scholarly journals The structure of the quinoprotein alcohol dehydrogenase of Acetobacter aceti modelled on that of methanol dehydrogenase from Methylobacterium extorquens

1995 ◽  
Vol 308 (2) ◽  
pp. 375-379 ◽  
Author(s):  
G E Cozier ◽  
I G Giles ◽  
C Anthony
Keyword(s):  
Alcohol Dehydrogenase ◽  
Active Site ◽  
Mechanisms Of Action ◽  
Methanol Dehydrogenase ◽  
Model Structure ◽  
Methylobacterium Extorquens ◽  
Acetobacter Aceti ◽  
Active Site Region

The 1.94 A structure of methanol dehydrogenase has been used to provide a model structure for part of a membrane quinohaemoprotein alcohol dehydrogenase. The basic superbarrel structure and the active-site region are retained, indicating essentially similar mechanisms of action, but there are considerable differences in the external loops, particularly those involved in formation of the shallow funnel leading to the active site.

scholarly journals Structure of the quinoprotein glucose dehydrogenase of Escherichia coli modelled on that of methanol dehydrogenase from Methylobacterium extorquens

1995 ◽  
Vol 312 (3) ◽  
pp. 679-685 ◽  
Author(s):  
G E Cozier ◽  
C Anthony
Keyword(s):  
Active Site ◽  
Glucose Dehydrogenase ◽  
Ring Structure ◽  
Enzymic Activity ◽  
Methanol Dehydrogenase ◽  
The Novel ◽  
Methylobacterium Extorquens ◽  
Prosthetic Group ◽  
Site Structure ◽  
Proposed Model

The structure of methanol dehydrogenase (MDH) at 0.194 nm (1.94 A) has been used to provide a model structure for part of a membrane quinoprotein glucose dehydrogenase (GDH). The basic superbarrel structure is retained, along with the tryptophan-docking motifs. The active-site regions are similar, but there are important differences, the most important being that GDH lacks the novel disulphide ring structure formed from adjacent cysteines in MDH; in GDH the equivalent region is occupied by His-262. Because of the overall similarities in the active-site region, the mechanism of action of GDH is likely to be similar to that of MDH. The differences in co-ordination to the cation and bonding to the pyrrolo-quinoline quinone (PQQ) in the active site may explain the relative ease of dissociation of the prosthetic group from the holo-GDH. There are considerable differences in the external loops, particularly those involved in formation of the shallow funnel leading to the active site, the configuration of which influences substrate specificity. The proposed model is consistent in many respects with previous proposals for the active-site structure based on the effects of chemical modification on binding of PQQ and enzymic activity.

scholarly journals The role of the novel disulphide ring in the active site of the quinoprotein methanol dehydrogenase from Methylobacterium extorquens

1995 ◽  
Vol 307 (3) ◽  
pp. 735-741 ◽  
Author(s):  
A Avezoux ◽  
M G Goodwin ◽  
C Anthony
Keyword(s):  
Active Site ◽  
Hydrogen Transfer ◽  
Ring Structure ◽  
Methanol Dehydrogenase ◽  
Active Enzyme ◽  
The Novel ◽  
Methylobacterium Extorquens ◽  
Disulphide Bridge ◽  
Prosthetic Group ◽  
Cytochrome Cl

All cysteines in methanol dehydrogenase (MDH) from Methylobacterium extorquens are involved in intra-subunit disulphide bridge formation. One of these is between adjacent cysteine residues which form a novel ring structure in the active site. It is readily reduced, the reduced enzyme being inactive in electron transfer to cytochrome cL. The inactivation is not a result of major structural change or to modification of the prosthetic group pyrrolo-quinoline quinone (PQQ). The reduced enzyme appears to remain active with the artificial electron acceptor phenazine ethosulphate but this is because the dye re-oxidizes the adjacent thiols back to the original disulphide bridge. No free thiols were detected during the reaction cycle with cytochrome cL. Carboxymethylation of the thiols produced by reduction of the novel disulphide ring led to formation of active enzyme. Reconstitution of inactive Ca(2+)-free MDH with Ca2+ led to active enzyme containing the oxidized bridge and reduced quinol, PQQH2, consistent with the conclusion that no hydrogen transfer occurs between these groups in the active site. It is concluded that the disulphide ring in the active site of MDH does not function as a redox component of the reaction. The disulphide ring has no special function in the process of Ca2+ incorporation into the active site. It is suggested that this novel structure might function in the stabilization or protection of the free radical semiquinone form of the prosthetic group (PQQH.) from solvent at the entrance to the active site.

scholarly journals Activity of linked HIV-1 proteinase dimers containing mutations in the active site region

1996 ◽  
Vol 9 (11) ◽  
pp. 997-1003 ◽  
Author(s):  
Péter Bagossi ◽  
Yin-Shyun E. Cheng ◽  
Stephen Oroszlan ◽  
József Tözsér
Keyword(s):  
Active Site ◽  
Active Site Region ◽  
Hiv 1

scholarly journals A crystallographic study of the Toho-1 β-lactamase acylation mechanism

2014 ◽  
Vol 70 (a1) ◽  
pp. C1207-C1207
Author(s):  
Leighton Coates
Keyword(s):  
Hydrogen Bonding ◽  
Transition State ◽  
Active Site ◽  
Catalytic Mechanism ◽  
Substrate Binding ◽  
Ligand Complex ◽  
Transition State Analog ◽  
Hydrogen Bonding Interactions ◽  
Active Site Region ◽  
Neutron Crystallography

