Coenzyme Site-directed Mutants of Photosynthetic A(4)-GAPDH Show Selectively Reduced NADPH-dependent Catalysis, Similar to Regulatory AB-GAPDH Inhibited by Oxidized ThioredoxinSparla, F., Fermani, S., Falini, G., Zaffagnini, M., Ripamonti, A., Sabatino, P., Pupillo, P., Trost, P.
(2004) J.Mol.Biol. 340: 1025-1037
- PubMed: 15236965
- DOI: 10.1016/j.jmb.2004.06.005
- Primary Citation of Related Structures:
- PubMed Abstract:
- Crystal structure of the non-regulatory A4 isoform of spinach chloroplast glyceraldehyde-3-phosphate dehydrogenase complexed with NADP
Fermani, S.,Ripamonti, A.,Sabatino, P.,Zanotti, G.,Scagliarini, S.,Sparla, F.,Trost, P.,Pupillo, P.
(2001) J.Mol.Biol. 314: 527
- The dual coenzyme specificity of photosynthetic glyceraldehyde-3-phosphate dehydrogenase interpreted by the crystal structure of A4 isoform complexed with NAD
Falini, G.,Fermani, S.,Ripamonti, A.,Sabatino, P.,Sparla, F.,Pupillo, P.,Trost, P.
(2003) Biochemistry 42: 4631
Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher plants uses both NADP(H) and NAD(H) as coenzyme and consists of one (GapA) or two types of subunits (GapA, GapB). AB-GAPDH is regulated in vivo through the action of thioredoxin a ...
Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher plants uses both NADP(H) and NAD(H) as coenzyme and consists of one (GapA) or two types of subunits (GapA, GapB). AB-GAPDH is regulated in vivo through the action of thioredoxin and metabolites, showing higher kinetic preference for NADPH in the light than in darkness due to a specific effect on kcat(NADPH). Previous crystallographic studies on spinach chloroplast A4-GAPDH complexed with NADP or NAD showed that residues Thr33 and Ser188 are involved in NADP over NAD selectivity by interacting with the 2'-phosphate group of NADP. This suggested a possible involvement of these residues in the regulatory mechanism. Mutants of recombinant spinach GapA (A4-GAPDH) with Thr33 or Ser188 replaced by Ala (T33A, S188A and double mutant T33A/S188A) were produced, expressed in Escherichia coli, and compared to wild-type recombinant A4-GAPDH, in terms of crystal structures and kinetic properties. Affinity for NADPH was decreased significantly in all mutants, and kcat(NADPH) was lowered in mutants carrying the substitution of Ser188. NADH-dependent activity was unaffected. The decrease of kcat/Km of the NADPH-dependent reaction in Ser188 mutants resembles the behaviour of AB-GAPDH inhibited by oxidized thioredoxin, as confirmed by steady-state kinetic analysis of native enzyme. A significant expansion of size of the A4-tetramer was observed in the S188A mutant compared to wild-type A4. We conclude that in the absence of interactions between Ser188 and the 2'-phosphate group of NADP, the enzyme structure relaxes to a less compact conformation, which negatively affects the complex catalytic cycle of GADPH. A model based on this concept might be developed to explain the in vivo light-regulation of the GAPDH.
Laboratorio di Fisiologia molecolare delle piante, Dipartimento di Biologia Evoluzionistica Sperimentale, via Irnerio 42, Università di Bologna, I-40126 Bologna, Italy.