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-Mention Importance of Cationic Hydrogen donor |
-Mention Importance of Cationic Hydrogen donor |
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The addition of chorismate mutase, increases the rate of the reaction a million fold. |
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Current Mechanism section: |
Current Mechanism section: |
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The conversion of chorismate to prephenate is the first [[committed step]] in the pathway to the production of the aromatic amino acids: tyrosine and phenylalanine. In the absence of enzyme catalysis this mechanism proceeds as a concerted, but asynchronous step and is an [[exergonic]] process. The mechanism for this transformation is formally a [[Claisen rearrangement|Claisen rearrangement,]] supported by the kinetic and isotopic data reported by Knowles, et al.<ref>{{Cite journal|last=Gray|first=Joseph V.|last2=Knowles|first2=Jeremy R.|date=1994-08-01|title=Monofunctional Chorismate Mutase from Bacillus subtilis: FTIR Studies and the Mechanism of Action of the Enzyme|url=http://dx.doi.org/10.1021/bi00199a018|journal=Biochemistry|volume=33|issue=33|pages=9953–9959|doi=10.1021/bi00199a018|issn=0006-2960}}</ref> In the enzyme active site, interactions between specific residues and the substrate restrict conformational degrees of freedom, such that the entropy of activation is effectively reduced to zero, and thereby promotes catalysis. As a result, there is no formal intermediate, but rather a pseudo-diaxial chair-like transition state. Evidence for this conformation is provided by an inverse secondary [[kinetic isotope effect]] at .<ref |
The conversion of chorismate to prephenate is the first [[committed step]] in the pathway to the production of the aromatic amino acids: tyrosine and phenylalanine. The presence of chorismate mutase, increases the rate of the reaction a million fold.<ref name=":0">{{Cite journal|last=Lee|first=Ay|last2=Stewart|first2=J.D.|last3=Clardy|first3=J.|last4=Ganem|first4=B.|title=New insight into the catalytic mechanism of chorismate mutases from structural studies|url=http://dx.doi.org/10.1016/1074-5521(95)90269-4|journal=Chemistry & Biology|volume=2|issue=4|pages=195–203|doi=10.1016/1074-5521(95)90269-4}}</ref> In the absence of enzyme catalysis this mechanism proceeds as a concerted, but asynchronous step and is an [[exergonic]] process. The mechanism for this transformation is formally a [[Claisen rearrangement|Claisen rearrangement,]] supported by the kinetic and isotopic data reported by Knowles, et al.<ref>{{Cite journal|last=Gray|first=Joseph V.|last2=Knowles|first2=Jeremy R.|date=1994-08-01|title=Monofunctional Chorismate Mutase from Bacillus subtilis: FTIR Studies and the Mechanism of Action of the Enzyme|url=http://dx.doi.org/10.1021/bi00199a018|journal=Biochemistry|volume=33|issue=33|pages=9953–9959|doi=10.1021/bi00199a018|issn=0006-2960}}</ref> In the enzyme active site, interactions between specific residues and the substrate restrict conformational degrees of freedom, such that the entropy of activation is effectively reduced to zero, and thereby promotes catalysis. As a result, there is no formal intermediate, but rather a pseudo-diaxial chair-like transition state. Evidence for this conformation is provided by an inverse secondary [[kinetic isotope effect]] at the carbon directly attached to the hydroxyl group.<ref name=":0" /> This seemingly unfavorable arrangement is achieved through a series of electrostatic interactions, which rotate the extended chain of chorismate into the conformation required for this concerted mechanism. |
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This seemingly unfavorable arrangement is achieved through a series of electrostatic interactions, which rotate the extended chain of chorismate into the conformation required for this concerted mechanism. |
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An additional stabilizing factor in this enzyme-substrate complex is hydrogen bonding between the lone pair of the oxygen in the vinyl ether system and hydrogen bond donor residue. Not only does this stabilize the complex, but disruption of resonance within the vinyl ether destabilizes the ground state and reduces the energy barrier for this transformation. |
