is inactive. This mode of coordination includes four protein ligands plus a single water molecule. In contrast, the coordination in the active forms of the enzyme includes two water molecules bound to the metal ion, suggesting that this may be a key feature of the catalytic mechanism. A comparison of the human and E. coli enzymes suggests that there are differences between the active sites that might be exploited for therapeutic use.
Howard Hughes Medical Institute, Institute of Molecular Biology, Department of Physics, 1229 University of Oregon, Eugene, Oregon 97403-1229, USA.
M M
MM
He
S L
SL
Clugston
J F
JF
Honek
B W
BW
Matthews
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002413:Cations, Divalent; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D006801:Humans; D007791:Lactoylglutathione Lyase / Q000737:chemistry / Q000378:metabolism*; D008670:Metals / Q000737:chemistry / Q000378:metabolism*; D009532:Nickel / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
D001426:Bacterial Proteins; D002413:Cations, Divalent; D008670:Metals; D009532:Nickel; D007791:Lactoylglutathione Lyase; D015032:Zinc