1
|
Hulen C. The GDP-Mannose Dehydrogenase of Pseudomonas aeruginosa: An Old and New Target to Fight against Antibiotics Resistance of Mucoid Strains. Antibiotics (Basel) 2023; 12:1649. [PMID: 38136683 PMCID: PMC10740432 DOI: 10.3390/antibiotics12121649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Revised: 11/06/2023] [Accepted: 11/07/2023] [Indexed: 12/24/2023] Open
Abstract
Alginates play an important role in the resistance of mucoid strains of Pseudomonas aeruginosa to antibiotics, as well as their persistence by escaping the immune defense system. GDP-mannose dehydrogenase (GMD) is the key enzyme in alginate biosynthesis by catalyzing the irreversible double oxidation of GDP-mannose to GDP-mannuronate. GDP-mannose dehydrogenase purified from mucoid strains exhibits strong negative cooperativity for its substrate, the GDP-mannose, with a KM of 13 µM for the site of strong affinity and 3 mM for this weak of a binding. The presence of a nucleotide strongly associated with the enzyme was detected, confirming the fact that the substrate oxidation reaction takes place in two distinct steps, with the substrate blocked on the enzyme in a half-oxidation state in the form of a hemiacetal. As the GMD polypeptide has only one site for substrate binding, our results tend to confirm the fact that the enzyme functions in a dimer form. The GDP-mannose dehydrogenase inhibition strategy that we developed a few years ago, based on the synthesis of substrate analogs, has shown its effectiveness. The addition of an alkynyl radical on carbon 6 of the mannose grafted to an amino-sulfonyl-guanosine allows, at a concentration of 0.5 mM, to inhibit GMD by 90%. As we had previously shown the effectiveness of these analogs on the sensitivity of mucoid strains of Pseudomonas aeruginosa to aminoglycosides, this revives the interest in the synthesis of new inhibitors of GDP-mannose dehydrogenase.
Collapse
Affiliation(s)
- Christian Hulen
- Bacterial Communication and Antimicrobial Strategies Research Unit, University of Rouen Normandy, 55 Rue Saint Germain, 27000 Evreux, France
| |
Collapse
|
2
|
Viral community analysis in a marine oxygen minimum zone indicates increased potential for viral manipulation of microbial physiological state. THE ISME JOURNAL 2022; 16:972-982. [PMID: 34743175 PMCID: PMC8940887 DOI: 10.1038/s41396-021-01143-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 10/11/2021] [Accepted: 10/13/2021] [Indexed: 11/08/2022]
Abstract
Microbial communities in oxygen minimum zones (OMZs) are known to have significant impacts on global biogeochemical cycles, but viral influence on microbial processes in these regions are much less studied. Here we provide baseline ecological patterns using microscopy and viral metagenomics from the Eastern Tropical North Pacific (ETNP) OMZ region that enhance our understanding of viruses in these climate-critical systems. While extracellular viral abundance decreased below the oxycline, viral diversity and lytic infection frequency remained high within the OMZ, demonstrating that viral influences on microbial communities were still substantial without the detectable presence of oxygen. Viral community composition was strongly related to oxygen concentration, with viral populations in low-oxygen portions of the water column being distinct from their surface layer counterparts. However, this divergence was not accompanied by the expected differences in viral-encoded auxiliary metabolic genes (AMGs) relating to nitrogen and sulfur metabolisms that are known to be performed by microbial communities in these low-oxygen and anoxic regions. Instead, several abundant AMGs were identified in the oxycline and OMZ that may modulate host responses to low-oxygen stress. We hypothesize that this is due to selection for viral-encoded genes that influence host survivability rather than modulating host metabolic reactions within the ETNP OMZ. Together, this study shows that viruses are not only diverse throughout the water column in the ETNP, including the OMZ, but their infection of microorganisms has the potential to alter host physiological state within these biogeochemically important regions of the ocean.
Collapse
|
3
|
Gheorghita AA, Wolfram F, Whitfield GB, Jacobs HM, Pfoh R, Wong SSY, Guitor AK, Goodyear MC, Berezuk AM, Khursigara CM, Parsek MR, Howell PL. The Pseudomonas aeruginosa homeostasis enzyme AlgL clears the periplasmic space of accumulated alginate during polymer biosynthesis. J Biol Chem 2022; 298:101560. [PMID: 34990713 PMCID: PMC8829089 DOI: 10.1016/j.jbc.2021.101560] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 12/27/2021] [Accepted: 12/28/2021] [Indexed: 11/24/2022] Open
Abstract
Pseudomonas aeruginosa is an opportunistic human pathogen and a leading cause of chronic infection in the lungs of individuals with cystic fibrosis. After colonization, P. aeruginosa often undergoes a phenotypic conversion to mucoidy, characterized by overproduction of the alginate exopolysaccharide. This conversion is correlated with poorer patient prognoses. The majority of genes required for alginate synthesis, including the alginate lyase, algL, are located in a single operon. Previous investigations of AlgL have resulted in several divergent hypotheses regarding the protein’s role in alginate production. To address these discrepancies, we determined the structure of AlgL and, using multiple sequence alignments, identified key active site residues involved in alginate binding and catalysis. In vitro enzymatic analysis of active site mutants highlights R249 and Y256 as key residues required for alginate lyase activity. In a genetically engineered P. aeruginosa strain where alginate biosynthesis is under arabinose control, we found that AlgL is required for cell viability and maintaining membrane integrity during alginate production. We demonstrate that AlgL functions as a homeostasis enzyme to clear the periplasmic space of accumulated polymer. Constitutive expression of the AlgU/T sigma factor mitigates the effects of an algL deletion during alginate production, suggesting that an AlgU/T-regulated protein or proteins can compensate for an algL deletion. Together, our study demonstrates the role of AlgL in alginate biosynthesis, explains the discrepancies observed previously across other P. aeruginosa ΔalgL genetic backgrounds, and clarifies the existing divergent data regarding the function of AlgL as an alginate degrading enzyme.