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An additional stabilizing factor in this enzyme-substrate complex is hydrogen bonding between the lone pair of the oxygen in the vinyl ether system and hydrogen bond donor residues. Not only does this stabilize the complex, but disruption of resonance within the vinyl ether destabilizes the ground state and reduces the energy barrier for this transformation. An alternative view is that electrostatic stabilization of the polarized transition state is of great importance in this reaction. This is shown in mutants of the native enzyme in which Arg90 is replaced with citrulline to demonstrate the importance of hydrogen bonding to stabilize the transition state.<ref>{{Cite journal|last=Kienhöfer|first=Alexander|last2=Kast|first2=Peter|last3=Hilvert|first3=Donald|date=2003-03-01|title=Selective Stabilization of the Chorismate Mutase Transition State by a Positively Charged Hydrogen Bond Donor|url=http://dx.doi.org/10.1021/ja0341992|journal=Journal of the American Chemical Society|volume=125|issue=11|pages=3206–3207|doi=10.1021/ja0341992|issn=0002-7863}}</ref> Other work using chorismate mutase from ''Bacillus subtilis'' showed evidence that when a [[cation]] was aptly placed in the active site, the electrostatic interactions between it and the negatively charged transition state promoted catalysis.<ref>{{Cite journal|last=Kast|first=Peter|last2=Grisostomi|first2=Corinna|last3=Chen|first3=Irene A.|last4=Li|first4=Songlin|last5=Krengel|first5=Ute|last6=Xue|first6=Yafeng|last7=Hilvert|first7=Donald|date=2000-11-24|title=A Strategically Positioned Cation Is Crucial for Efficient Catalysis by Chorismate Mutase|url=http://www.jbc.org/content/275/47/36832|journal=Journal of Biological Chemistry|language=en|volume=275|issue=47|pages=36832–36838|doi=10.1074/jbc.M006351200|issn=0021-9258|pmid=10960481}}</ref> |
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Additional studies have been done on the near attack conformer (NAC) of the reaction catalyzed by chorismate mutase. This NAC is the reactive conformation of the ground state that is directly converted to the transition state in the enzyme. Using [[thermodynamic integration]] (TI) methods, the standard free energies (ΔG<sub>N</sub><sup>°</sup>) for NAC formation were calculated in six different environments. The data obtained suggests that effective catalysis is derived from stabilization of both the NAC and transition state.<ref>{{Cite journal|last=Hur|first=Sun|last2=Bruice|first2=Thomas C.|date=2003-10-14|title=The near attack conformation approach to the study of the chorismate to prephenate reaction|url=http://www.pnas.org/content/100/21/12015|journal=Proceedings of the National Academy of Sciences|language=en|volume=100|issue=21|pages=12015–12020|doi=10.1073/pnas.1534873100|issn=0027-8424|pmc=PMC218705|pmid=14523243}}</ref> However, other experimental evidence supports that the NAC effect observed is simply a result of electrostatic transition state stabilization.<ref>{{Cite journal|last=Štrajbl|first=Marek|last2=Shurki|first2=Avital|last3=Kato|first3=Mitsunori|last4=Warshel|first4=Arieh|date=2003-08-01|title=Apparent NAC Effect in Chorismate Mutase Reflects Electrostatic Transition State Stabilization|url=http://dx.doi.org/10.1021/ja0356481|journal=Journal of the American Chemical Society|volume=125|issue=34|pages=10228–10237|doi=10.1021/ja0356481|issn=0002-7863}}</ref> |
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| ⚫ | Overall, there have been extensive studies on the exact mechanism of this reaction, but the rate-determining step has yet to be uncovered. Some questions that remain surrounding the mechanism are how conformational constraint of the flexible substrate, specific [[hydrogen bonding]] to the [[transition state]], and electrostatic interactions actually contribute to catalysis. |
