Triose Phosphate Isomerase Structure & Mechanism: Difference between revisions

Proteopedia Page Contributors and Editors (what is this?)Proteopedia Page Contributors and Editors (what is this?)

@@ Line 12: / Line 12: @@
 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.
 <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>  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.
+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.  Without the loop, the enediol intermediate would eliminate phosphate, with the end products being inorganic phosphate and toxic methylglyoxal.