Collapse
Affiliation(s)
- Andreea A Gheorghita
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Francis Wolfram
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Gregory B Whitfield
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Holly M Jacobs
- Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, Washington, USA
| | - Roland Pfoh
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Steven S Y Wong
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Allison K Guitor
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Mara C Goodyear
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Alison M Berezuk
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Cezar M Khursigara
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Matthew R Parsek
- Department of Microbiology, University of Washington, Seattle, Washington, USA
| | - P Lynne Howell
- Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
| |
Collapse
|
4
|
Beswick L, Dimitriou E, Ahmadipour S, Zafar A, Rejzek M, Reynisson J, Field RA, Miller GJ. Inhibition of the GDP-d-Mannose Dehydrogenase from Pseudomonas aeruginosa Using Targeted Sugar Nucleotide Probes. ACS Chem Biol 2020; 15:3086-3092. [PMID: 33237714 DOI: 10.1021/acschembio.0c00426] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Sufferers of cystic fibrosis are at extremely high risk for contracting chronic lung infections. Over their lifetime, one bacterial strain in particular, Pseudomonas aeruginosa, becomes the dominant pathogen. Bacterial strains incur loss-of-function mutations in the mucA gene that lead to a mucoid conversion, resulting in copious secretion of the exopolysaccharide alginate. Strategies that stop the production of alginate in mucoid Pseudomonas aeruginosa infections are therefore of paramount importance. To aid in this, a series of sugar nucleotide tools to probe an enzyme critical to alginate biosynthesis, guanosine diphosphate mannose dehydrogenase (GMD), have been developed. GMD catalyzes the irreversible formation of the alginate building block, guanosine diphosphate mannuronic acid. Using a chemoenzymatic strategy, we accessed a series of modified sugar nucleotides, identifying a C6-amide derivative of guanosine diphosphate mannose as a micromolar inhibitor of GMD. This discovery provides a framework for wider inhibition strategies against GMD to be developed.
Collapse
Affiliation(s)
- Laura Beswick
- Lennard-Jones Laboratory, School of Chemical and Physical Sciences, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| | - Eleni Dimitriou
- Lennard-Jones Laboratory, School of Chemical and Physical Sciences, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| | - Sanaz Ahmadipour
- Department of Chemistry and Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Ayesha Zafar
- School of Chemical Sciences, University of Auckland, 23 Symonds Street, 1142 Auckland, New Zealand
| | - Martin Rejzek
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, United Kingdom
| | - Jóhannes Reynisson
- Hornbeam Building, School of Pharmacy and Bioengineering, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| | - Robert A Field
- Department of Chemistry and Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Gavin J Miller
- Lennard-Jones Laboratory, School of Chemical and Physical Sciences, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| |
Collapse
|
5
|
Catalytic mechanism of UDP-glucose dehydrogenase. Biochem Soc Trans 2019; 47:945-955. [PMID: 31189734 DOI: 10.1042/bst20190257] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 05/15/2019] [Accepted: 05/21/2019] [Indexed: 11/17/2022]
Abstract
UDP-glucose dehydrogenase (UGDH), an oxidoreductase, catalyzes the NAD+-dependent four-electron oxidation of UDP-glucose to UDP-glucuronic acid. The catalytic mechanism of UGDH remains controversial despite extensive investigation and is classified into two types according to whether an aldehyde intermediate is generated in the first oxidation step. The first type, which involves the presence of this putative aldehyde, is inconsistent with some experimental findings. In contrast, the second type, which indicates that the first oxidation step bypasses the aldehyde via an NAD+-dependent bimolecular nucleophilic substitution (SN2) reaction, is consistent with the experimental phenomena, including those that cannot be explained by the first type. This NAD+-dependent SN2 mechanism is thus more reasonable and likely applicable to other oxidoreductases that catalyze four-electron oxidation reactions.
Collapse
|
6
|
A hyaluronan-based polysaccharide peptide generated by a genetically modified Streptococcus zooepidemicus. Carbohydr Res 2019; 478:25-32. [DOI: 10.1016/j.carres.2019.04.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 04/01/2019] [Accepted: 04/18/2019] [Indexed: 01/08/2023]
|
7
|
Chen J, Yu Y, Gao J, Yang S. UDP-glucose Dehydrogenase: The First-step Oxidation Is an NAD +-dependent Bimolecular Nucleophilic Substitution Reaction (S N2). Int J Biol Sci 2019; 15:341-350. [PMID: 30745825 PMCID: PMC6367545 DOI: 10.7150/ijbs.28904] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 11/11/2018] [Indexed: 11/05/2022] Open
Abstract
UDP-glucose dehydrogenase (UGDH) catalyzes the conversion of UDP-glucose to UDP-glucuronic acid by NAD+-dependent two-fold oxidation. Despite extensive investigation into the catalytic mechanism of UGDH, the previously proposed mechanisms regarding the first-step oxidation are somewhat controversial and inconsistent with some biochemical evidence, which instead supports a mechanism involving an NAD+-dependent bimolecular nucleophilic substitution (SN2) reaction. To verify this speculation, the essential Cys residue of Streptococcus zooepidemicus UGDH (SzUGDH) was changed to an Ala residue, and the resulting Cys260Ala mutant and SzUGDH were then co-expressed in vivo via a single-crossover homologous recombination method. Contrary to the previously proposed mechanisms, which predict the formation of the capsular polysaccharide hyaluronan, the resulting strain instead produced an amide derivative of hyaluronan, as validated via proteinase K digestion, ninhydrin reaction, FT-IR and NMR. This result is compatible with the NAD+-dependent SN2 mechanism.
