1
|
Interaction studies of a protein and carbohydrate system using an integrated approach: a case study of the miniagrin-heparin system. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2018. [PMID: 29532137 DOI: 10.1007/s00249-018-1291-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The major challenges in biophysical characterization of human protein-carbohydrate interactions are obtaining monodispersed preparations of human proteins that are often post-translationally modified and lack of detection of carbohydrates by traditional detection systems. Light scattering (dynamic and static) techniques offer detection of biomolecules and their complexes based on their size and shape, and do not rely on chromophore groups (such as aromatic amino acid sidechains). In this study, we utilized dynamic light scattering, analytical ultracentrifugation and small-angle X-ray scattering techniques to investigate the solution properties of a complex resulting from the interaction between a 15 kDa heparin preparation and miniagrin, a miniaturized version of agrin. Results from dynamic light scattering, sedimentation equilibrium, and sedimentation velocity experiments signify the formation of a monodisperse complex with 1:1 stoichiometry, and low-resolution structures derived from the small-angle X-ray scattering measurements implicate an extended conformation for a side-by-side miniagrin‒heparin complex.
Collapse
|
2
|
Hall D, Harding SE. Foreword to 'Quantitative and analytical relations in biochemistry'-a special issue in honour of Donald J. Winzor's 80th birthday. Biophys Rev 2016; 8:269-277. [PMID: 28510020 PMCID: PMC5425807 DOI: 10.1007/s12551-016-0227-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 09/29/2016] [Indexed: 10/20/2022] Open
Abstract
The purpose of this special issue is to honour Professor Donald J. Winzor's long career as a researcher and scientific mentor, and to celebrate the milestone of his 80th birthday. Throughout his career, Don has been renowned for his development of clever approximations to difficult quantitative relations governing a range of biophysical measurements. The theme of this special issue, 'Quantitative and analytical relations in biochemistry', was chosen to reflect this aspect of Don's scientific approach.
Collapse
Affiliation(s)
- Damien Hall
- Research School of Chemistry, Australian National University, Acton, ACT, 2601, Australia.
- Institute for Protein Research, Osaka University, 3-1- Yamada-oka, Suita, Osaka, 565-0871, Japan.
| | - Stephen E Harding
- National Centre for Macromolecular Hydrodynamics, University of Nottingham Sutton Bonington Campus, Sutton Bonington, Leicestershire, LE12 5RD, UK.
| |
Collapse
|
3
|
Harding SE, Gillis RB, Adams GG. Assessing sedimentation equilibrium profiles in analytical ultracentrifugation experiments on macromolecules: from simple average molecular weight analysis to molecular weight distribution and interaction analysis. Biophys Rev 2016; 8:299-308. [PMID: 28003857 PMCID: PMC5135724 DOI: 10.1007/s12551-016-0232-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Accepted: 10/05/2016] [Indexed: 11/20/2022] Open
Abstract
Molecular weights (molar masses), molecular weight distributions, dissociation constants and other interaction parameters are fundamental characteristics of proteins, nucleic acids, polysaccharides and glycoconjugates in solution. Sedimentation equilibrium analytical ultracentrifugation provides a powerful method with no supplementary immobilization, columns or membranes required. It is a particularly powerful tool when used in conjunction with its sister technique, namely sedimentation velocity. Here, we describe key approaches now available and their application to the characterization of antibodies, polysaccharides and glycoconjugates. We indicate how major complications, such as thermodynamic non-ideality, can now be routinely dealt with, thanks to a great extent to the extensive contribution of Professor Don Winzor over several decades of research.
