Triose Phosphate Isomerase Structure & Mechanism

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<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 name= "lodi">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 name="lodi" /> 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 name= "dab" />
<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 name= "lodi">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 name="lodi" /> 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 name= "dab" />
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[[Image:ckrenkmechanism.jpg|left|thumb|650px| '''Mechanism of Triose phosphate isomerase'''. Created by Christian Krenk using Spartan 08.]]
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[[Image:ckrenkmechanism.jpg|left|thumb|400px| '''Mechanism of Triose phosphate isomerase'''. Created by Christian Krenk using Spartan 08.]]
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 name="book" /> Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.<ref name="book" />
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 name="book" /> Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.<ref name="book" />

Revision as of 12:49, 8 September 2022

Human triosephosphate isomerase complex with phosphoglycolic acid 1hti

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References

  1. ↑ 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
  2. ↑ 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
  3. ↑ 3.0 3.1 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
  4. ↑ 4.0 4.1 4.2 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.
  5. ↑ 5.0 5.1 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
  6. ↑ 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

7. Wierenga RK, Kapetaniou EG, Venkatesan R. Triosephosphate isomerase: a highly evolved biocatalyst. Cellular and Molecular Life Sciences. 2010 August 7 67:3961-3982. PMID: 20694739 [1]

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