Collapse
Affiliation(s)
- Jun Chen
- School of Environmental & Biological Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, China, 210094
| | - Yang Yu
- School of Environmental & Biological Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, China, 210094
| | - Jiaojiao Gao
- School of Environmental & Biological Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, China, 210094
| | - Shulin Yang
- School of Environmental & Biological Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, China, 210094
| |
Collapse
|
8
|
Grady G, Thelen A, Albers J, Ju T, Guo J, Barycki JJ, Simpson MA. Inhibiting Hexamer Disassembly of Human UDP-Glucose Dehydrogenase by Photoactivated Amino Acid Cross-Linking. Biochemistry 2016; 55:3157-64. [PMID: 27198584 DOI: 10.1021/acs.biochem.6b00259] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The enzyme UDP-glucose dehydrogenase (UGDH) catalyzes the reaction of UDP-glucose to UDP-glucuronate through two successive NAD(+)-dependent oxidation steps. Human UGDH apoprotein is purified as a mixture of dimeric and hexameric species. Addition of substrate and cofactor stabilizes the oligomeric state to primarily the hexameric form. To determine if the dynamic conformations of hUGDH are required for catalytic activity, we used site-specific unnatural amino acid incorporation to facilitate cross-linking of monomeric subunits into predominantly obligate oligomeric species. Optimal cross-linking was achieved by encoding p-benzoyl-l-phenylalanine at position 458, normally a glutamine located within the dimer-dimer interface, and exposing the enzyme to long wavelength ultraviolet (UV) radiation in the presence of substrate and cofactor. Hexameric complexes were purified by gel filtration chromatography and found to contain significant fractions of dimer and trimer (approximately 50%) along with another 10% higher-molecular mass species. The activity of the cross-linked enzyme was reduced by almost 60% relative to that of the un-cross-linked UGDH mutant, and UV exposure had no effect on the activity of the wild-type enzyme. These results support a model for catalysis in which the ability to dissociate the dimer-dimer interface is as important for maximal enzyme function as has been previously shown for the formation of the hexamer.
Collapse
Affiliation(s)
- George Grady
- Department of Biochemistry, University of Nebraska , Lincoln, Nebraska 68588-0664, United States
| | - Ashley Thelen
- Department of Biochemistry, University of Nebraska , Lincoln, Nebraska 68588-0664, United States
| | - Jaleen Albers
- Department of Biochemistry, University of Nebraska , Lincoln, Nebraska 68588-0664, United States
| | - Tong Ju
- Department of Chemistry, University of Nebraska , Lincoln, Nebraska 68588-0304, United States
| | - Jiantao Guo
- Department of Chemistry, University of Nebraska , Lincoln, Nebraska 68588-0304, United States
| | - Joseph J Barycki
- Department of Biochemistry, University of Nebraska , Lincoln, Nebraska 68588-0664, United States
| | - Melanie A Simpson
- Department of Biochemistry, University of Nebraska , Lincoln, Nebraska 68588-0664, United States
| |
Collapse
|
9
|
Molecular mechanism and evolution of guanylate kinase regulation by (p)ppGpp. Mol Cell 2015; 57:735-749. [PMID: 25661490 PMCID: PMC4336630 DOI: 10.1016/j.molcel.2014.12.037] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Revised: 11/07/2014] [Accepted: 12/22/2014] [Indexed: 01/07/2023]
Abstract
The nucleotide (p)ppGpp mediates bacterial stress responses, but its targets and underlying mechanisms of action vary among bacterial species and remain incompletely understood. Here, we characterize the molecular interaction between (p)ppGpp and guanylate kinase (GMK), revealing the importance of this interaction in adaptation to starvation. Combining structural and kinetic analyses, we show that (p)ppGpp binds the GMK active site and competitively inhibits the enzyme. The (p)ppGpp-GMK interaction prevents the conversion of GMP to GDP, resulting in GMP accumulation upon amino acid downshift. Abolishing this interaction leads to excess (p)ppGpp and defective adaptation to amino acid starvation. A survey of GMKs from phylogenetically diverse bacteria shows that the (p)ppGpp-GMK interaction is conserved in members of Firmicutes, Actinobacteria, and Deinococcus-Thermus, but not in Proteobacteria, where (p)ppGpp regulates RNA polymerase (RNAP). We propose that GMK is an ancestral (p)ppGpp target and RNAP evolved more recently as a direct target in Proteobacteria.