Collapse
Affiliation(s)
- Stephen E Harding
- National Centre for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, LE12 5RD, UK.
| | - Richard B Gillis
- National Centre for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, LE12 5RD, UK.,School of Health Sciences, Queen's Medical Centre, Nottingham, NG7 2HA, UK
| | - Gary G Adams
- National Centre for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, LE12 5RD, UK.,School of Health Sciences, Queen's Medical Centre, Nottingham, NG7 2HA, UK
| |
Collapse
|
4
|
Rao A, Cölfen H. Mineralization and non-ideality: on nature's foundry. Biophys Rev 2016; 8:309-329. [PMID: 28510024 DOI: 10.1007/s12551-016-0228-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Accepted: 09/30/2016] [Indexed: 10/20/2022] Open
Abstract
Understanding how ions, ion-clusters and particles behave in non-ideal environments is a fundamental question concerning planetary to atomic scales. For biomineralization phenomena wherein diverse inorganic and organic ingredients are present in biological media, attributing biomaterial composition and structure to the chemistry of singular additives may not provide a holistic view of the underlying mechanisms. Therefore, in this review, we specifically address the consequences of physico-chemical non-ideality on mineral formation. Influences of different forms of non-ideality such as macromolecular crowding, confinement and liquid-like organic phases on mineral nucleation and crystallization in biological environments are presented. Novel prospects for the additive-controlled nucleation and crystallization are accessible from this biophysical view. In this manner, we show that non-ideal conditions significantly affect the form, structure and composition of biogenic and biomimetic minerals.
Collapse
Affiliation(s)
- Ashit Rao
- Freiburg Institute for Advanced Studies, Albert Ludwigs University of Freiburg, 79104, Freiburg im Breisgau, Germany.
| | - Helmut Cölfen
- Physical Chemistry, Department of Chemistry, University of Konstanz, D-78457, Konstanz, Germany.
| |
Collapse
|
5
|
Toogood HS, Leys D, Scrutton NS. Dynamics driving function − new insights from electron transferring flavoproteins and partner complexes. FEBS J 2007; 274:5481-504. [DOI: 10.1111/j.1742-4658.2007.06107.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
6
|
Shi W, Mersfelder J, Hille R. The interaction of trimethylamine dehydrogenase and electron-transferring flavoprotein. J Biol Chem 2005; 280:20239-46. [PMID: 15760891 DOI: 10.1074/jbc.m500582200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The interaction between the physiological electron transfer partners trimethylamine dehydrogenase (TMADH) and electron-transferring flavoprotein (ETF) from Methylophilus methylotrophus has been examined with particular regard to the proposal that the former protein "imprints" a conformational change on the latter. The results indicate that the absorbance change previously attributed to changes in the environment of the FAD of ETF upon binding to TMADH is instead caused by electron transfer from partially reduced, as-isolated TMADH to ETF. Prior treatment of the as-isolated enzyme with the oxidant ferricenium essentially abolishes the observed spectral change. Further, when the semiquinone form of ETF is used instead of the oxidized form, the mirror image of the spectral change seen with as-isolated TMADH and oxidized ETF is observed. This is attributable to a small amount of electron transfer in the reverse of the physiological direction. Kinetic determination of the dissociation constant and limiting rate constant for electron transfer within the complex of (reduced) TMADH with (oxidized) ETF is reconfirmed and discussed in the context of a recently proposed model for the interaction between the two proteins that involves "structural imprinting" of ETF.
Collapse
Affiliation(s)
- Weiwei Shi
- Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, Ohio 43210-1218, USA
| | | | | |
Collapse
|
7
|
Lu X, Nikolic D, Mitchell DJ, van Breemen RB, Mersfelder JA, Hille R, Silverman RB. A mechanism for substrate-Induced formation of 6-hydroxyflavin mononucleotide catalyzed by C30A trimethylamine dehydrogenase. Bioorg Med Chem Lett 2004; 13:4129-32. [PMID: 14592522 DOI: 10.1016/j.bmcl.2003.07.032] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Experiments are described to determine the origin of the 6-hydroxyl group of 6-hydroxyFMN produced by the substrate-induced transformation of FMN in the C30A mutant of trimethylamine dehydrogenase. The conversion of FMN to 6-hydroxyFMN is carried out in the presence of H(2)(18)O and 18O(2), and the results clearly show that the 6-hydroxyl group is derived from molecular oxygen and not from water.
