Triose Phosphate Isomerase: Difference between revisions
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[[Image:TriosePhosphateIsomerase_Ribbon_pastel_photo_small.jpg|thumb|left|260px| Ribbon drawing of the "TIM barrel" fold]] | [[Image:TriosePhosphateIsomerase_Ribbon_pastel_photo_small.jpg|thumb|left|260px| Ribbon drawing of the "TIM barrel" fold]] | ||
==Introduction== | |||
[[Triose Phosphate Isomerase]] (TPI or TIM) is a ubiquitous dimeric enzyme with a molecular weight of ~54 kD (27 kD per subunit) which catalyzes the reversible interconversion of the triose phosphate isomers <scene name='Triose_Phosphate_Isomerase/Morph/1'>dihydroxyacetone phosphate (DHAP)</scene> and <scene name='Triose_Phosphate_Isomerase/Morph/2'>D-glyceraldehyde-3-phosphate (GAP)</scene>, an essential process in the glycolytic pathway. More simply, the enzyme catalyzes the <scene name='Triose_Phosphate_Isomerase/Morph/3'>isomerization of a ketose (DHAP) to an aldose (GAP)</scene>, also referred to as '''PGAL'''. In regards to the two isomers, at equilibrium, roughly 96% of the triose phosphate is in the DHAP isomer form; however, the isomerization reaction proceeds due to the rapid removal of GAP from the subsequent reactions of glycolysis. The TPI tertiary structure is the classic example of the "TIM barrel" fold (see image at left). The TPI structure is shown on the right (PDB entry [[2ypi]]) in complex with the inhibitor 2-phosphoglycolic acid (PGA), which is bound to each of its two active sites. TPI is an example of a catalytically perfect enzyme, indicating that for almost every enzyme-substrate encounter, a product is formed and that this interaction is limited only by the substrate diffusion rate. See [[Glycolysis Enzymes]] and [[Isomerases]]. | [[Triose Phosphate Isomerase]] (TPI or TIM) is a ubiquitous dimeric enzyme with a molecular weight of ~54 kD (27 kD per subunit) which catalyzes the reversible interconversion of the triose phosphate isomers <scene name='Triose_Phosphate_Isomerase/Morph/1'>dihydroxyacetone phosphate (DHAP)</scene> and <scene name='Triose_Phosphate_Isomerase/Morph/2'>D-glyceraldehyde-3-phosphate (GAP)</scene>, an essential process in the glycolytic pathway. More simply, the enzyme catalyzes the <scene name='Triose_Phosphate_Isomerase/Morph/3'>isomerization of a ketose (DHAP) to an aldose (GAP)</scene>, also referred to as '''PGAL'''. In regards to the two isomers, at equilibrium, roughly 96% of the triose phosphate is in the DHAP isomer form; however, the isomerization reaction proceeds due to the rapid removal of GAP from the subsequent reactions of glycolysis. The TPI tertiary structure is the classic example of the "TIM barrel" fold (see image at left). The TPI structure is shown on the right (PDB entry [[2ypi]]) in complex with the inhibitor 2-phosphoglycolic acid (PGA), which is bound to each of its two active sites. TPI is an example of a catalytically perfect enzyme, indicating that for almost every enzyme-substrate encounter, a product is formed and that this interaction is limited only by the substrate diffusion rate. See [[Glycolysis Enzymes]] and [[Isomerases]]. | ||
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One specific example of sequence homology is that of loop 6 and loop 7 residues, whose structural contributions are discussed above. In a sequence alignment of 133 TIM sequences, two highly conserved motifs are noticed. First, 114 sequences in loop 6 contain the PXW sequence family (where X is I,L or V in 112 sequences or otherwise a T or K). Secondly, loop 7 contains a highly conserved YGGS motif; however, this motif is only found when the N-terminal hinge contains tryptophan. | One specific example of sequence homology is that of loop 6 and loop 7 residues, whose structural contributions are discussed above. In a sequence alignment of 133 TIM sequences, two highly conserved motifs are noticed. First, 114 sequences in loop 6 contain the PXW sequence family (where X is I,L or V in 112 sequences or otherwise a T or K). Secondly, loop 7 contains a highly conserved YGGS motif; however, this motif is only found when the N-terminal hinge contains tryptophan. | ||
== 3D Structures of triose phosphate isomerase== | == 3D Structures of triose phosphate isomerase== | ||
[[Triose phosphate isomerase 3D structures]] | |||
</StructureSection> | |||
== Additional Resources == | == Additional Resources == | ||
*[[Carbohydrate Metabolism]] | *[[Carbohydrate Metabolism]] | ||