The crystal structure of mouse phosphoglucose isomerase at 1.6A resolution and its complex with glucose 6-phosphate reveals the catalytic mechanism of sugar ring opening.
Phosphoglucose isomerase (PGI) is an enzyme of glycolysis that interconverts glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P) but, outside the cell, is a multifunctional cytokine. High-resolution crystal structures of the enzyme from mouse have been determined in native form and in complex with the inhibitor erythrose 4-phosphate, and with the substrate glucose 6-phosphate. In the substrate-bound structure, the glucose sugar is observed in both straight-chain and ring forms. This structure supports a specific role for Lys518 in enzyme-catalyzed ring opening and we present a "push-pull" mechanism in which His388 breaks the O5-C1 bond by donating a proton to the ring oxygen atom and, simultaneously, Lys518 abstracts a proton from the C1 hydroxyl group. The reverse occurs in ring closure. The transition from ring form to straight-chain substrate is achieved through rotation of the C3-C4 bond, which brings the C1-C2 region into close proximity to Glu357, the base catalyst for the isomerization step. The structure with G6P also explains the specificity of PGI for glucose 6-phosphate over mannose 6-isomerase (M6P). To isomerize M6P to F6P requires a rotation of its C2-C3 bond but in PGI this is sterically blocked by Gln511.
Solomons
J T Graham
JT
Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
Zimmerly
Ella M
EM
Burns
Suzanne
S
Krishnamurthy
N
N
Swan
Michael K
MK
Krings
Sandra
S
Muirhead
Hilary
H
Chirgwin
John
J
Davies
Christopher
C
D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D005636:Fructosephosphates / Q000737:chemistry / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000737:chemistry / Q000378:metabolism; D005956:Glucose-6-Phosphate Isomerase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D051379:Mice; D008958:Models, Molecular; D011487:Protein Conformation; D011817:Rabbits; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D013379:Substrate Specificity; D013403:Sugar Phosphates / Q000737:chemistry / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005636:Fructosephosphates; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D013403:Sugar Phosphates; D019298:Glucose-6-Phosphate; C026959:erythrose 4-phosphate; C027618:fructose-6-phosphate; D005956:Glucose-6-Phosphate Isomerase