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Structure and Function of Cyanobacterial DHDPS and DHDPR.

Janni B Christensen1, T P Soares da Costa1, Pierre Faou1

  • 1Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Victoria 3086, Australia.

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This study characterizes dihydrodipicolinate synthase (DHDPS) and dihydrodipicolinate reductase (DHDPR) from cyanobacteria. Both enzymes form tetramers, revealing that bacterial and plant enzyme structures diverged after cyanobacteria evolved.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Evolutionary Biology

Background:

  • Lysine biosynthesis involves dihydrodipicolinate synthase (DHDPS) and dihydrodipicolinate reductase (DHDPR).
  • These enzymes exhibit varied oligomeric forms in bacteria and plants, suggesting evolutionary divergence.
  • Cyanobacteria represent a crucial evolutionary link between bacteria and plants.

Purpose of the Study:

  • To characterize the structure and function of DHDPS and DHDPR from the cyanobacterium Anabaena variabilis.
  • To investigate the evolutionary divergence of DHDPS and DHDPR quaternary structures.

Main Methods:

  • Cloning, expression, and purification of recombinant DHDPS and DHDPR.
  • Circular dichroism spectroscopy to confirm protein folding.
  • Enzymatic assays to determine activity.
  • Analytical ultracentrifugation to assess oligomeric state.
  • X-ray crystallography to determine enzyme structures.

Main Results:

  • Recombinant DHDPS and DHDPR from A. variabilis were successfully purified, folded, and enzymatically active.
  • Analytical ultracentrifugation confirmed that both enzymes form tetramers in solution.
  • Crystal structures revealed that both enzymes adopt the canonical bacterial tetrameric architecture.
  • The quaternary structures of DHDPS and DHDPR in cyanobacteria resemble those in bacteria.

Conclusions:

  • Cyanobacterial DHDPS and DHDPR exist as tetramers, consistent with bacterial forms.
  • The study provides structural insights into enzymes at the bacteria-plant evolutionary divergence point.
  • These findings suggest that the divergence in quaternary structure of DHDPS and DHDPR occurred after the evolution of cyanobacteria, differentiating them from plants.