Collapse
|
10
|
Su JQ, Wei B, Xu CY, Qiao M, Zhu YG. Functional metagenomic characterization of antibiotic resistance genes in agricultural soils from China. ENVIRONMENT INTERNATIONAL 2014; 65:9-15. [PMID: 24412260 DOI: 10.1016/j.envint.2013.12.010] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 09/13/2013] [Accepted: 12/13/2013] [Indexed: 05/12/2023]
Abstract
Soil has been regarded as a rich source of antibiotic resistance genes (ARGs) due to the complex microbial community and diverse antibiotic-producing microbes in soil, however, little is known about the ARGs in unculturable bacteria. To investigate the diversity and distribution of ARGs in soil and assess the impact of agricultural practice on the ARGs, we screened soil metagenomic library constructed using DNA from four different agricultural soil for ARGs. We identified 45 clones conferring resistance to minocycline, tetracycline, streptomycin, gentamicin, kanamycin, amikacin, chloramphenicol and rifampicin. The similarity of identified ARGs with the closest protein in GenBank ranged from 26% to 92%, with more than 60% of identified ARGs had low similarity less than 60% at amino acid level. The identified ARGs include aminoglycoside acetyltransferase, aminoglycoside 6-adenyltransferase, ADP-ribosyl transferase, ribosome protection protein, transporters and other antibiotic resistant determinants. The identified ARGs from the soil with manure application account for approximately 70% of the total ARGs in this study, implying that manure amendment may increase the diversity of antibiotic resistance genes in soil bacteria. These results suggest that antibiotic resistance in soil remains unexplored and functional metagenomic approach is powerful in discovering novel ARGs and resistant mechanisms.
Collapse
Affiliation(s)
- Jian Qiang Su
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
| | - Bei Wei
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
| | - Chun Yan Xu
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
| | - Min Qiao
- State Key Lab of Urban and Regional Ecology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yong Guan Zhu
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China; State Key Lab of Urban and Regional Ecology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
| |
Collapse
|
11
|
Farrell EK, Tipton PA. Functional characterization of AlgL, an alginate lyase from Pseudomonas aeruginosa. Biochemistry 2012; 51:10259-66. [PMID: 23215237 DOI: 10.1021/bi301425r] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Alginate lyase (AlgL) catalyzes the cleavage of the polysaccharide alginate through a β-elimination reaction. In Pseudomonas aeruginosa, algL is part of the alginate biosynthetic operon, and although it is required for alginate biosynthesis, it is not clear why. Steady-state kinetic studies were performed to characterize its substrate specificity and revealed that AlgL operates preferentially on nonacetylated alginate or its precursor mannuronan. Mature alginate is secreted as a partially acetylated polysaccharide, so this observation is consistent with suggestions that AlgL serves to degrade mislocalized alginate that is trapped in the periplasmic space. The k(cat)/K(m) for the reaction increased linearly with the number of residues in the substrate, from 2.1 × 10(5) M(-1) s(-1) for the substrate containing 16 residues to 7.9 × 10(6) M(-1) s(-1) for the substrate with 280 residues. Over the same substrate size range, k(cat) varied between 10 and 30 s(-1). The variation in k(cat)/K(m) with substrate length suggests that AlgL operates in a processive manner. AlgL displayed a surprising lack of stereospecificity, in that it was able to catalyze cleavage adjacent to either mannuronate or guluronate residues in alginate. Thus, the enzyme is able to remove the C5 proton from both mannuronate and guluronate, which are C5 epimers. Exhaustive digestion of alginate by AlgL generated dimeric and trimeric products, which were characterized by (1)H nuclear magnetic resonance spectroscopy and mass spectrometry. Rapid-mixing chemical quench studies revealed that there was no lag in dimer or trimer production, indicating that AlgL operates as an exopolysaccharide lyase.
Collapse
Affiliation(s)
- Emma K Farrell
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | | |
Collapse
|
12
|
Hyde AS, Farmer EL, Easley KE, van Lammeren K, Christoffels VM, Barycki JJ, Bakkers J, Simpson MA. UDP-glucose dehydrogenase polymorphisms from patients with congenital heart valve defects disrupt enzyme stability and quaternary assembly. J Biol Chem 2012; 287:32708-16. [PMID: 22815472 DOI: 10.1074/jbc.m112.395202] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Cardiac valve defects are a common congenital heart malformation and a significant clinical problem. Defining molecular factors in cardiac valve development has facilitated identification of underlying causes of valve malformation. Gene disruption in zebrafish revealed a critical role for UDP-glucose dehydrogenase (UGDH) in valve development, so this gene was screened for polymorphisms in a patient population suffering from cardiac valve defects. Two genetic substitutions were identified and predicted to encode missense mutations of arginine 141 to cysteine and glutamate 416 to aspartate, respectively. Using a zebrafish model of defective heart valve formation caused by morpholino oligonucleotide knockdown of UGDH, transcripts encoding the UGDH R141C or E416D mutant enzymes were unable to restore cardiac valve formation and could only partially rescue cardiac edema. Characterization of the mutant recombinant enzymes purified from Escherichia coli revealed modest alterations in the enzymatic activity of the mutants and a significant reduction in the half-life of enzyme activity at 37 °C. This reduction in activity could be propagated to the wild-type enzyme in a 1:1 mixed reaction. Furthermore, the quaternary structure of both mutants, normally hexameric, was destabilized to favor the dimeric species, and the intrinsic thermal stability of the R141C mutant was highly compromised. The results are consistent with the reduced function of both missense mutations significantly reducing the ability of UGDH to provide precursors for cardiac cushion formation, which is essential to subsequent valve formation. The identification of these polymorphisms in patient populations will help identify families genetically at risk for valve defects.