Collapse
Affiliation(s)
- Xingliang Lu
- Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA
| | | | | | | | | | | | | |
Collapse
|
8
|
Hoard-Fruchey HM, Goetzman E, Benson L, Naylor S, Vockley J. Mammalian Electron Transferring Flavoprotein·Flavoprotein Dehydrogenase Complexes Observed by Microelectrospray Ionization-Mass Spectrometry and Surface Plasmon Resonance. J Biol Chem 2004; 279:13786-91. [PMID: 14744856 DOI: 10.1074/jbc.m313914200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Microelectrospray ionization-mass spectrometry was used to directly observe electron transferring flavoprotein.flavoprotein dehydrogenase interactions. When electron transferring flavoprotein and porcine dimethylglycine dehydrogenase or sarcosine dehydrogenase were incubated together in the absence of substrate, a relative molecular mass corresponding to the flavoprotein.electron transferring flavoprotein complex was observed, providing the first direct observation of these mammalian complexes. When an acyl-CoA dehydrogenase family member, human short chain acyl-CoA dehydrogenase, was incubated with dimethylglycine dehydrogenase and electron transferring flavoprotein, the microelectrospray ionization-mass spectrometry signal for the dimethylglycine dehydrogenase.electron transferring flavoprotein complex decreased, indicating that the acyl-CoA dehydrogenases have the ability to compete with the dimethylglycine dehydrogenase/sarcosine dehydrogenase family for access to electron transferring flavoprotein. Surface plasmon resonance solution competition experiments revealed affinity constants of 2.0 and 5.0 microm for the dimethylglycine dehydrogenase-electron transferring flavoprotein and short chain acyl-CoA dehydrogenase-electron transferring flavoprotein interactions, respectively, suggesting the same or closely overlapping binding motif(s) on electron transferring flavoprotein for dehydrogenase interaction.
Collapse
Affiliation(s)
- Heidi M Hoard-Fruchey
- Departments of Biochemistry and Molecular Biology and Medical Genetics, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
| | | | | | | | | |
Collapse
|
9
|
Crowley PB, Carrondo MA. The architecture of the binding site in redox protein complexes: Implications for fast dissociation. Proteins 2004; 55:603-12. [PMID: 15103624 DOI: 10.1002/prot.20043] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Interprotein electron transfer is characterized by protein interactions on the millisecond time scale. Such transient encounters are ensured by extremely high rates of complex dissociation. Computational analysis of the available crystal structures of redox protein complexes reveals features of the binding site that favor fast dissociation. In particular, the complex interface is shown to have low geometric complementarity and poor packing. These features are consistent with the necessity for fast dissociation since the absence of close packing facilitates solvation of the interface and disruption of the complex.
Collapse
Affiliation(s)
- Peter B Crowley
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. Da República, Apartado 127, 2781 901 Oeiras, Portugal.
| | | |
Collapse
|
10
|
Leys D, Basran J, Talfournier F, Sutcliffe MJ, Scrutton NS. Extensive conformational sampling in a ternary electron transfer complex. Nat Struct Mol Biol 2003; 10:219-25. [PMID: 12567183 DOI: 10.1038/nsb894] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2002] [Accepted: 12/19/2002] [Indexed: 11/09/2022]
Abstract
Here we report the crystal structures of a ternary electron transfer complex showing extensive motion at the protein interface. This physiological complex comprises the iron-sulfur flavoprotein trimethylamine dehydrogenase and electron transferring flavoprotein (ETF) from Methylophilus methylotrophus. In addition, we report the crystal structure of free ETF. In the complex, electron density for the FAD domain of ETF is absent, indicating high mobility. Positions for the FAD domain are revealed by molecular dynamics simulation, consistent with crystal structures and kinetic data. A dual interaction of ETF with trimethylamine dehydrogenase provides for dynamical motion at the protein interface: one site acts as an anchor, thereby allowing the other site to sample a large range of interactions, some compatible with rapid electron transfer. This study establishes the role of conformational sampling in multi-domain redox systems, providing insight into electron transfer between ETFs and structurally distinct redox partners.
