TIM--you need it, and it's just that AWESOME!

Figure 1. Glycolysis pathway highlighting TIM role (Figure 14-2 from Leighner)

     Triose phosphate isomerase or TIM is the enzyme in the transitional step from the preparatory phase to the payoff phase in glycolysis. It isomerizes dehydroxyacetone phosphate to D-glyceraldehyde 3-phosphate. Without this enzyme, only one pyruvate would be generated per glucose molecule instead of two.

Figure 2. Isomerization reaction by TIM from SigmaAldrich

     TIM has been described as a nearly perfect enzyme because of its incredible turnover rate. It is so fast that it is only limited by the rate of diffusion of the substrates. It is made up of two homodimers and the protein is only active when the two monomers are together. The active site for the enzyme is located at the interface of the two monomers, but only the residues on one of the monomers is part of the active site. The buried active site stabilizes an enediolate intermediate.

Figure 3. Enediolate and sulfate bound to Triose phosphate isomerase (3PY2) 

     Lack-of-function mutations (most commonly E104D) cause a serious, progressive, neurological disease creatively entitled triose phosphate isomerase deficiency...yep, creative. The most common characteristic of this disease is hemolytic anemia--the abnormal breakdown of red blood cells.
     Trypanosoma brucei, the parasite that causes African sleeping sickness, also has this enzyme. However, it has an extra 22-amino acid fragment that is unique. It has been found to send responder signals to glycosomes: a subset of peroxisomes. This same TIM protein with the extra 22-amino acid fragment was put into a similar organism and it did not target the glycosomes. This presents a potential drug target for African sleeping sickness. It is, quite surprisingly, found in an enzyme shared by most organisms.


Resources:

Galland, N., de Walque, S., Voncken, F.G., Verlinde, C.L., Michels, P.A. “An internal sequence targets Trypanosoma brucei triosephosphate isomerase to glycosomes” Mol Biochem Parasitol 171.1 May (2010): 45-49. Medline. Wed. 28 Apr. 2011.

http://www.ncbi.nlm.nih.gov/pubmed/20138091

Orosz, F., Oláh, J. and Ovádi, J. (2006), Triosephosphate isomerase deficiency: Facts and doubts. IUBMB Life, 58: 703–715. doi: 10.1080/15216540601115960

http://onlinelibrary.wiley.com/doi/10.1080/15216540601115960/abstract

Wierenga, R K., E G. Kapetaniou, and R Venkatesan. "Triosephosphate isomerase: a highly evolved biocatalyst." Cell Mol Life Sci67.237 Aug. (2010): 3961-82. Medline. Web. 28 Apr. 2011.

http://www.ncbi.nlm.nih.gov/pubmed/20694739

The (Cool) Details

                TIM catalyzes the conversion of dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate in glycolysis. It has been described as a nearly perfect enzyme because its turnover rate is so fast that it is only limited by the rate of diffusion. If this enzyme is not working correctly, it is not possible 1 glucose molecule to be converted into 2 pyruvate molecules. Only half will be able to make it through the cycle. Lack-of-function mutations may occur in several locations, but the most common by far is E104D. These mutations cause a serious, progressive, neurological disorder creatively titled triose phosphate isomerase deficiency. It is characterized by chronic hemolytic anemia—the abnormal breakdown of red blood cells.

Orosz, F., Oláh, J. and Ovádi, J. (2006), Triosephosphate isomerase deficiency: Facts and doubts. IUBMB Life, 58: 703–
715. doi: 10.1080/15216540601115960
http://onlinelibrary.wiley.com/doi/10.1080/15216540601115960/abstract

TIM is made up of two hemolytic dimers. The protein is only functional as a dimer. The active site is located at the interface of the two monomers; however, the residues involved in binding are only on one of the monomers. The active site is buried in the center of the protein to exclude solvent. The buried active site stabilizes an enediolate intermediate.

Wierenga, R K., E G. Kapetaniou, and R Venkatesan. "Triosephosphate isomerase: a highly evolved biocatalyst." Cell Mol Life Sci67.237 Aug. (2010): 3961-82. Medline. Web. 28 Apr. 2011.
http://www.ncbi.nlm.nih.gov/pubmed/20694739

Trypanosoma brucei, the parasites that cause African sleeping sickness, have a unique 22-amino acid fragment that is buried in their triose phosphate isomerase enzymes. This amino acid fragment is capable of sending out a reporter protein to the glycosomes (a subgroup of peroxisomes). Triose phosphate isomerase is found almost exclusively in the cytosol. Mutations of similar organisms containing the fragment did not target the glycosomes. This presents a potential drug target for African sleeping sickness.

Galland, N., de Walque, S., Voncken, F.G., Verlinde, C.L., Michels, P.A. “An internal sequence targets Trypanosoma brucei triosephosphate isomerase to glycosomes” Mol Biochem Parasitol 171.1 May (2010): 45-49. Medline. Wed. 28 Apr. 2011.
http://www.ncbi.nlm.nih.gov/pubmed/20138091

Introduction of Structure

Triose Phosphate Isomerase     a.k.a TIM