Collapse
Affiliation(s)
- Annastasia S Hyde
- Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588-0664, USA
| | | | | | | | | | | | | | | |
Collapse
|
13
|
Selwood T, Jaffe EK. Dynamic dissociating homo-oligomers and the control of protein function. Arch Biochem Biophys 2012; 519:131-43. [PMID: 22182754 PMCID: PMC3298769 DOI: 10.1016/j.abb.2011.11.020] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Revised: 11/16/2011] [Accepted: 11/28/2011] [Indexed: 11/20/2022]
Abstract
Homo-oligomeric protein assemblies are known to participate in dynamic association/disassociation equilibria under native conditions, thus creating an equilibrium of assembly states. Such quaternary structure equilibria may be influenced in a physiologically significant manner either by covalent modification or by the non-covalent binding of ligands. This review follows the evolution of ideas about homo-oligomeric equilibria through the 20th and into the 21st centuries and the relationship of these equilibria to allosteric regulation by the non-covalent binding of ligands. A dynamic quaternary structure equilibria is described where the dissociated state can have alternate conformations that cannot reassociate to the original multimer; the alternate conformations dictate assembly to functionally distinct alternate multimers of finite stoichiometry. The functional distinction between different assemblies provides a mechanism for allostery. The requirement for dissociation distinguishes this morpheein model of allosteric regulation from the classical MWC concerted and KNF sequential models. These models are described alongside earlier dissociating allosteric models. The identification of proteins that exist as an equilibrium of diverse native quaternary structure assemblies has the potential to define new targets for allosteric modulation with significant consequences for further understanding and/or controlling protein structure and function. Thus, a rationale for identifying proteins that may use the morpheein model of allostery is presented and a selection of proteins for which published data suggests this mechanism may be operative are listed.
Collapse
Affiliation(s)
- Trevor Selwood
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA, 19111
| | - Eileen K. Jaffe
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA, 19111
| |
Collapse
|
14
|
Jaffe EK, Lawrence SH. The morpheein model of allostery: evaluating proteins as potential morpheeins. Methods Mol Biol 2012; 796:217-31. [PMID: 22052493 PMCID: PMC3256758 DOI: 10.1007/978-1-61779-334-9_12] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
Abstract
An equilibrium mixture of alternate quaternary structure assemblies can form a basis for allostery. The morpheein model of allostery is a concerted dissociative model that describes an equilibrium of alternate quaternary structure assemblies whose architectures are dictated by alternate conformations in the dissociated state. Kinetic and biophysical anomalies that suggest that the morpheein model of allostery applies for a given protein of interest are briefly described. Two methods are presented for evaluating proteins as potential morpheeins. One is a subunit interchange method that uses chromatography, dialysis, and mass spectroscopy to monitor changes in multimer composition. The other is a two-dimensional native gel electrophoresis method to monitor ligand-induced changes in an equilibrium of alternate multimeric assemblies.
Collapse
|
15
|
Tenhaken R, Voglas E, Cock JM, Neu V, Huber CG. Characterization of GDP-mannose dehydrogenase from the brown alga Ectocarpus siliculosus providing the precursor for the alginate polymer. J Biol Chem 2011; 286:16707-15. [PMID: 21454608 PMCID: PMC3089512 DOI: 10.1074/jbc.m111.230979] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 03/22/2011] [Indexed: 11/06/2022] Open
Abstract
Alginate is a major cell wall polymer of brown algae. The precursor for the polymer is GDP-mannuronic acid, which is believed to be derived from a four-electron oxidation of GDP-mannose through the enzyme GDP-mannose dehydrogenase (GMD). So far no eukaryotic GMD has been biochemically characterized. We have identified a candidate gene in the Ectocarpus siliculosus genome and expressed it as a recombinant protein in Escherichia coli. The GMD from Ectocarpus differs strongly from related enzymes in bacteria and is as distant to the bacterial proteins as it is to the group of UDP-glucose dehydrogenases. It lacks the C-terminal ∼120 amino acid domain present in bacterial GMDs, which is believed to be involved in catalysis. The GMD from brown algae is highly active at alkaline pH and contains a catalytic Cys residue, sensitive to heavy metals. The product GDP-mannuronic acid was analyzed by HPLC and mass spectroscopy. The K(m) for GDP-mannose was 95 μM, and 86 μM for NAD(+). No substrate other than GDP-mannose was oxidized by the enzyme. In gel filtration experiments the enzyme behaved as a dimer. The Ectocarpus GMD is stimulated by salts even at low molar concentrations as a possible adaptation to marine life. It is rapidly inactivated at temperatures above 30 °C.
Collapse
Affiliation(s)
- Raimund Tenhaken
- Department of Cell Biology, Division of Plant Physiology, University of Salzburg, 5020 Salzburg, Austria.
| | | | | | | | | |
Collapse
|
16
|
Chuang GY, Mehra-Chaudhary R, Ngan CH, Zerbe BS, Kozakov D, Vajda S, Beamer LJ. Domain motion and interdomain hot spots in a multidomain enzyme. Protein Sci 2011; 19:1662-72. [PMID: 20589904 DOI: 10.1002/pro.446] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The aim of this article is to analyze conformational changes by comparing 10 different structures of Pseudomonas aeruginosa phosphomannomutase/phosphoglucomutase (PMM/PGM), a four-domain enzyme in which both substrate binding and catalysis require substantial movement of the C-terminal domain. We focus on changes in interdomain and active site crevices using a method called computational solvent mapping rather than superimposing the structures. The method places molecular probes (i.e., small organic molecules containing various functional groups) around the protein to find hot spots. One of the most important hot spots is in the active site, consistent with the ability of the enzyme to bind both glucose and mannose phosphosugar substrates. The protein has eight additional hot spots at domain-domain interfaces and hinge regions. The locations and nature of six of these hot spots vary between the open, half-open, and closed conformers of the enzyme, in good agreement with the ligand-induced conformational changes. In the closed structures the number of probe clusters at the hinge region significantly depends on the position of the phosphorylated oxygen in the substrate (e.g., glucose 1-phosphate versus glucose 6-phosphate), but the protein remains almost unchanged in terms of the overall RMSD, indicating that computational solvent mapping is a more sensitive approach to detect changes in binding sites and interdomain crevices. Focusing on multidomain proteins we show that the subresolution conformational differences revealed by the mapping are in fact significant, and present a general statistical method of analysis to determine the significance of rigid body domain movements in X-ray structures.
