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Lu B, Liao SM, Liang SJ, Li JX, Liu XH, Huang RB, Zhou GP. NMR Studies of the Interactions between Sialyllactoses and the Polysialytransferase Domain for Polysialylation Inhibition. Curr Issues Mol Biol 2024; 46:5682-5700. [PMID: 38921011 PMCID: PMC11201969 DOI: 10.3390/cimb46060340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2024] [Revised: 04/30/2024] [Accepted: 05/26/2024] [Indexed: 06/27/2024] Open
Abstract
It is known that sialyllactose (SL) in mammalians is a major source of sialic acid (Sia), which can further form cytidine monophosphate sialic acid (CMP-Sia), and the final product is polysialic acid (polySia) using polysialyltransferases (polySTs) on the neural cell adhesion molecule (NCAM). This process is called NCAM polysialylation. The overexpression of polysialylation is strongly related to cancer cell migration, invasion, and metastasis. In order to inhibit the overexpression of polysialylation, in this study, SL was selected as an inhibitor to test whether polysialylation could be inhibited. Our results suggest that the interactions between the polysialyltransferase domain (PSTD) in polyST and CMP-Siaand the PSTD and polySia could be inhibited when the 3'-sialyllactose (3'-SL) or 6'-sialyllactose (6'-SL) concentration is about 0.5 mM or 6'-SL and 3 mM, respectively. The results also show that SLs (particularly for 3'-SL) are the ideal inhibitors compared with another two inhibitors, low-molecular-weight heparin (LMWH) and cytidine monophosphate (CMP), because 3'-SL can not only be used to inhibit NCAM polysialylation, but is also one of the best supplements for infant formula and the gut health system.
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Affiliation(s)
- Bo Lu
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
| | - Si-Ming Liao
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
| | - Shi-Jie Liang
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
| | - Jian-Xiu Li
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
| | - Xue-Hui Liu
- Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China;
| | - Ri-Bo Huang
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
- Life Science and Technology College, Guangxi University, Nanning 530004, China
- Rocky Mount Life Science Institute, Rocky Mount, NC 27804, USA
| | - Guo-Ping Zhou
- National Engineering Research Center for Non-Food Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning 530007, China; (B.L.); (S.-M.L.); (S.-J.L.); (J.-X.L.)
- Rocky Mount Life Science Institute, Rocky Mount, NC 27804, USA
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Gustafsson R, Eckhard U, Ye W, Enbody ED, Pettersson M, Jemth P, Andersson L, Selmer M. Structure and Characterization of Phosphoglucomutase 5 from Atlantic and Baltic Herring-An Inactive Enzyme with Intact Substrate Binding. Biomolecules 2020; 10:E1631. [PMID: 33287293 PMCID: PMC7761743 DOI: 10.3390/biom10121631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Revised: 11/27/2020] [Accepted: 11/30/2020] [Indexed: 12/31/2022] Open
Abstract
Phosphoglucomutase 5 (PGM5) in humans is known as a structural muscle protein without enzymatic activity, but detailed understanding of its function is lacking. PGM5 belongs to the alpha-D-phosphohexomutase family and is closely related to the enzymatically active metabolic enzyme PGM1. In the Atlantic herring, Clupea harengus, PGM5 is one of the genes strongly associated with ecological adaptation to the brackish Baltic Sea. We here present the first crystal structures of PGM5, from the Atlantic and Baltic herring, differing by a single substitution Ala330Val. The structure of PGM5 is overall highly similar to structures of PGM1. The structure of the Baltic herring PGM5 in complex with the substrate glucose-1-phosphate shows conserved substrate binding and active site compared to human PGM1, but both PGM5 variants lack phosphoglucomutase activity under the tested conditions. Structure comparison and sequence analysis of PGM5 and PGM1 from fish and mammals suggest that the lacking enzymatic activity of PGM5 is related to differences in active-site loops that are important for flipping of the reaction intermediate. The Ala330Val substitution does not alter structure or biophysical properties of PGM5 but, due to its surface-exposed location, could affect interactions with protein-binding partners.