Collapse
Affiliation(s)
- David Leys
- Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, UK.
| | | | | | | | | |
Collapse
|
11
|
|
12
|
Arkin M, Lear JD. A new data analysis method to determine binding constants of small molecules to proteins using equilibrium analytical ultracentrifugation with absorption optics. Anal Biochem 2001; 299:98-107. [PMID: 11726190 DOI: 10.1006/abio.2001.5396] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In principle, equilibrium analytical ultracentrifugation (AU) can be used to quantify the binding stoichiometry and affinity between small-molecule ligands and proteins in aqueous solution. We show here that heteromeric binding constants can be determined using a data-fitting procedure which utilizes a postfitting computation of the total amount of each component in the centrifuge cell. The method avoids overconstraining the fitting of the radial concentration profiles, but still permits unique binding constants to be determined using measurements at a single wavelength. The computational program is demonstrated by applying it to data obtained with mixtures of a 500-Da molecule and interleukin-2, a 16-kDa protein. The 1:1 binding stoichiometry and heteromeric dissociation constants (K(ab)) determined from centrifuge data at two different wavelengths are within the 4-9 microM range independently determined from a functional assay. Values for K(ab) have been obtained for ligands with affinities as weak as 500 microM. This AU method is applicable to compounds with significant UV absorbance (approximately 0.2) at concentrations within approximately 5- to 10-fold of their K(ab). The method, which has been incorporated into a user procedure for IgorPro (Wavemetrics, Oswego, OR), is included as supplementary material.
Collapse
Affiliation(s)
- M Arkin
- Sunesis Pharmaceuticals Inc., 341 Oyster Point Boulevard, South San Francisco, California 94080, USA
| | | |
Collapse
|
13
|
Scrutton NS, Sutcliffe MJ. Trimethylamine dehydrogenase and electron transferring flavoprotein. Subcell Biochem 2001; 35:145-81. [PMID: 11192721 DOI: 10.1007/0-306-46828-x_5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Affiliation(s)
- N S Scrutton
- Departments of Biochemistry and Chemistry, University of Leicester LE1 7RH, UK
| | | |
Collapse
|
14
|
Chebotareva NA, Harding SE, Winzor DJ. Ultracentrifugal studies of the effect of molecular crowding by trimethylamine N-oxide on the self-association of muscle glycogen phosphorylase b. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:506-13. [PMID: 11168388 DOI: 10.1046/j.1432-1327.2001.01838.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The suitability of sedimentation equilibrium for characterizing the self-association of muscle glycogen phosphorylase b has been reappraised. Whereas sedimentation equilibrium distributions for phosphorylase b in 40 mM Hepes buffer (pH 6.8) supplemented with 1 mM AMP signify a lack of chemical equilibrium attainment, those in buffer supplemented additionally with potassium sulfate conform with the requirements of a dimerizing system in chemical as well as sedimentation equilibrium. Because the rate of attainment of chemical equilibrium under the former conditions is sufficiently slow to allow resolution of the dimeric and tetrameric enzyme species by sedimentation velocity, this procedure has been used to examine the effects of thermodynamic nonideality arising from molecular crowding by trimethylamine N-oxide on the self-association behaviour of phosphorylase b. In those terms the marginally enhanced extent of phosphorylase b self-association observed in the presence of high concentrations of the cosolute is taken to imply that the effects of thermodynamic nonideality on the dimer-tetramer equilibrium are being countered by those displacing the T<==>R isomerization equilibrium for dimer towards the smaller, nonassociating T state. Because the R state is the enzymically active form, an inhibitory effect is the predicted consequence of molecular crowding by high concentrations of unrelated solutes. Thermodynamic nonideality thus provides an alternative explanation for the inhibitory effects of high concentrations of glycerol, sucrose and ethylene glycol on phosphorylase b activity, phenomena that have been attributed to extremely weak interaction of these cryoprotectants with the T state of the enzyme.
