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.
He
M M
MM
Howard Hughes Medical Institute, Institute of Molecular Biology, Department of Physics, 1229 University of Oregon, Eugene, Oregon 97403-1229, USA.
Clugston
S L
SL
Honek
J F
JF
Matthews
B W
BW
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