Triose Phosphate Isomerase: Difference between revisions
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== Structure & Function == | == Structure & Function == | ||
Triose Phosphate Isomerase is a member of the all alpha and beta (α/β) class of proteins and it is a homodimer consisting of two sequence-identical subunits (chains) each comprising 247 amino acids. Each TPI monomer (chain) contains the full set of catalytic residues; however, the enzyme is only active in the oligomeric form.<ref>PMID:18562316</ref> Therefore, dimerization is essential for full function of the enzyme even though it is not believed that any cooperativity exists between the two active sites.<ref>PMID: 2065677</ref> Each subunit contains 8 exterior <font color="#ff0080">'''alpha helices'''</font> surrounding 8 interior <font color="#d0a000">'''beta strands'''</font> | Triose Phosphate Isomerase is a member of the all alpha and beta (α/β) class of proteins and it is a homodimer consisting of two sequence-identical subunits (chains) each comprising 247 amino acids. Each TPI monomer (chain) contains the full set of catalytic residues; however, the enzyme is only active in the oligomeric form.<ref>PMID:18562316</ref> Therefore, dimerization is essential for full function of the enzyme even though it is not believed that any cooperativity exists between the two active sites.<ref>PMID: 2065677</ref> Each subunit contains 8 exterior <font color="#ff0080">'''alpha helices'''</font> surrounding 8 interior <font color="#d0a000">'''beta strands'''</font>, which form a <scene name='Triose_Phosphate_Isomerase/Helix_shaded_sheet_6/4'>conserved structural domain called a closed alpha/beta barrel</scene> (αβ) or more specifically a '''TIM barrel'''. The TIM barrel was originally named after TPI and is estimated to be present in 10% of all enzymes. Characteristic of most all TIM barrel domains is the presence of the enzyme's active site in the lower loop regions created by the eight loops that connect the C-termini of the beta strands with the N-termini of the alpha helices. TIM barrel proteins also share a structurally conserved phosphate binding motif, with the phosphate group found in the substrate or cofactors. <ref> http://www.ncbi.nlm.nih.gov/Structure/cdd/cddsrv</ref>. | ||
In each chain, nonpolar amino acids pointing inward from the beta strands contribute to the hydrophobic core of the structure (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/2'>hydrophobic/polar distribution of beta strands</scene>). The alpha helices are amphipathic: their outer (water-contacting) surfaces are polar, while their inner surfaces are largely hydrophobic (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/4'>hydrophobic/polar distribution of alpha helices</scene>). The loops are a mixture (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/6'>hydrophobic/polar distribution of loops</scene>). | In each chain, nonpolar amino acids pointing inward from the beta strands contribute to the hydrophobic core of the structure (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/2'>hydrophobic/polar distribution of beta strands</scene>). The alpha helices are amphipathic: their outer (water-contacting) surfaces are polar, while their inner surfaces are largely hydrophobic (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/4'>hydrophobic/polar distribution of alpha helices</scene>). The loops are a mixture (<scene name='Triose_Phosphate_Isomerase/Hydrophobicity_plus_cartoon/6'>hydrophobic/polar distribution of loops</scene>). | ||