β-lactam antibiotics have been used effectively over several decades against many types of highly virulent bacteria. The predominant cause of resistance to these antibiotics in Gram-negative bacterial pathogens is the production of serine β-lactamase enzymes. A key aspect of the class A serine β-lactamase mechanism that remains unresolved and controversial is the identity of the residue acting as the catalytic base during the acylation reaction. Multiple mechanisms have been proposed for the formation of the acyl-enzyme intermediate that are predicated on understanding the protonation states and hydrogen-bonding interactions among the important residues involved in substrate binding and catalysis of these enzymes. For resolving a controversy of this nature surrounding the catalytic mechanism, neutron crystallography is a powerful complement to X-ray crystallography that can explicitly determine the location of deuterium atoms in proteins, thereby directly revealing the hydrogen-bonding interactions of important amino acid residues. Neutron crystallography was used to unambiguously reveal the ground-state active site protonation states and the resulting hydrogen-bonding network in two ligand-free Toho-1 β-lactamase mutants which provided remarkably clear pictures of the active site region prior to substrate binding and subsequent acylation [1,2] and an acylation transition-state analog, benzothiophene-2-boronic acid (BZB), which was also isotopically enriched with 11B. The neutron structure revealed the locations of all deuterium atoms in the active site region and clearly indicated that Glu166 is protonated in the BZB transition-state analog complex. As a result, the complete hydrogen-bonding pathway throughout the active site region could then deduced for this protein-ligand complex that mimics the acylation tetrahedral intermediate [3].

scholarly journals Digital dissection of arsenate reductase enzyme from an arsenic hyperccumulating fern Pteris vittata

2016 ◽  
Author(s):  
Zarrin Basharat ◽  
Deeba Noreen Baig ◽  
Azra Yasmin
Keyword(s):  
Neural Network ◽  
Active Site ◽  
Tertiary Structure ◽  
Pteris Vittata ◽  
Arsenate Reductase ◽  
Dynamics Simulation ◽  
Reduction Mechanism ◽  
Arsenic Reduction ◽  
Secondary And Tertiary Structure ◽  
Active Site Region

Action of arsenate reductase is crucial for the survival of an organism in arsenic polluted area. Pteris vittata, also known as Chinese ladder brake, was the first identified arsenic hyperaccumulating fern with the capability to convert [As(V)] to arsenite [As(III)]. This study aims at sequence analysis of the most important protein of the arsenic reduction mechanism in this specie. Phosphorylation potential of the protein along with possible interplay of phosphorylation with O-β-GlcNAcylation was predicted using neural network based webservers. Secondary and tertiary structure of arsenate reductase was then analysed. Active site region of the protein comprised a rhodanese-like domain. Cursory dynamics simulation revealed that folds remained conserved in the rhodanese main but variations were observed in the structure in other regions. This information sheds light on the various characteristics of the protein and may be useful to enzymologists working on the improvement of its traits for arsenic reduction.

scholarly journals Functional investigation of methanol dehydrogenase-like protein XoxF in Methylobacterium extorquens AM1

Microbiology ◽  
2010 ◽  
Vol 156 (8) ◽  
pp. 2575-2586 ◽  
Author(s):  
Sabrina Schmidt ◽  
Philipp Christen ◽  
Patrick Kiefer ◽  
Julia A. Vorholt
Keyword(s):  
Growth Parameters ◽  
Methanol Dehydrogenase ◽  
Plant Colonization ◽  
Kinetic Properties ◽  
Wild Type ◽  
Methylobacterium Extorquens ◽  
Experimental Conditions ◽  
Dependent Protein ◽  
One Carbon Metabolism ◽  
Functional Investigation

Methanol dehydrogenase-like protein XoxF of Methylobacterium extorquens AM1 exhibits a sequence identity of 50 % to the catalytic subunit MxaF of periplasmic methanol dehydrogenase in the same organism. The latter has been characterized in detail, identified as a pyrroloquinoline quinone (PQQ)-dependent protein, and shown to be essential for growth in the presence of methanol in this methylotrophic model bacterium. In contrast, the function of XoxF in M. extorquens AM1 has not yet been elucidated, and a phenotype remained to be described for a xoxF mutant. Here, we found that a xoxF mutant is less competitive than the wild-type during colonization of the phyllosphere of Arabidopsis thaliana, indicating a function for XoxF during plant colonization. A comparison of the growth parameters of the M. extorquens AM1 xoxF mutant with those of the wild-type during exponential growth revealed a reduced methanol uptake rate and a reduced growth rate for the xoxF mutant of about 30 %. Experiments with cells starved for carbon revealed that methanol oxidation in the xoxF mutant occurs less rapidly compared with the wild-type, especially in the first minutes after methanol addition. A distinct phenotype for the xoxF mutant was also observed when formate and CO2 production were measured after the addition of methanol or formaldehyde to starved cells. The wild-type, but not the xoxF mutant, accumulated formate upon substrate addition and had a 1 h lag in CO2 production under the experimental conditions. Determination of the kinetic properties of the purified enzyme showed a conversion capacity for both formaldehyde and methanol. The results suggest that XoxF is involved in one-carbon metabolism in M. extorquens AM1.

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