Triose Phosphate Isomerase Structure & Mechanism
From Proteopedia
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==Structural Characteristics of TIM== | ==Structural Characteristics of TIM== | ||
The secondary structure consists of 14 alpha helices and 8 beta sheets per monomer, making it fall in the SCOP category of alpha and beta proteins. The tertiary structure is a <scene name='Christian_Krenk_Sandbox/Alpha_beta_barrel/2'>alpha-beta barrel.</scene> | The secondary structure consists of 14 alpha helices and 8 beta sheets per monomer, making it fall in the SCOP category of alpha and beta proteins. The tertiary structure is a <scene name='Christian_Krenk_Sandbox/Alpha_beta_barrel/2'>alpha-beta barrel.</scene> | ||
| - | The quaternary structure is a homodimer. | + | The quaternary structure is a homodimer. The molecular weight of the enzyme is estimated at 57,400 Da.<ref>PMID:752201</ref> |
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The enzyme aids in catalysis by binding tightly to the enediol transition state. To convert GAP to the enediol intermediate, a proton is abstracted from C2 by a base and the carbonyl oxygen atom is protonated by an acid.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> | The enzyme aids in catalysis by binding tightly to the enediol transition state. To convert GAP to the enediol intermediate, a proton is abstracted from C2 by a base and the carbonyl oxygen atom is protonated by an acid.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> | ||
| - | <scene name='Christian_Krenk_Sandbox/Active_site/1'> Glu 165 acts as the base and grabs the C2 proton on glyceraldehyde-3-phosphate, while His 95 is H-bonded to the carbonyl oxygen and acts as the acid by protonating carbonyl oxygen.</scene> The enediol intermediate is negatively charged, but is somewhat <scene name='Christian_Krenk_Sandbox/Lysine/1'>stabilized by the positively charged side chain of Lys 12.</scene> <ref>PMID:8130193</ref> Mutation of Lys 12 to Arg increases Km by a factor of 22 and decreases Vmax by a factor of 180.<ref>PMID:8130193</ref> To convert the enediol intermediate to DHAP, C1 is protonated by Glu 165, with His 95 removing a proton from C2’s OH group. As a result, the catalytic groups are back to their original states, and catalysis is complete. | + | <scene name='Christian_Krenk_Sandbox/Active_site/1'> Glu 165 acts as the base and grabs the C2 proton on glyceraldehyde-3-phosphate, while His 95 is H-bonded to the carbonyl oxygen and acts as the acid by protonating carbonyl oxygen.</scene> The enediol intermediate is negatively charged, but is somewhat <scene name='Christian_Krenk_Sandbox/Lysine/1'>stabilized by the positively charged side chain of Lys 12.</scene> <ref>PMID:8130193</ref> Mutation of Lys 12 to Arg increases Km by a factor of 22 and decreases Vmax by a factor of 180.<ref>PMID:8130193</ref> To convert the enediol intermediate to DHAP, C1 is protonated by Glu 165, with His 95 removing a proton from C2’s OH group. As a result, the catalytic groups are back to their original states, and catalysis is complete. With GAP as a substrate, Km for the reaction is .34 mM and Vmax is 7200 units/mg protein at 25 degrees C and pH 7.5.<ref>PMID:752201</ref> |
An interesting part of the enzyme is the <scene name='Christian_Krenk_Sandbox/Flexible_loop/1'>flexible loop</scene> that stabilizes the enediol-like transition state. The flexible loop (residues 167-176)<ref>PMID:2204418</ref> closes over the active site like a hinged lid when substrate is bound, thus preventing phosphate from leaving. A four-residue segment of the loop H-bonds with the phosphate group of the substrate.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> | An interesting part of the enzyme is the <scene name='Christian_Krenk_Sandbox/Flexible_loop/1'>flexible loop</scene> that stabilizes the enediol-like transition state. The flexible loop (residues 167-176)<ref>PMID:2204418</ref> closes over the active site like a hinged lid when substrate is bound, thus preventing phosphate from leaving. A four-residue segment of the loop H-bonds with the phosphate group of the substrate.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.</ref> | ||
Revision as of 20:14, 22 March 2010
Contents |
Triose Phosphate Isomerase (TIM)
Triose phosphate isomerase (TIM)[1][2] (PDB 1wyi and 1hti) is a crucial enzyme in the glycolytic pathway. reversibly converts the aldose Glyceraldehyde-3-phosphate (GAP) to the ketose Dihydroxyacetone phosphate (DHAP). The interconversion proceeds by an enediol intermediate.