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Affiliation(s)
- Robert Gustafsson
- Department of Cell and Molecular Biology, Uppsala University, BMC, Box 596, SE-751 24 Uppsala, Sweden; (R.G.); (U.E.)
| | - Ulrich Eckhard
- Department of Cell and Molecular Biology, Uppsala University, BMC, Box 596, SE-751 24 Uppsala, Sweden; (R.G.); (U.E.)
| | - Weihua Ye
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, SE-751 23 Uppsala, Sweden; (W.Y.); (E.D.E.); (M.P.); (P.J.); (L.A.)
| | - Erik D. Enbody
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, SE-751 23 Uppsala, Sweden; (W.Y.); (E.D.E.); (M.P.); (P.J.); (L.A.)
| | - Mats Pettersson
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, SE-751 23 Uppsala, Sweden; (W.Y.); (E.D.E.); (M.P.); (P.J.); (L.A.)
| | - Per Jemth
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, SE-751 23 Uppsala, Sweden; (W.Y.); (E.D.E.); (M.P.); (P.J.); (L.A.)
| | - Leif Andersson
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, SE-751 23 Uppsala, Sweden; (W.Y.); (E.D.E.); (M.P.); (P.J.); (L.A.)
- Department of Veterinary Integrative Biosciences, Texas A & M University, College Station, TX 77843, USA
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, SE-75007 Uppsala, Sweden
| | - Maria Selmer
- Department of Cell and Molecular Biology, Uppsala University, BMC, Box 596, SE-751 24 Uppsala, Sweden; (R.G.); (U.E.)
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3
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Stiers KM, Beamer LJ. Assessment and Impacts of Phosphorylation on Protein Flexibility of the α-d-Phosphohexomutases. Methods Enzymol 2018; 607:241-267. [DOI: 10.1016/bs.mie.2018.04.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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4
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Multiple Ligand-Bound States of a Phosphohexomutase Revealed by Principal Component Analysis of NMR Peak Shifts. Sci Rep 2017; 7:5343. [PMID: 28706231 PMCID: PMC5509744 DOI: 10.1038/s41598-017-05557-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 05/31/2017] [Indexed: 11/08/2022] Open
Abstract
Enzymes sample multiple conformations during their catalytic cycles. Chemical shifts from Nuclear Magnetic Resonance (NMR) are hypersensitive to conformational changes and ensembles in solution. Phosphomannomutase/phosphoglucomutase (PMM/PGM) is a ubiquitous four-domain enzyme that catalyzes phosphoryl transfer across phosphohexose substrates. We compared states the enzyme visits during its catalytic cycle. Collective responses of Pseudomonas PMM/PGM to phosphosugar substrates and inhibitor were assessed using NMR-detected titrations. Affinities were estimated from binding isotherms obtained by principal component analysis (PCA). Relationships among phosphosugar-enzyme associations emerge from PCA comparisons of the titrations. COordiNated Chemical Shifts bEhavior (CONCISE) analysis provides novel discrimination of three ligand-bound states of PMM/PGM harboring a mutation that suppresses activity. Enzyme phosphorylation and phosphosugar binding appear to drive the open dephosphorylated enzyme to the free phosphorylated state, and on toward ligand-closed states. Domain 4 appears central to collective responses to substrate and inhibitor binding. Hydrogen exchange reveals that binding of a substrate analogue enhances folding stability of the domains to a uniform level, establishing a globally unified structure. CONCISE and PCA of NMR spectra have discovered novel states of a well-studied enzyme and appear ready to discriminate other enzyme and ligand binding states.
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Stiers KM, Muenks AG, Beamer LJ. Biology, Mechanism, and Structure of Enzymes in the α-d-Phosphohexomutase Superfamily. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2017; 109:265-304. [PMID: 28683921 PMCID: PMC5802415 DOI: 10.1016/bs.apcsb.2017.04.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Enzymes in the α-d-phosphohexomutases superfamily catalyze the reversible conversion of phosphosugars, such as glucose 1-phosphate and glucose 6-phosphate. These reactions are fundamental to primary metabolism across the kingdoms of life and are required for a myriad of cellular processes, ranging from exopolysaccharide production to protein glycosylation. The subject of extensive mechanistic characterization during the latter half of the 20th century, these enzymes have recently benefitted from biophysical characterization, including X-ray crystallography, NMR, and hydrogen-deuterium exchange studies. This work has provided new insights into the unique catalytic mechanism of the superfamily, shed light on the molecular determinants of ligand recognition, and revealed the evolutionary conservation of conformational flexibility. Novel associations with inherited metabolic disease and the pathogenesis of bacterial infections have emerged, spurring renewed interest in the long-appreciated functional roles of these enzymes.