Collapse
Affiliation(s)
- Gwo-Yu Chuang
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | | | | | | | | | | | | |
Collapse
|
17
|
Huang W, Llano J, Gauld JW. A DFT study on the catalytic mechanism of UDP-glucose dehydrogenase. CAN J CHEM 2010. [DOI: 10.1139/v10-044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Uridine 5′-diphosphate glucuronic acid (UDPGlcUA) is a key intermediary metabolite in many species, including pathogenic bacteria and humans. It is biosynthesized from UDP-glucose (UDPGlc) by uridine diphosphate glucose dehydrogenase (UDPGlcDH) via a twofold two-electron–one-proton oxidation that successively transforms the 6-hydroxymethyl of glucopyranose into a formyl, and the latter into the final carboxylic function. The catalytic mechanism of UDPGlcDH was investigated using a large enzyme active-site model in combination with the B3LYP method and the polarizable continuum model (IEF-PCM) self-consistent reaction field. The latter was used to correct for the long-range electrostatic effect of the protein environment. The overall mechanism consists of four catalytic steps: (i) NAD+-dependent oxidation of glucose to glucuronaldehyde, (ii) nucleophilic addition of Cys260–SH to glucuronaldehyde to form a 6-thiohemiacetal intermediate, (iii) NAD+-dependent oxidation of the 6-thiohemiacetal to form a 6-thioester intermediate, and finally, (iv) hydrolysis of the 6-thioester to give glucuronic acid. In addition, this study also provides insight into the debated roles of Lys204 and Asp264, and the most likely protonation state of a reactive Michaelis complex of UDPGlcDH.
Collapse
Affiliation(s)
- WenJuan Huang
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON N9B 3P4, Canada
| | - Jorge Llano
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON N9B 3P4, Canada
| | - James W. Gauld
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON N9B 3P4, Canada
| |
Collapse
|
18
|
Alginate Production: Precursor Biosynthesis, Polymerization and Secretion. ALGINATES: BIOLOGY AND APPLICATIONS 2009. [DOI: 10.1007/978-3-540-92679-5_2] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
|
19
|
Van Lanen SG, Oh TJ, Liu W, Wendt-Pienkowski E, Shen B. Characterization of the maduropeptin biosynthetic gene cluster from Actinomadura madurae ATCC 39144 supporting a unifying paradigm for enediyne biosynthesis. J Am Chem Soc 2007; 129:13082-94. [PMID: 17918933 PMCID: PMC2529154 DOI: 10.1021/ja073275o] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The biosynthetic gene cluster for the enediyne antitumor antibiotic maduropeptin (MDP) from Actinomadura madurae ATCC 39144 was cloned and sequenced. Cloning of the mdp gene cluster was confirmed by heterologous complementation of enediyne polyketide synthase (PKS) mutants from the C-1027 producer Streptomyces globisporus and the neocarzinostatin producer Streptomyces carzinostaticus using the MDP enediyne PKS and associated genes. Furthermore, MDP was produced, and its apoprotein was isolated and N-terminal sequenced; the encoding gene, mdpA, was found to reside within the cluster. The biosynthesis of MDP is highlighted by two iterative type I PKSs--the enediyne PKS and a 6-methylsalicylic acid PKS; generation of (S)-3-(2-chloro-3-hydroxy-4-methoxyphenyl)-3-hydroxypropionic acid derived from L-alpha-tyrosine; a unique type of enediyne apoprotein; and a convergent biosynthetic approach to the final MDP chromophore. The results demonstrate a platform for engineering new enediynes by combinatorial biosynthesis and establish a unified paradigm for the biosynthesis of enediyne polyketides.
Collapse
Affiliation(s)
| | | | - Wen Liu
- Division of Pharmaceutical Sciences
| | | | - Ben Shen
- Division of Pharmaceutical Sciences
- University of Wisconsin National Cooperative Drug Discovery Group
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53705
| |
Collapse
|
20
|
Regni C, Schramm AM, Beamer LJ. The Reaction of Phosphohexomutase from Pseudomonas aeruginosa. J Biol Chem 2006; 281:15564-71. [PMID: 16595672 DOI: 10.1074/jbc.m600590200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) from Pseudomonas aeruginosa catalyzes the reversible conversion of 1-phospho to 6-phospho-sugars. The reaction entails two phosphoryl transfers, with an intervening 180 degrees reorientation of the reaction intermediate (e.g. glucose 1,6-bisphosphate) during catalysis. Reorientation of the intermediate occurs without dissociation from the active site of the enzyme and is, thus, a simple example of processivity, as defined by multiple rounds of catalysis without release of substrate. Structural characterization of two PMM/PGM-intermediate complexes with glucose 1,6-bisphosphate provides new insights into the reaction catalyzed by the enzyme, including the reorientation of the intermediate. Kinetic analyses of site-directed mutants prompted by the structural studies reveal active site residues critical for maintaining association with glucose 1,6-bisphosphate during its unique dynamic reorientation in the active site of PMM/PGM.
