The crystal structure of rabbit phosphoglucose isomerase complexed with 5-phospho- d -arabinonohydroxamic acid

Abstract

Phosphoglucose isomerase (EC 5.3.1.9) catalyzes the second step in glycolysis, the reversible isomerization of D-glucose 6-phosphate to D-fructose 6-phosphate. The reaction mechanism involves acid-base catalysis with proton transfer and proceeds through a cis-enediol(ate) intermediate. 5-Phospho-D-arabinonohydroxamic acid (5PAH) is a synthetic small molecule that resembles the reaction intermediate, differing only in that it has a nitrogen atom in place of C1. Hence, 5PAH is the best inhibitor of the isomerization reaction reported to date with a Ki of 2 ؋ 10 ؊7 M. Here we report the crystal structure of rabbit phosphoglucose isomerase complexed with 5PAH at 1.9 Å resolution. The interaction of 5PAH with amino acid residues in the enzyme active site supports a model of the catalytic mechanism in which Glu-357 transfers a proton between C1 and C2 and Arg-272 helps stabilize the intermediate. It also suggests a mechanism for proton transfer between O1 and O2. P hosphoglucose isomerase (PGI; EC 5.3.1.9) is a cytosolic glycolytic enzyme that catalyzes the reversible isomerization of D-glucose 6-phosphate (G6P) to D-fructose 6-phosphate (F6P). In addition to isomerase activity, PGI has been shown to display anomerase activity between pyranose anomers of G6P (1), between furanose anomers of F6P (2), and between those of D-mannose 6-phosphate (3), as well as C-2-epimerase activity on G6P (4). It also has roles in protein glycosylation, gluconeogenesis, and the pentose phosphate pathway (5). This central role in the metabolism of phosphorylated sugars explains the strong impact of PGI deficiency in humans (6, 7), as well as the interest as a therapeutic target in parasite metabolism (8). The PGI polypeptide chain, or perhaps a variation thereof, also has extracellular roles as neuroleukin, autocrine motility factor, and differentiation and maturation mediator (9-12). These proteins promote antibody secretion by mononuclear cells, tumor cell motility, and differentiation of leukemia cells and a promyelocytic cell line (HL-60 cells), respectively. More recently, PGI has also been identified as the antigen involved in rheumatoid arthritis of a mouse line (13), as a specific inhibitor toward myofibril-bound serine proteinase (14), and as the surface antigen involved in sperm agglutination (15). Because very little is known about how PGI is precisely involved in these various biological processes, this moonlighting protein (16) has been the subject of intense investigations.Biochemical characterization of PGI began over 50 years ago and includes inhibitor studies (1,(17)(18)(19)(20)(21)(22)(23)(24)(25), labeling studies (26-32), solvent exchange (33, 34), mutagenesis (35,36), and pH profile studies (20,37). A proposed multistep catalytic mechanism includes a ring-opening step followed by an isomerization step. The isomerization step proceeds via general acid-base catalysis with proton transfer. In the G6P to F6P direction, abstraction of the proton from C2 by an active site amino acid residue yields a 1,2-cis-enediol(ate) in...

Competitive Inhibitors of Mycobacterium tuberculosis Ribose-5-phosphate Isomerase B Reveal New Information about the Reaction Mechanism

“…6). As reported previously for Glu 165 in the triose-phosphate isomerase (TIM)-phosphoglycolohydroxamic acid complex structure (20), and in contrast to Glu 357 in the PGI-5-phospho-D-arabinonohydroxamic acid structure (21), the plane of the carboxylate moiety of Glu 75 is roughly perpendicular to the plane of the 4PEH hydroxamic function (Fig. 7).…”

Triosephosphate isomerase: a highly evolved biocatalyst

“…TIM is highly specific for the C3-sugar phosphates DHAP and D-GAP. Other sugar phosphate isomerases which use the same proton transfer mechanism [90] are, for example, D-ribose-5-phosphate isomerase (RPI) [91] and phosphoglucose isomerase (PGI) [92]. These two enzymes catalyse the same reaction as TIM, but the substrate is, respectively, a C5-sugar phosphate and a C6-sugar phosphate.…”

Bifunctional Phosphoglucose/Phosphomannose Isomerases from the Archaea Aeropyrum pernix and Thermoplasma acidophilum Constitute a Novel Enzyme Family within the Phosphoglucose Isomerase Superfamily

“…PGI structures have been solved from a variety of mammalian sources and from B. stearothermophilus in native, inhibitor, and substrate (F6P)-bound forms (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). CD spectra analysis and secondary structure predictions suggest a similar fold of the PGI/PMI from A. pernix and T. acidophilum and e.g.…”