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Affiliation(s)
| | | | - Lesa J Beamer
- University of Missouri, Columbia, MO, United States.
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Stiers KM, Graham AC, Kain BN, Beamer LJ. Asp263 missense variants perturb the active site of human phosphoglucomutase 1. FEBS J 2017; 284:937-947. [PMID: 28117557 DOI: 10.1111/febs.14025] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 12/31/2016] [Accepted: 01/19/2017] [Indexed: 11/26/2022]
Abstract
The enzyme phosphoglucomutase 1 (PGM1) plays a central role in glucose homeostasis. Clinical studies have identified mutations in human PGM1 as the cause of PGM1 deficiency, an inherited metabolic disease. One residue, Asp263, has two known variants associated with disease: D263G and D263Y. Biochemical studies have shown that these mutants are soluble and well folded, but have significant catalytic impairment. To better understand this catalytic defect, we determined crystal structures of these two missense variants, both of which reveal a similar and indirect structural change due to the loss of a conserved salt bridge between Asp263 and Arg293. The arginine reorients into the active site, making interactions with residues responsible for substrate binding. Biochemical studies also show that the catalytic phosphoserine of the missense variants is more stable to hydrolysis relative to wild-type enzyme. The structural perturbation resulting from mutation of this single amino acid reveals the molecular mechanism underlying PGM1 deficiency in these missense variants. DATABASE Structural data are available in the PDB under the accession numbers 5JN5 and 5TR2.
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Affiliation(s)
- Kyle M Stiers
- Biochemistry Department, University of Missouri, Columbia, MO, USA
| | - Abigail C Graham
- Biochemistry Department, University of Missouri, Columbia, MO, USA
| | - Bailee N Kain
- Biochemistry Department, University of Missouri, Columbia, MO, USA
| | - Lesa J Beamer
- Biochemistry Department, University of Missouri, Columbia, MO, USA
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Lee Y, Furdui C, Beamer LJ. Data on the phosphorylation state of the catalytic serine of enzymes in the α-D-phosphohexomutase superfamily. Data Brief 2016; 10:398-405. [PMID: 28050582 PMCID: PMC5192239 DOI: 10.1016/j.dib.2016.12.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 12/06/2016] [Accepted: 12/08/2016] [Indexed: 01/28/2023] Open
Abstract
Most enzymes in the α-D-phosphohexomutase superfamily catalyze the reversible conversion of 1- to 6-phosphosugars. They play important roles in carbohydrate and sugar nucleotide metabolism, and participate in the biosynthesis of polysaccharides, glycolipids, and other exoproducts. Mutations in genes encoding these enzymes are associated with inherited metabolic diseases in humans, including glycogen storage disease and congenital disorders of glycosylation. Enzymes in the superfamily share a highly conserved active site serine that participates in the multi-step phosphoryl transfer reaction. Here we provide data on the effects of various phosphosugar ligands on the phosphorylation of this serine, as monitored by electrospray ionization mass spectrometry (ESI-MS) data on the intact proteins. We also show data on the longevity of the phospho-enzyme under various solution conditions in one member of the superfamily from Pseudomonas aeruginosa, and present inhibition data for several ligands. These data should be useful for the production of homogeneous samples of phosphorylated or unphosphorylated proteins, which are essential for biophysical characterization of these enzymes.
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Affiliation(s)
- Yingying Lee
- Departments of Biochemistry and Chemistry, University of Missouri-Columbia, Columbia, MO 65211, United States
| | - Cristina Furdui
- Department of Internal Medicine, Wake Forest University Health Sciences, Winston-Salem, NC, USA
| | - Lesa J. Beamer
- Departments of Biochemistry and Chemistry, University of Missouri-Columbia, Columbia, MO 65211, United States
- Corresponding author.