Structural Characteristics of TIM
The secondary structure consists of 14 alpha helices and 8 beta sheets per monomer, making it fall in the SCOP category of alpha and beta proteins. The tertiary structure is a The quaternary structure is a homodimer. The molecular weight of the enzyme is estimated at 57,400 Da.[3]
Mechanism of TIM
The enzyme aids in catalysis by binding tightly to the enediol transition state. To convert GAP to the enediol intermediate, a proton is abstracted from C2 by a base and the carbonyl oxygen atom is protonated by an acid.[4] The enediol intermediate is negatively charged, but is somewhat [5] Mutation of Lys 12 to Arg increases Km by a factor of 22 and decreases Vmax by a factor of 180.[6] To convert the enediol intermediate to DHAP, C1 is protonated by Glu 165, with His 95 removing a proton from C2’s OH group. As a result, the catalytic groups are back to their original states, and catalysis is complete. With GAP as a substrate, Km for the reaction is .34 mM and Vmax is 7200 units/mg protein at 25 degrees C and pH 7.5.[7]
An interesting part of the enzyme is the that stabilizes the enediol-like transition state. The flexible loop (residues 167-176)[8] closes over the active site like a hinged lid when substrate is bound, thus preventing phosphate from leaving. A four-residue segment of the loop H-bonds with the phosphate group of the substrate.[9] Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.[10]
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| 1wyi, resolution 2.20Å () | |||||||||
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| Activity: | Triose-phosphate isomerase, with EC number 5.3.1.1 | ||||||||
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| Resources: | FirstGlance, OCA, RCSB, PDBsum | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
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| 1hti, resolution 2.80Å () | |||||||||
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| Ligands: | |||||||||
| Activity: | Triose-phosphate isomerase, with EC number 5.3.1.1 | ||||||||
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| Resources: | FirstGlance, OCA, RCSB, PDBsum | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
References
- ↑ Kinoshita T, Maruki R, Warizaya M, Nakajima H, Nishimura S. Structure of a high-resolution crystal form of human triosephosphate isomerase: improvement of crystals using the gel-tube method. Acta Crystallogr Sect F Struct Biol Cryst Commun. 2005 Apr 1;61(Pt, 4):346-9. Epub 2005 Mar 24. PMID:16511037 doi:10.1107/S1744309105008341
- ↑ Mande SC, Mainfroid V, Kalk KH, Goraj K, Martial JA, Hol WG. Crystal structure of recombinant human triosephosphate isomerase at 2.8 A resolution. Triosephosphate isomerase-related human genetic disorders and comparison with the trypanosomal enzyme. Protein Sci. 1994 May;3(5):810-21. PMID:8061610
- ↑ Dabrowska A, Kamrowska I, Baranowski T. Purification, crystallization and properties of triosephosphate isomerase from human skeletal muscle. Acta Biochim Pol. 1978;25(3):247-56. PMID:752201
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.
- ↑ Lodi PJ, Chang LC, Knowles JR, Komives EA. Triosephosphate isomerase requires a positively charged active site: the role of lysine-12. Biochemistry. 1994 Mar 15;33(10):2809-14. PMID:8130193
- ↑ Lodi PJ, Chang LC, Knowles JR, Komives EA. Triosephosphate isomerase requires a positively charged active site: the role of lysine-12. Biochemistry. 1994 Mar 15;33(10):2809-14. PMID:8130193
- ↑ Dabrowska A, Kamrowska I, Baranowski T. Purification, crystallization and properties of triosephosphate isomerase from human skeletal muscle. Acta Biochim Pol. 1978;25(3):247-56. PMID:752201
- ↑ Lolis E, Petsko GA. Crystallographic analysis of the complex between triosephosphate isomerase and 2-phosphoglycolate at 2.5-A resolution: implications for catalysis. Biochemistry. 1990 Jul 17;29(28):6619-25. PMID:2204418
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry Life at the Molecular Level. New York: John Wiley & Sons, 2008. p. 495. Print.
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