Collapse
Affiliation(s)
- N A Chebotareva
- Centre for Macromolecular Hydrodynamics, University of Nottingham, Sutton Bonington, UK
| | | | | |
Collapse
|
15
|
Basran J, Chohan KK, Sutcliffe MJ, Scrutton NS. Differential coupling through Val-344 and Tyr-442 of trimethylamine dehydrogenase in electron transfer reactions with ferricenium ions and electron transferring flavoprotein. Biochemistry 2000; 39:9188-200. [PMID: 10924112 DOI: 10.1021/bi0006868] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Modeling studies of the trimethylamine dehydrogenase-electron transferring flavoprotein (TMADH-ETF) electron transfer complex have suggested potential roles for Val-344 and Tyr-442, found on the surface of TMADH, in electronic coupling between the 4Fe-4S center of TMADH and the FAD of ETF. The importance of these residues in electron transfer, both to ETF and to the artificial electron acceptor, ferricenium (Fc(+)), has been studied by site-directed mutagenesis and stopped-flow spectroscopy. Reduction of the 6-(S)-cysteinyl FMN in TMADH is not affected by mutation of either Tyr-442 or Val-344 to a variety of alternate side chains, although there are modest changes in the rate of internal electron transfer from the 6-(S)-cysteinyl FMN to the 4Fe-4S center. The kinetics of electron transfer from the 4Fe-4S center to Fc(+) are sensitive to mutations at position 344. The introduction of smaller side chains (Ala-344, Cys-344, and Gly-344) leads to enhanced rates of electron transfer, and likely reflects shortened electron transfer "pathways" from the 4Fe-4S center to Fc(+). The introduction of larger side chains (Ile-344 and Tyr-344) reduces substantially the rate of electron transfer to Fc(+). Electron transfer to ETF is not affected, to any large extent, by mutation of Val-344. In contrast, mutation of Tyr-442 to Phe, Leu, Cys, and Gly leads to major reductions in the rate of electron transfer to ETF, but not to Fc(+). The data indicate that electron transfer to Fc(+) is via the shortest pathway from the 4Fe-4S center of TMADH to the surface of the enzyme. Val-344 is located at the end of this pathway at the bottom of a small groove on the surface of TMADH, and Fc(+) can penetrate this groove to facilitate good electronic coupling with the 4Fe-4S center. With ETF as an electron acceptor, the observed rate of electron transfer is substantially reduced on mutation of Tyr-442, but not Val-344. We conclude that the flavin of ETF does not penetrate fully the groove on the surface of TMADH, and that electron transfer from the 4Fe-4S center to ETF may involve a longer pathway involving Tyr-442. Mutation of Tyr-442 likely disrupts electron transfer by perturbing the interaction geometry of TMADH and ETF in the productive electron transfer complex, leading to less efficient coupling between the redox centers.
Collapse
Affiliation(s)
- J Basran
- Department of Biochemistry, University of Leicester, UK
| | | | | | | |
Collapse
|
16
|
Winzor DJ, Jacobsen MP, Wills PR. Direct analysis of sedimentation equilibrium distributions reflecting complex formation between dissimilar reactants. Biochemistry 1998; 37:2226-33. [PMID: 9485368 DOI: 10.1021/bi972211v] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Procedures are developed for the characterization of thermodynamically ideal complex formation between dissimilar macromolecular reactants by direct analysis of sedimentation equilibrium distributions. Studies of an electrostatic interaction between ovalbumin and cytochrome c are used to illustrate the application of analyses pertaining to (i) the situation in which separate sedimentation equilibrium distributions for the two macromolecular constituents are available, (ii) that in which the experimental record reflects the distribution of only one constituent, and (iii) the situation in which a composite distribution for both constituents is the sole experimental record. An association constant of 63 000 (+/- 2000) M-1 is obtained for the 1:1 interaction between ovalbumin and cytochrome c under the conditions examined (pH 6.3, I 0.03). Because of their inherent simplicity, these direct analytical procedures offer potential for accommodating the effects of thermodynamic nonideality in dissimilar reactant systems.