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Xu J, Lee Y, Beamer LJ, Van Doren SR. Phosphorylation in the catalytic cleft stabilizes and attracts domains of a phosphohexomutase. Biophys J 2015; 108:325-37. [PMID: 25606681 DOI: 10.1016/j.bpj.2014.12.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 11/22/2014] [Accepted: 12/03/2014] [Indexed: 11/18/2022] Open
Abstract
Phosphorylation can modulate the activities of enzymes. The phosphoryl donor in the catalytic cleft of α-D-phosphohexomutases is transiently dephosphorylated while the reaction intermediate completes a 180° reorientation within the cleft. The phosphorylated form of 52 kDa bacterial phosphomannomutase/phosphoglucomutase is less accessible to dye or protease, more stable to chemical denaturation, and widely stabilized against NMR-detected hydrogen exchange across the core of domain 3 to juxtaposed domain 4 (each by ≥ 1.3 kcal/mol) and parts of domains 1 and 2. However, phosphorylation accelerates hydrogen exchange in specific regions of domains 1 and 2, including a metal-binding residue in the active site. Electrostatic field lines reveal attraction across the catalytic cleft between phosphorylated Ser-108 and domain 4, but repulsion when Ser-108 is dephosphorylated. Molecular dynamics (MD) simulated the dephosphorylated form to be expanded due to enhanced rotational freedom of domain 4. The contacts and fluctuations of the MD trajectories enabled correct simulation of more than 80% of sites that undergo either protection or deprotection from hydrogen exchange due to phosphorylation. Electrostatic attraction in the phosphorylated enzyme accounts for 1) domain 4 drawing closer to domains 1 and 3; 2) decreased accessibility; and 3) increased stability within these domains. The electrostriction due to phosphorylation may help capture substrate, whereas the opening of the cleft upon transient dephosphorylation allows rotation of the intermediate. The long-range effects of phosphorylation on hydrogen exchange parallel reports on protein kinases, suggesting a conceptual link among these multidomain, phosphoryl transfer enzymes.
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Affiliation(s)
- Jia Xu
- Department of Biochemistry, University of Missouri, Columbia, Missouri
| | - Yingying Lee
- Department of Biochemistry, University of Missouri, Columbia, Missouri
| | - Lesa J Beamer
- Department of Biochemistry, University of Missouri, Columbia, Missouri
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Wei Y, Marcink TC, Xu J, Sirianni AG, Sarma AVS, Prior SH, Beamer LJ, Van Doren SR. Chemical shift assignments of domain 4 from the phosphohexomutase from Pseudomonas aeruginosa suggest that freeing perturbs its coevolved domain interface. BIOMOLECULAR NMR ASSIGNMENTS 2014; 8:329-333. [PMID: 23893395 PMCID: PMC3905050 DOI: 10.1007/s12104-013-9511-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 07/18/2013] [Indexed: 06/02/2023]
Abstract
A domain needed for the catalytic efficiency of an enzyme model of simple processivity and domain-domain interactions has been characterized by NMR. This domain 4 from phosphomannomutase/phosphoglucomutase (PMM/PGM) closes upon glucose phosphate and mannose phosphate ligands in the active site, and can modestly reconstitute activity of enzyme truncated to domains 1-3. This enzyme supports biosynthesis of the saccharide-derived virulence factors (rhamnolipids, lipopolysaccharides, and alginate) of the opportunistic bacterial pathogen Pseudomonas aeruginosa. (1)H, (13)C, and (15)N NMR chemical shift assignments of domain 4 of PMM/PGM suggest preservation and independence of its structure when separated from domains 1-3. The face of domain 4 that packs with domain 3 is perturbed in NMR spectra without disrupting this fold. The perturbed residues overlap both the most highly coevolved positions in the interface and residues lining a cavity at the domain interface.
