Structural basis for a cofactor-dependent oxidation protection and catalysis of cyanobacterial succinic semialdehyde dehydrogenase

J Biol Chem. 2013 May 31;288(22):15760-70. doi: 10.1074/jbc.M113.460428. Epub 2013 Apr 15.


Succinic semialdehyde dehydrogenase (SSADH) from cyanobacterium Synechococcus differs from other SSADHs in the γ-aminobutyrate shunt. Synechococcus SSADH (SySSADH) is a TCA cycle enzyme and completes a 2-oxoglutarate dehydrogenase-deficient cyanobacterial TCA cycle through a detour metabolic pathway. SySSADH produces succinate in an NADP(+)-dependent manner with a single cysteine acting as the catalytic residue in the catalytic loop. Crystal structures of SySSADH were determined in their apo form, as a binary complex with NADP(+) and as a ternary complex with succinic semialdehyde and NADPH, providing details about the catalytic mechanism by revealing a covalent adduct of a cofactor with the catalytic cysteine in the binary complex and a proposed thiohemiacetal intermediate in the ternary complex. Further analyses showed that SySSADH is an oxidation-sensitive enzyme and that the formation of the NADP-cysteine adduct is a kinetically preferred event that protects the catalytic cysteine from H2O2-dependent oxidative stress. These structural and functional features of SySSADH provide a molecular basis for cofactor-dependent oxidation protection in 1-Cys SSADH, which is unique relative to other 2-Cys SSADHs employing a redox-dependent formation of a disulfide bridge.

Keywords: Aldehyde Dehydrogenase; Crystal Structure; Cysteine Oxidation; Dehydrogenase; Enzyme Structure; Hydrogen Peroxide; Tricarboxylic Acid (TCA) Cycle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Catalysis
  • Crystallography, X-Ray
  • Hydrogen Peroxide / chemistry
  • Hydrogen Peroxide / metabolism
  • Kinetics
  • NADP / chemistry*
  • NADP / metabolism
  • Oxidative Stress / physiology
  • Oxidative Stress / radiation effects
  • Protein Structure, Tertiary
  • Structure-Activity Relationship
  • Succinate-Semialdehyde Dehydrogenase / chemistry*
  • Succinate-Semialdehyde Dehydrogenase / metabolism
  • Synechococcus / enzymology*


  • Bacterial Proteins
  • NADP
  • Hydrogen Peroxide
  • Succinate-Semialdehyde Dehydrogenase

Associated data

  • PDB/4IT9
  • PDB/4ITA
  • PDB/4ITB