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Studies have been done on the near attack conformer (NAC), which refers to the reactive conformation of the ground state that directly converts to the transition state, of the reaction catalyzed by chorismate mutase. Using [[thermodynamic integration]] (TI) methods, the standard free energies (ΔG<sub>N</sub><sup>°</sup>) for NAC formation were calculated in six different environments: water, wild-type enzymes from ''Escherichia coli'' (w-EcCM) and ''Bacillus subtilis'' (w-BsCM), the Arg90Cit mutant of BsCM and Glu52Ala mutant of EcCM, and the catalytic antibody 1F7. This data suggests that effective catalysis is derived from stabilization of both the NAC and transition state,<ref>{{Cite journal|last=Hur|first=Sun|last2=Bruice|first2=Thomas C.|date=2003-10-14|title=The near attack conformation approach to the study of the chorismate to prephenate reaction|url=http://www.pnas.org/content/100/21/12015|journal=Proceedings of the National Academy of Sciences|language=en|volume=100|issue=21|pages=12015–12020|doi=10.1073/pnas.1534873100|issn=0027-8424|pmc=PMC218705|pmid=14523243}}</ref> although other experimental evidence supports that the NAC effect observed is simply a result of electrostatic transition state stabilization.<ref>{{Cite journal|last=Štrajbl|first=Marek|last2=Shurki|first2=Avital|last3=Kato|first3=Mitsunori|last4=Warshel|first4=Arieh|date=2003-08-01|title=Apparent NAC Effect in Chorismate Mutase Reflects Electrostatic Transition State Stabilization|url=http://dx.doi.org/10.1021/ja0356481|journal=Journal of the American Chemical Society|volume=125|issue=34|pages=10228–10237|doi=10.1021/ja0356481|issn=0002-7863}}</ref> |
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[[User:GomezChristian|GomezChristian]] ([[User talk:GomezChristian|talk]]) 23:04, 26 February 2017 (UTC) |
[[User:GomezChristian|GomezChristian]] ([[User talk:GomezChristian|talk]]) 23:04, 26 February 2017 (UTC) |
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Revision as of 00:21, 27 February 2017
 | This is a user sandbox of GomezChristian. You can use it for testing or practicing edits. This is not the sandbox where you should draft your assigned article for a dashboard.wikiedu.org course. To find the right sandbox for your assignment, visit your Dashboard course page and follow the Sandbox Draft link for your assigned article in the My Articles section. |
Note: Group's draft space -GomezChristian (talk) 21:10, 21 February 2017 (UTC)
Evaluation of Chorismate Mutase Article:
1.Elaboration could be made on conformational trapping of the substrate in the enzyme active site.
2. Figures or schemes to illustrate the catalytic mechanism would aid in visualising the reaction.
3. Further discussion of thermodynamic factors that drive the reaction could be provided.
4. Figure for reaction has a misspelling of chorismate (chromismate). Charles Cole (talk) 21:41, 21 February 2017 (UTC)
Draft:
-Thermodinamic factors
-Importance of Substrate Conformation. Mention "pseudo-diaxial". Mention KIE as evidence.
-Substrate binding and Conformational Trapping. Nature of bonds.
-NAC
-Mention Importance of Cationic Hydrogen donor
Current Mechanism section:
The conversion of chorismate to prephenate is the first committed step in the pathway to the production of the aromatic amino acids: tyrosine and phenylalanine. The presence of chorismate mutase, increases the rate of the reaction a million fold.[1] In the absence of enzyme catalysis this mechanism proceeds as a concerted, but asynchronous step and is an exergonic process. The mechanism for this transformation is formally a Claisen rearrangement, supported by the kinetic and isotopic data reported by Knowles, et al.[2] In the enzyme active site, interactions between specific residues and the substrate restrict conformational degrees of freedom, such that the entropy of activation is effectively reduced to zero, and thereby promotes catalysis. As a result, there is no formal intermediate, but rather a pseudo-diaxial chair-like transition state. Evidence for this conformation is provided by an inverse secondary kinetic isotope effect at the carbon directly attached to the hydroxyl group.[1] This seemingly unfavorable arrangement is achieved through a series of electrostatic interactions, which rotate the extended chain of chorismate into the conformation required for this concerted mechanism.