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Lee Y, Villar MT, Artigues A, Beamer LJ. Promotion of enzyme flexibility by dephosphorylation and coupling to the catalytic mechanism of a phosphohexomutase. J Biol Chem 2014; 289:4674-82. [PMID: 24403075 DOI: 10.1074/jbc.m113.532226] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) from Pseudomonas aeruginosa catalyzes an intramolecular phosphoryl transfer across its phosphosugar substrates, which are precursors in the synthesis of exoproducts involved in bacterial virulence. Previous structural studies of PMM/PGM have established a key role for conformational change in its multistep reaction, which requires a dramatic 180° reorientation of the intermediate within the active site. Here hydrogen-deuterium exchange by mass spectrometry and small angle x-ray scattering were used to probe the conformational flexibility of different forms of PMM/PGM in solution, including its active, phosphorylated state and the unphosphorylated state that occurs transiently during the catalytic cycle. In addition, the effects of ligand binding were assessed through use of a substrate analog. We found that both phosphorylation and binding of ligand produce significant effects on deuterium incorporation. Phosphorylation of the conserved catalytic serine has broad effects on residues in multiple domains and is supported by small angle x-ray scattering data showing that the unphosphorylated enzyme is less compact in solution. The effects of ligand binding are generally manifested near the active site cleft and at a domain interface that is a site of conformational change. These results suggest that dephosphorylation of the enzyme may play two critical functional roles: a direct role in the chemical step of phosphoryl transfer and secondly through propagation of structural flexibility. We propose a model whereby increased enzyme flexibility facilitates the reorientation of the reaction intermediate, coupling changes in structural dynamics with the unique catalytic mechanism of this enzyme.
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Lee Y, Mehra-Chaudhary R, Furdui C, Beamer LJ. Identification of an essential active-site residue in the α-D-phosphohexomutase enzyme superfamily. FEBS J 2013; 280:2622-32. [PMID: 23517223 DOI: 10.1111/febs.12249] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 03/12/2013] [Accepted: 03/14/2013] [Indexed: 12/01/2022]
Abstract
UNLABELLED Enzymes in the α-d-phosphohexomutase superfamily catalyze the conversion of 1-phosphosugars to their 6-phospho counterparts. Their phosphoryl transfer reaction has long been proposed to require general acid-base catalysts, but candidate residues for these key roles have not been identified. In this study, we show through mutagenesis and kinetic studies that a histidine (His329) in the active site is critical for enzyme activity in a well-studied member of the superfamily, phosphomannomutase/phosphoglucomutase from Pseudomonas aeruginosa. Crystallographic characterization of an H329A mutant protein showed no significant changes from the wild-type enzyme, excluding structural disruption as the source of its compromised activity. Mutation of the structurally analogous lysine residue in a related protein, phosphoglucomutase from Salmonella typhimurium, also results in significant catalytic impairment. Analyses of protein-ligand complexes of the P. aeruginosa enzyme show that His329 is appropriately positioned to abstract a proton from the O1/O6 hydroxyl of the phosphosugar substrates, and thus may serve as the general base in the reaction. Histidine is strongly conserved at this position in many proteins in the superfamily, and lysine is also often conserved at a structurally corresponding position, particularly in the phosphoglucomutase enzyme sub-group. These studies shed light on the mechanism of this important enzyme superfamily, and may facilitate the design of mechanism-based inhibitors. DATABASE Structural data have been deposited in the Protein Data Bank with accession number 4IL8.
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Affiliation(s)
- Yingying Lee
- Chemistry Department, University of Missouri, Columbia, MO 65211, USA
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12
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Conservation of functionally important global motions in an enzyme superfamily across varying quaternary structures. J Mol Biol 2012; 423:831-46. [PMID: 22935436 DOI: 10.1016/j.jmb.2012.08.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 08/16/2012] [Accepted: 08/17/2012] [Indexed: 11/21/2022]
Abstract
The α-d-phosphohexomutase superfamily comprises enzymes involved in carbohydrate metabolism that are found in all kingdoms of life. Recent biophysical studies have shown for the first time that several of these enzymes exist as dimers in solution, prompting an examination of the oligomeric state of all proteins of known structure in the superfamily (11 different proteins; 31 crystal structures) via computational and experimental analyses. We find that these proteins range in quaternary structure from monomers to tetramers, with 6 of the 11 known structures being likely oligomers. The oligomeric state of these proteins not only is associated in some cases with enzyme subgroup (i.e., substrate specificity) but also appears to depend on domain of life, with the two archaeal proteins existing as higher-order oligomers. Within the oligomers, three distinct interfaces are observed, one of which is found in both archaeal and bacterial proteins. Normal mode analysis shows that the topological arrangement of the oligomers permits domain 4 of each protomer to move independently as required for catalysis. Our analysis suggests that the advantages associated with protein flexibility in this enzyme family are of sufficient importance to be maintained during the evolution of multiple independent oligomers. This study is one of the first showing that global motions may be conserved not only within protein families but also across members of a superfamily with varying oligomeric structures.
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