Structural basis for light activation of a chloroplast enzyme: the structure of sorghum NADP-malate dehydrogenase in its oxidized form.
Some key chloroplast enzymes are activated by light via a ferredoxin-thioredoxin reduction system which reduces disulfide bridges in the enzymes. We describe for the first time the structural basis for the redox activation of a chloroplast enzyme, the NADP-dependent malate dehydrogenase (MDH) from Sorghum vulgare whose structure has been determined and refined at 2.4 A resolution. In addition to the normal structural components of MDHs, the enzyme exhibits extensions at both the N- and C-termini, each of which contains a regulatory disulfide bridge which must be reduced for activation. The N-terminal disulfide motif is inserted in a cleft between the two subunits of the dimer, thereby locking the domains in each subunit. The C-terminal disulfide keeps the C-terminal residues tight to the enzyme surface and blocks access to the active site. Reduction of the N-terminal disulfide would release the stopper between the domains and give the enzyme the necessary flexibility. Simultaneous reduction of the C-terminal disulfide would free the C-terminal residues from binding to the enzyme and make the active site accessible.
Johansson
K
K
Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala.
Ramaswamy
S
S
Saarinen
M
M
Lemaire-Chamley
M
M
Issakidis-Bourguet
E
E
Miginiac-Maslow
M
M
Eklund
H
H
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000201:enzymology*; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004789:Enzyme Activation / Q000235:genetics; D008027:Light; D008291:Malate Dehydrogenase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D050538:Malate Dehydrogenase (NADP+); D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000037:antagonists & inhibitors / Q000737:chemistry; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification
D004220:Disulfides; D010446:Peptide Fragments; D010940:Plant Proteins; D011994:Recombinant Proteins; D008291:Malate Dehydrogenase; D050538:Malate Dehydrogenase (NADP+)