A novel organization of ACT domains in allosteric enzymes revealed by the crystal structure of Arabidopsis aspartate kinase

Plant Cell. 2006 Jul;18(7):1681-92. doi: 10.1105/tpc.105.040451. Epub 2006 May 26.

Abstract

Asp kinase catalyzes the first step of the Asp-derived essential amino acid pathway in plants and microorganisms. Depending on the source organism, this enzyme contains up to four regulatory ACT domains and exhibits several isoforms under the control of a great variety of allosteric effectors. We report here the dimeric structure of a Lys and S-adenosylmethionine-sensitive Asp kinase isoform from Arabidopsis thaliana in complex with its two inhibitors. This work reveals the structure of an Asp kinase and an enzyme containing two ACT domains cocrystallized with its effectors. Only one ACT domain (ACT1) is implicated in effector binding. A loop involved in the binding of Lys and S-adenosylmethionine provides an explanation for the synergistic inhibition by these effectors. The presence of S-adenosylmethionine in the regulatory domain indicates that ACT domains are also able to bind nucleotides. The organization of ACT domains in the present structure is different from that observed in Thr deaminase and in the regulatory subunit of acetohydroxyacid synthase III.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Allosteric Regulation
  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Aspartate Kinase / antagonists & inhibitors
  • Aspartate Kinase / chemistry*
  • Aspartate Kinase / genetics
  • Aspartate Kinase / metabolism
  • Aspartic Acid / metabolism
  • Binding Sites
  • Catalytic Domain
  • Crystallography, X-Ray
  • Dimerization
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / chemistry
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Lysine / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Structure, Quaternary*
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Serine / metabolism

Substances

  • Arabidopsis Proteins
  • Isoenzymes
  • Protein Subunits
  • Aspartic Acid
  • Serine
  • Adenosine Triphosphate
  • Aspartate Kinase
  • Lysine

Associated data

  • PDB/2CDQ