Title
Structural basis for the magnesium-dependent activation of transketolase from Chlamydomonas reinhardtii
Author
Miriam Pasquini, Simona Fermani, Daniele Tedesco, Chiara Sciabolini, Pierre Crozet, Marina Naldi, Julien Henri, Ute Vothknecht, Carlo Bertucci, Stéphane D. Lemaire, Mirko Zaffagnini, Francesco Francia
Year
2017
Journal
Biochimica et Biophysica Acta (BBA) - General Subjects
Abstract
In photosynthetic organisms, transketolase (TK) is involved in the Calvin-Benson cycle and participates to the regeneration of ribulose-5-phosphate. Previous studies demonstrated that TK catalysis is strictly dependent on thiamine pyrophosphate (TPP) and divalent ions such as Mg2 +. TK from the unicellular green alga Chlamydomonas reinhardtii (CrTK) was recombinantly produced and purified to homogeneity. Biochemical properties of the CrTK enzyme were delineated by activity assays and its structural features determined by CD analysis and X-ray crystallography. CrTK is homodimeric and its catalysis depends on the reconstitution of the holo-enzyme in the presence of both TPP and Mg2 +. Activity measurements and CD analysis revealed that the formation of fully active holo-CrTK is Mg2 +-dependent and proceeds with a slow kinetics. The 3D–structure of CrTK without cofactors (CrTKapo) shows that two portions of the active site are flexible and disordered while they adopt an ordered conformation in the holo-form. Oxidative treatments revealed that Mg2 + participates in the redox control of CrTK by changing its propensity to be inactivated by oxidation. Indeed, the activity of holo-form is unaffected by oxidation whereas CrTK in the apo-form or reconstituted with the sole TPP show a strong sensitivity to oxidative inactivation. These evidences indicate that Mg2 + is fundamental to allow gradual conformational arrangements suited for optimal catalysis. Moreover, Mg2 + is involved in the control of redox sensitivity of CrTK.
Instrument
J-810
Keywords
Circular dichroism, Tertiary structure, Induced CD, Ligand binding, Biochemistry