Collapse
Affiliation(s)
- Catherine Regni
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA
| | | | | |
Collapse
|
21
|
Jaffe EK. Morpheeins--a new structural paradigm for allosteric regulation. Trends Biochem Sci 2005; 30:490-7. [PMID: 16023348 DOI: 10.1016/j.tibs.2005.07.003] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Revised: 05/20/2005] [Accepted: 07/04/2005] [Indexed: 11/16/2022]
Abstract
Classic models for the allosteric regulation of protein function consider an equilibrium among protein structures of constant oligomeric multiplicity. The morpheein (mor-phee'-in) concept expands this model to include a dynamic equilibrium of protein structures wherein a protein monomer can exist in more than one conformation and each monomer conformation dictates a different quaternary structure of finite multiplicity and different functionality. The morpheein concept provides a new framework for understanding allosteric regulation, kinetic cooperativity and hysteresis. Porphobilinogen synthase constitutes a prototype morpheein ensemble comprising several interconverting quaternary structure isoforms; one monomer conformation dictates assembly of a high-activity octamer, whereas an alternative monomer conformation dictates assembly of a low-activity hexamer. It is proposed here that the behavior of some other allosteric enzymes reflect dynamic morpheein equilibrium systems and six candidate proteins are enumerated.
Collapse
Affiliation(s)
- Eileen K Jaffe
- BioMolecular Structure and Function Group, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
| |
Collapse
|
22
|
Kimmel JL, Tipton PA. Inactivation of GDP-mannose dehydrogenase from Pseudomonas aeruginosa by penicillic acid identifies a critical active site loop. Arch Biochem Biophys 2005; 441:132-40. [PMID: 16111644 DOI: 10.1016/j.abb.2005.06.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2005] [Revised: 06/27/2005] [Accepted: 06/29/2005] [Indexed: 10/25/2022]
Abstract
The pathogenic bacterium Pseudomonas aeruginosa synthesizes alginate as one of a group of virulence factors that are produced during infections. The enzyme GDP-mannose dehydrogenase catalyzes the committed step in alginate biosynthesis. We show here that penicillic acid is an irreversible inactivator of GDP-mannose dehydrogenase. Inactivation occurs with a rate constant of 0.39+/-0.01 mM(-1) min(-1) at pH 8.0, and does not exhibit saturation behavior. Partial protection from inactivation is afforded by GDP-mannose, but not by the other substrate, NAD+. GMP and NAD+ together provide complete protection against inactivation. Analysis by mass spectrometry confirmed that the enzyme is alkylated at multiple cysteine residues by penicillic acid, including Cys 213, Cys 246, and the active site cysteine, Cys 268. However, the pH dependence of the inactivation rate suggested that alkylation of a single cysteine residue is sufficient to inactivate the enzyme. The C268A mutant protein was also susceptible to inactivation by penicillic acid. The presence of NAD+ and GMP provided partial protection of Cys 246 and Cys 268, and almost complete protection of Cys 213. Cys 213 is located on a helix that forms part of the binding pocket for GDP-mannose, and forms a hydrogen bond with Asn 252. Asn 252 is located on a loop that surrounds GDP-mannose. The C213A mutant enzyme exhibits a Vmax that is 1.8-fold greater than the wild-type enzyme, suggesting that the interaction between Cys 213 and Asn 252 helps to hold the loop in place during catalysis, and that opening the loop to release product is partially rate-limiting. Cys 246 is adjacent to the GDP-mannose binding loop, and its alkylation may also interfere with loop movement.
Collapse
Affiliation(s)
- Jennifer L Kimmel
- Department of Biochemistry, University of Missouri-Columbia, Columbia, MO 65211, USA
| | | |
Collapse
|
23
|
Miller WL, Wenzel CQ, Daniels C, Larocque S, Brisson JR, Lam JS. Biochemical characterization of WbpA, a UDP-N-acetyl-D-glucosamine 6-dehydrogenase involved in O-antigen biosynthesis in Pseudomonas aeruginosa PAO1. J Biol Chem 2004; 279:37551-8. [PMID: 15226302 DOI: 10.1074/jbc.m404749200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
WbpA (PA3159) is an enzyme involved in the biosynthesis of unusual di-N-acetyl-d-mannosaminuronic acid-derived sugar nucleotides found in the O antigen of Pseudomonas aeruginosa PAO1 (serotype O5). The wbpA gene that encodes this enzyme was cloned into pET-28a, overexpressed as a histidine-tagged fusion protein, and purified by nickel chelation chromatography. Capillary electrophoresis was used to examine substrate conversion by WbpA, and the data revealed that WbpA is a UDP-N-acetyl-D-glucosamine 6-dehydrogenase (EC 1.1.1.136), which uses NAD(+) as a coenzyme. The enzyme reaction product was purified by HPLC and analyzed using NMR spectroscopy. Our results showed unequivocally that the product of the WbpA reaction is UDP-N-acetyl-d-glucosaminuronic acid. WbpA requires either NH(4)(+) or K(+) for activity and the accompanying anions exert secondary effects on activity consistent with their ranking in the Hofmeister series. Kinetic analysis showed positive cooperativity with respect to UDP-N-acetyl-d-glucosamine binding with a K(0.5) of 94 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.8. In addition, WbpA has a K(0.5) for NAD(+) of 220 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.1. The oligomerization state of WbpA was analyzed by gel filtration, dynamic light scattering, and analytical ultracentrifugation, with all three techniques indicating that WbpA exists as a trimer in solution. However, tertiary structure predictions suggested a tetramer, which was supported by data from transmission electron microscopy. The electron micrograph of negatively stained WbpA samples revealed structures with 4-fold symmetry.
