Structural Basis for Light Activation of a Chloroplast Enzyme: The Structure of Sorghum NADP-malate Dehydrogenase in Its Oxidized Form

Biochemistry. 1999 Apr 6;38(14):4319-26. doi: 10.1021/bi982876c.


Some key chloroplast enzymes are activated by light via a ferredoxin-thioredoxin reduction system which reduces disulfide bridges in the enzymes. We describe for the first time the structural basis for the redox activation of a chloroplast enzyme, the NADP-dependent malate dehydrogenase (MDH) from Sorghum vulgare whose structure has been determined and refined at 2.4 A resolution. In addition to the normal structural components of MDHs, the enzyme exhibits extensions at both the N- and C-termini, each of which contains a regulatory disulfide bridge which must be reduced for activation. The N-terminal disulfide motif is inserted in a cleft between the two subunits of the dimer, thereby locking the domains in each subunit. The C-terminal disulfide keeps the C-terminal residues tight to the enzyme surface and blocks access to the active site. Reduction of the N-terminal disulfide would release the stopper between the domains and give the enzyme the necessary flexibility. Simultaneous reduction of the C-terminal disulfide would free the C-terminal residues from binding to the enzyme and make the active site accessible.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Chloroplasts / enzymology*
  • Crystallization
  • Crystallography, X-Ray
  • Dimerization
  • Disulfides / chemistry
  • Enzyme Activation / genetics
  • Light*
  • Malate Dehydrogenase (NADP+)
  • Malate Dehydrogenase / antagonists & inhibitors
  • Malate Dehydrogenase / chemistry*
  • Malate Dehydrogenase / genetics
  • Malate Dehydrogenase / isolation & purification
  • Models, Molecular
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Peptide Fragments / antagonists & inhibitors
  • Peptide Fragments / chemistry
  • Plant Proteins / antagonists & inhibitors
  • Plant Proteins / chemistry*
  • Plant Proteins / genetics
  • Plant Proteins / isolation & purification
  • Recombinant Proteins / antagonists & inhibitors
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / isolation & purification


  • Disulfides
  • Peptide Fragments
  • Plant Proteins
  • Recombinant Proteins
  • Malate Dehydrogenase
  • Malate Dehydrogenase (NADP+)

Associated data

  • PDB/7MDH