Gallus gallus (chicken)
Triosephosphate isomerase was among some of the first protein structures studied by X-ray diffraction. It had one at the time of its structure discovery quite unusual shape, so unusual that the shape nowadays is referred to as the TIM barrel. However, there are actually many proteins, of differing amino acid sequences and functions, that possess this 3-dimensional shape. Whether this is the result of convergent or divergent evolution is unclear. Convergent evolution would be that different proteins develop to have similar shape because it facilitates their function. Divergent evolution would be that all known TIM barrel proteins have a common ancestor and developed to perform different functions. The protein here, the original triosephosphate isomerase, is involved in the processing of sugars, the glycolytic pathway. The product of TIM is the compound glyceraldehyde 3-phosphate (GAP). Since only this compound can continue the glycolytic pathway, TIM is an important component for the generation of energy by the body. Defects in the gene for TIM, leading to defective TIM protein, are related to various diseases.
The protein is a dimer consisting of two identical subunits. The monomers however form very close contacts with each other. The structure shown here also contains a small compound, phosphoglycohydroxamate. This is a chemical whose structure is similar of one of the intermediates of the substrate. The location of the compound marks the active site of the TIM protein. This location is the same in all TIM barrel protein, namely at the bottom of the TIM barrel, somewhat off-center from the barrel axis.
Protein Data Bank (PDB)
Zhang, Z. et al.; "Crystal structure of recombinant chicken triosephosphate isomerase- phosphoglycolohydroxamate complex at 1.8-Angstroms resolution."; Biochemistry; (1994) 33:2830-2837 PubMed:8130195
author: Arno Paehler