IPP and enzymes

DDXXD

Highly conserved residue in terpene synthesis- Signature motif

What can we learn from the crystal structure of an enzyme?

Identify the substrate binding sites and the key residue in the SBS. Infer TPS enzyme reaction mechanisms. Provide a basis for site directed mutagenesis. provide deeper understanding of reaction mechanism, which can be ultimately used to design customized enzymes

Binding and dephosphorylation

Hydrophobic hydrocarbon inside enzyme and OPP outside. Magnesium and arginine positioned at substrate entry site heavily positively charged. DDXXD negatively charged residue at mouth to correctly position the magnesium. Partially negatively charged carbonyl groups from multiple Thr residues which don’t form hydrogen bonds in the alpha helix, pull the newly formed carbocation to the cavity and position the C1 in close proximity to C10 – C11 double bond

Stabilization and deprotonation

Asp Catalyses de protonation likes to take the oxygen. Tyr Is partially negative and stabilizes the carbocation giving more time for the reaction to occur

Immediate formation and re-protonation

Stable germacrene is generated, but it is not the final product. The second round of cyclization occurs by reputation of the germacrene. Cyclization and rearrangement will continue to go on until the carbocation intermediate is neutralized

Do enzymes that catalyze successive steps in a metabolic pathway evolve from one another

3-D core folding patterns of FPP synthase and TPS are identical

How is IPP synthesized

Through a mevalonic acid pathway in animals and plants. Acetyl CoA is a precursor for IPP, made from glycolysis. Six enzymes are involved in the conversion of acetyl CoA to IPP