title: Structural basis for a cofactor-dependent oxidation protection and catalysis of cyanobacterial succinic semialdehyde dehydrogenase.
abstract: 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.
authors.affiliation: Department of Agricultural Biotechnology, Seoul National University, Seoul 151-921, Korea.
authors.forename: Jinseo
authors.initials: J
authors.lastname: Park
authors.forename: Sangkee
authors.initials: S
authors.lastname: Rhee
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D018360:Crystallography, X-Ray; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D009249:NADP / Q000737:chemistry* / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology / Q000528:radiation effects; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D050644:Succinate-Semialdehyde Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D046940:Synechococcus / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D009249:NADP; D006861:Hydrogen Peroxide; D050644:Succinate-Semialdehyde Dehydrogenase
keywords: Aldehyde Dehydrogenase; Crystal Structure; Cysteine Oxidation; Dehydrogenase; Enzyme Structure; Hydrogen Peroxide; Tricarboxylic Acid (TCA) Cycle