Collapse
Affiliation(s)
- D J Winzor
- Center for Protein Structure, Function and Engineering, Department of Biochemistry, University of Queensland, Brisbane, Queensland 4072, Australia.
| | | | | |
Collapse
|
17
|
Hill CM, Pang SS, Duggleby RG. Purification of Escherichia coli acetohydroxyacid synthase isoenzyme II and reconstitution of active enzyme from its individual pure subunits. Biochem J 1997; 327 ( Pt 3):891-8. [PMID: 9581571 PMCID: PMC1218872 DOI: 10.1042/bj3270891] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The first step in the biosynthesis of branched-chain amino acids is catalysed by acetohydroxyacid synthase (EC 4.1.3.18). The reaction involves the decarboxylation of pyruvate followed by condensation with either a second molecule of pyruvate or with 2-oxobutyrate. The enzyme requires as cofactors thiamine diphosphate, a divalent metal ion and, usually, FAD. In most bacteria the enzyme is a heterotetramer of two large and two small subunits. Escherichia coli contains three active isoenzymes and the present study concerns isoenzyme II, whose large and small subunits are encoded by the ilvG and ilvM genes respectively. Cloning these genes into a plasmid vector and overexpression in E. coli allowed a two-step purification procedure for the native enzyme to be developed. The level of expression is considerably higher from a vector that introduces a 50 residue N-terminal fusion containing an oligohistidine sequence on the large subunit. Purification to homogeneity was achieved in a single step by immobilized-metal-affinity chromatography. The kinetic properties of the native and fusion enzyme are indistinguishable with respect to the substrate pyruvate and the inhibitor chlorsulfuron. The individual subunits were expressed as oligohistidine-tagged fusion proteins and each was purified in a single step. Neither subunit alone has significant enzymic activity but, on mixing, the enzyme is reconstituted. The kinetic properties of the reconstituted enzyme are very similar to those of the fusion enzyme. It is proposed that the reconstitution pathway involves successive, and highly co-operative, binding of two small subunit monomers to a large subunit dimer. None of the cofactors is needed for subunit association although they are necessary for the restoration of enzymic activity.
Collapse
Affiliation(s)
- C M Hill
- Centre for Protein Structure, Function and Engineering, Department of Biochemistry, University of Queensland, Brisbane 4072, Australia
| | | | | |
Collapse
|
18
|
Mewies M, Basran J, Packman LC, Hille R, Scrutton NS. Involvement of a flavin iminoquinone methide in the formation of 6-hydroxyflavin mononucleotide in trimethylamine dehydrogenase: a rationale for the existence of 8alpha-methyl and C6-linked covalent flavoproteins. Biochemistry 1997; 36:7162-8. [PMID: 9188716 DOI: 10.1021/bi970621d] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In trimethylamine dehydrogenase, substrate is bound in the active site via cation-pi bonding to three aromatic residues (Tyr-60, Trp-264, and Trp-355). Mutation of one of these residues (Trp-355 --> Leu, mutant W355L) influences the chemistry of the flavin mononucleotide in the active site, enabling derivatization to 6-hydroxy-FMN. The W355L mutant is purified as a mixture of deflavo, natural 6-S-cysteinyl-FMN, and inactive 6-hydroxy-FMN forms, and the enzyme is severely compromised in its ability to oxidatively demethylate trimethylamine. Analysis of samples of the native and recombinant wild-type trimethylamine dehydrogenases also revealed the presence of 6-hydroxy-FMN, but at much reduced levels compared with that of the W355L enzyme. Unlike that for a C30A mutant of trimethylamine dehydrogenase, addition of substrate to the W355L trimethylamine dehydrogenase is not required for the production of 6-hydroxy-FMN. A mechanism is proposed for the 6-hydroxylation of FMN in trimethylamine dehydrogenase that involves an electrophilic flavin iminoquinone methide. The proposed mechanism involving the flavin iminoquinone methide could apply to the flavinylation of trimethylamine dehydrogenase at the C6 position but also to the flavinylation of enzymes via the 8alpha position, thus providing a rationale for the evolution of covalent flavoproteins in general. Covalent linkage at C6 or the 8alpha-methyl prevents 6-hydroxylation by direct modification at the C6 atom or by preventing formation of the flavin iminoquinone methide, respectively.
Collapse
Affiliation(s)
- M Mewies
- Department of Biochemistry, University of Leicester, U.K
| | | | | | | | | |
Collapse
|