An additional stabilizing factor in this enzyme-substrate complex is hydrogen bonding between the lone pair of the oxygen in the vinyl ether system and hydrogen bond donor residues. Not only does this stabilize the complex, but disruption of resonance within the vinyl ether destabilizes the ground state and reduces the energy barrier for this transformation. An alternative view is that electrostatic stabilization of the polarized transition state is of great importance in this reaction. This is shown in mutants of the native enzyme in which Arg90 is replaced with citrulline to demonstrate the importance of hydrogen bonding to stabilize the transition state.[3] Other work using chorismate mutase from Bacillus subtilis showed evidence that when a cation was aptly placed in the active site, the electrostatic interactions between it and the negatively charged transition state promoted catalysis.[4]
Additional studies have been done on the near attack conformer (NAC) of the reaction catalyzed by chorismate mutase. This NAC is the reactive conformation of the ground state that is directly converted to the transition state in the enzyme. Using thermodynamic integration (TI) methods, the standard free energies (ΔGN°) for NAC formation were calculated in six different environments. The data obtained suggests that effective catalysis is derived from stabilization of both the NAC and transition state.[5] However, other experimental evidence supports that the NAC effect observed is simply a result of electrostatic transition state stabilization.[6]
Overall, there have been extensive studies on the exact mechanism of this reaction, but the rate-determining step has yet to be uncovered. Some questions that remain surrounding the mechanism are how conformational constraint of the flexible substrate, specific hydrogen bonding to the transition state, and electrostatic interactions actually contribute to catalysis.
GomezChristian (talk) 23:04, 26 February 2017 (UTC)
- ^ a b Lee, Ay; Stewart, J.D.; Clardy, J.; Ganem, B. "New insight into the catalytic mechanism of chorismate mutases from structural studies". Chemistry & Biology. 2 (4): 195–203. doi:10.1016/1074-5521(95)90269-4.
- ^ Gray, Joseph V.; Knowles, Jeremy R. (1994-08-01). "Monofunctional Chorismate Mutase from Bacillus subtilis: FTIR Studies and the Mechanism of Action of the Enzyme". Biochemistry. 33 (33): 9953–9959. doi:10.1021/bi00199a018. ISSN 0006-2960.
- ^ Kienhöfer, Alexander; Kast, Peter; Hilvert, Donald (2003-03-01). "Selective Stabilization of the Chorismate Mutase Transition State by a Positively Charged Hydrogen Bond Donor". Journal of the American Chemical Society. 125 (11): 3206–3207. doi:10.1021/ja0341992. ISSN 0002-7863.
- ^ Kast, Peter; Grisostomi, Corinna; Chen, Irene A.; Li, Songlin; Krengel, Ute; Xue, Yafeng; Hilvert, Donald (2000-11-24). "A Strategically Positioned Cation Is Crucial for Efficient Catalysis by Chorismate Mutase". Journal of Biological Chemistry. 275 (47): 36832–36838. doi:10.1074/jbc.M006351200. ISSN 0021-9258. PMID 10960481.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Hur, Sun; Bruice, Thomas C. (2003-10-14). "The near attack conformation approach to the study of the chorismate to prephenate reaction". Proceedings of the National Academy of Sciences. 100 (21): 12015–12020. doi:10.1073/pnas.1534873100. ISSN 0027-8424. PMC 218705. PMID 14523243.
{{cite journal}}: CS1 maint: PMC format (link) - ^ Štrajbl, Marek; Shurki, Avital; Kato, Mitsunori; Warshel, Arieh (2003-08-01). "Apparent NAC Effect in Chorismate Mutase Reflects Electrostatic Transition State Stabilization". Journal of the American Chemical Society. 125 (34): 10228–10237. doi:10.1021/ja0356481. ISSN 0002-7863.