Triose Phosphate Isomerase: Difference between revisions

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  nearly identical subunits each consisting of 247 amino acids and differing only at their N-terminal ends. Each TPI monomer 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 <scene name='Triose_Phosphate_Isomerase/Helix_shaded_sheet_3/1'>alpha helices</scene> surrounding 8 interior <scene name='Triose_Phosphate_Isomerase/Beta_sheet_labelled/1'>beta sheets</scene>, which form a conserved structural domain called a closed alpha/beta barrel (αβ) or more specifically a <scene name='Triose_Phosphate_Isomerase/Tim_barrel_2/1'>TIM Barrel</scene>. 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-terminus of the beta strands with the N-terminus of the alpha helices. TIM barrel proteins also share a structurally conserved phosphate binding motif, with the phosphate either coming from the substrate or from cofactors. <ref> http://www.ncbi.nlm.nih.gov/Structure/cdd/cddsrv</ref>.