title: Crystal structure of the non-regulatory A(4 )isoform of spinach chloroplast glyceraldehyde-3-phosphate dehydrogenase complexed with NADP.
abstract: Here, we report the first crystal structure of a photosynthetic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) complexed with NADP. The enzyme, purified from spinach chloroplasts, is constituted of a single type of subunit (A) arranged in homotetramers. It shows non-regulated NADP-dependent and NAD-dependent activities, with a preference for NADP. The structure has been solved to 3.0 A resolution by molecular replacement. The crystals belong to space group C222 with three monomers in the asymmetric unit. One of the three monomers generates a tetramer using the space group 222 point symmetry and a very similar tetramer is generated by the other two monomers, related by a non-crystallographic symmetry, using a crystallographic 2-fold axis. The protein reveals a large structural homology with known GAPDHs both in the cofactor-binding domain and in regions of the catalytic domain. Like all other GAPDHs investigated so far, the A(4)-GAPDH belongs to the Rossmann fold family of dehydrogenases. However, unlike most dehydrogenases of this family, the adenosine 2'-phosphate group of NADP does not form a salt-bridge with any positively charged residue in its surroundings, being instead set in place by hydrogen bonds with a threonine residue belonging to the Rossmann fold and a serine residue located in the S-loop of a symmetry-related monomer. While increasing our knowledge of an important photosynthetic enzyme, these results contribute to a general understanding of NADP versus NAD recognition in pyridine nucleotide-dependent enzymes. Although the overall structure of A(4)-GAPDH is similar to that of the cytosolic GAPDH from bacteria and eukaryotes, the chloroplast tetramer is peculiar, in that it can actually be considered a dimer of dimers, since monomers are bound in pairs by a disulphide bridge formed across Cys200 residues. This bridge is not found in other cytosolic or chloroplast GAPDHs from animals, bacteria, or plants other than spinach.
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, Bologna, 40126, Italia. fermani@ciam.unibo.it
authors.forename: S
authors.initials: S
authors.lastname: Fermani
authors.forename: A
authors.initials: A
authors.lastname: Ripamonti
authors.forename: P
authors.initials: P
authors.lastname: Sabatino
authors.forename: G
authors.initials: G
authors.lastname: Zanotti
authors.forename: S
authors.initials: S
authors.lastname: Scagliarini
authors.forename: F
authors.initials: F
authors.lastname: Sparla
authors.forename: P
authors.initials: P
authors.lastname: Trost
authors.forename: P
authors.initials: P
authors.lastname: Pupillo
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / Q000737:chemistry* / Q000378:metabolism*; D006860:Hydrogen Bonding; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D018724:Spinacia oleracea / Q000201:enzymology*; D055672:Static Electricity; D013431:Sulfates / Q000378:metabolism; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D013431:Sulfates; D014867:Water; D009249:NADP; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+)