Collapse
Affiliation(s)
- Wayne L Miller
- Department of Microbiology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | | | | | | | | | | |
Collapse
|
24
|
Ge X, Penney LC, van de Rijn I, Tanner ME. Active site residues and mechanism of UDP-glucose dehydrogenase. ACTA ACUST UNITED AC 2004; 271:14-22. [PMID: 14686915 DOI: 10.1046/j.1432-1033.2003.03876.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
UDP-glucose dehydrogenase catalyzes the NAD+-dependent twofold oxidation of UDP-glucose to give UDP-glucuronic acid. A sequestered aldehyde intermediate is produced in the first oxidation step and a covalently bound thioester is produced in the second oxidation step. This work demonstrates that the Streptococcus pyogenes enzyme incorporates a single solvent-derived oxygen atom during catalysis and probably does not generate an imine intermediate. The reaction of UDP-[6",6"-di-2H]-d-glucose is not accompanied by a primary kinetic isotope effect, indicating that hydride transfer is not rate determining in this reaction. Studies with a mutant of the key active site nucleophile, Cys260Ala, show that it is capable of both reducing the aldehyde intermediate, and oxidizing the hydrated form of the aldehyde intermediate but is incapable of oxidizing UDP-glucose to UDP-glucuronic acid. In the latter case, a ternary Cys260Ala/aldehyde intermediate/NADH complex is presumably formed, but it does not proceed to product as both release and hydration of the bound aldehyde occur slowly. A washout experiment demonstrates that the NADH in this ternary complex is not exchangeable with external NADH, indicating that dissociation only occurs after the addition of a nucleophile to the aldehyde carbonyl. Studies on Thr118Ala show that the value of kcat is reduced 160-fold by this mutation, and that the reaction of UDP-D-[6",6"-di-2H]-glucose is now accompanied by a primary kinetic isotope effect. This indicates that the barriers for the hydride transfer steps have been selectively increased and supports a mechanism in which an ordered water molecule (H-bonded to Thr118) serves as the catalytic base in these steps.
Collapse
Affiliation(s)
- Xue Ge
- Department of Chemistry, University of British Columbia, Vancouver, Canada
| | | | | | | |
Collapse
|
25
|
Grangeasse C, Obadia B, Mijakovic I, Deutscher J, Cozzone AJ, Doublet P. Autophosphorylation of the Escherichia coli protein kinase Wzc regulates tyrosine phosphorylation of Ugd, a UDP-glucose dehydrogenase. J Biol Chem 2003; 278:39323-9. [PMID: 12851388 DOI: 10.1074/jbc.m305134200] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Autophosphorylation of protein-tyrosine kinases (PTKs) involved in exopolysaccharide and capsular polysaccharide biosynthesis and transport has been observed in a number of Gram-negative and Gram-positive bacteria. However, besides their own phosphorylation, little is known about other substrates targeted by these protein-modifying enzymes. Here, we present evidence that the protein-tyrosine kinase Wzc of Escherichia coli is able to phosphorylate an endogenous enzyme, UDP-glucose dehydrogenase (Ugd), which participates in the synthesis of the exopolysaccharide colanic acid. The process of phosphorylation of Ugd by Wzc was shown to be stimulated by previous autophosphorylation of Wzc on tyrosine 569. The phosphorylation of Ugd was demonstrated to actually occur on tyrosine and result in a significant increase of its dehydrogenase activity. In addition, the phosphotyrosine-protein phosphatase Wzb, which is known to effectively dephosphorylate Wzc, exhibited only a low effect, if any, on the dephosphorylation of Ugd. These data were related to the recent observation that two other UDP-glucose dehydrogenases have been also shown to be phosphorylated by a PTK in the Gram-positive bacterium Bacillus subtilis. Comparative analysis of the activities of PTKs from Gram-negative and Gram-positive bacteria showed that they are regulated by different mechanisms that involve, respectively, either the autophosphorylation of kinases or their interaction with a membrane protein activator.
Collapse
Affiliation(s)
- Christophe Grangeasse
- Institut de Biologie et Chimie des Protéines, CNRS, Université de Lyon, 69367 Lyon Cedex 07, France.
| | | | | | | | | | | |
Collapse
|
26
|
Abstract
The mode of action of extracellular protons on ATP-gated P2X2 receptors remains controversial as either enhancement or depression of ATP-mediated currents has been reported. By investigating, at different pH, the electrophysiological effect of ATP on P2X2 receptors and complementing it with receptor modelling, the present study suggests a unified mechanism for both potentiation and inactivation of ATP receptors by protons. Our experiments on patch-clamped PC12 cells showed that, on the same cell, mild acidification potentiated currents induced by low ATP concentrations (<0.1 mM) and attenuated responses to high ATP concentrations (>1 mM) with emergence of current fading and rebound. To clarify the nature of the ATP/H+ interaction, we used the Ding and Sachs's "loop" receptor model which best describes the behavior of such receptors with two open states linked via one inactivated state. No effects by protons could be ascribed to H+-mediated open channel block. However, by assuming that protons facilitated binding of ATP to resting as well as open receptors, the model could closely replicate H+-induced potentiation of currents evoked by low ATP doses plus fading and rebound induced by high ATP doses. The latter phenomenon was due to receptor transition to the inactive state. The present data suggest that the high concentration of protons released with ATP (and catecholamines) from secretory vesicles may allow a dual action of H+ on P2X2 receptors. This condition might also occur on P2X2 receptors of central neurons exposed to low pH during ischemia.
Collapse
Affiliation(s)
- Andrei Skorinkin
- Biophysics Sector, International School for Advanced Studies, via Beirut 4, Trieste 34014, Italy
| | | | | |
Collapse
|