2C2B: Crystallographic Structure Of Arabidopsis Thaliana Threonine Synthase Complexed With Pyridoxal Phosphate And S-adenosylmethionine

Threonine synthase (TS) is a fold-type II pyridoxal phosphate (PLP)-dependent enzyme that catalyzes the ultimate step of threonine synthesis in plants and microorganisms. Unlike the enzyme from microorganisms, plant TS is activated by S-adenosylmethionine (AdoMet). The mechanism of activation has remained unknown up to now. We report here the crystallographic structures of Arabidopsis thaliana TS in complex with PLP (aTS) and with PLP and AdoMet (aTS-AdoMet), which show with atomic detail how AdoMet activates TS. The aTS structure reveals a PLP orientation never previously observed for a type II PLP-dependent enzyme and explains the low activity of plant TS in the absence of its allosteric activator. The aTS-AdoMet structure shows that activation of the enzyme upon AdoMet binding triggers a large reorganization of active site loops in one monomer of the structural dimer and allows the displacement of PLP to its active conformation. Comparison with other TS structures shows that activation of the second monomer may be triggered by substrate binding. This structure also discloses a novel fold for two AdoMet binding sites located at the dimer interface, each site containing two AdoMet effectors bound in tandem. Moreover, aTS-AdoMet is the first structure of an enzyme that uses AdoMet as an allosteric effector.
PDB ID: 2C2BDownload
MMDB ID: 36236
PDB Deposition Date: 2005/9/27
Updated in MMDB: 2005/12
Experimental Method:
x-ray diffraction
Resolution: 2.6  Å
Source Organism:
Similar Structures:
Biological Unit for 2C2B: dimeric; determined by author and by software (PISA)
Molecular Components in 2C2B
Label Count Molecule
Proteins (2 molecules)
Threonine Synthase 1, Chloroplastic(Gene symbol: MTO2)
Molecule annotation
Chemicals (7 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB