TIM  - ab Barrel

PDB file 1HTI

This structure of Triose Phosphate Isomerase, co-crystallized with the transition state analog 2-phosphoglycolic acid, was solved by S. C. Mande et al., in 1994.

Suggested display options:

Color chain to distinguish the 2 copies of the enzyme in the dimer.
Display as cartoon.
Trace the path of the protein to visualize how alternating a-helices and b-strands form the ab barrel.
You may select protein-sheet and select change color to make the b-strands more prominent.
Question: How many a,b motifs are in the ab barrel?

To visualize the transition state analog phosphoglycolate, select hetero-ligand, display as ball & sticks or sticks, and color CPK.

To visualize residues thought to participate in acid base catalysis, use the command line to select glu165, his95, display as sticks, and color CPK.
Note the location of these active site groups relative to the transition state analog. Keep in mind that phosphoglycolate is one C shorter than the normal substrate.
Question: On which side of the a,b barrel is the active site located? (C-terminal or N-terminal ends of b-strands?)

Substrate binding causes a loop consisting of residues 168-177 to shift position, covering the active site and stabilizing the transition state (discussed p. 392).
Compare the position of this loop in the 2 copies of the enzyme, only one of which has bound phosphoglycolate.

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