Reference "Structural basis for light activation of a chloroplast enzyme: the structure of sorghum NADP-malate dehydrogenase in its oxidized form"

Reference ID

9027

Title

Structural basis for light activation of a chloroplast enzyme: the structure of sorghum NADP-malate dehydrogenase in its oxidized form

Source

Biochemistry (John Wiley & Sons), 1999, vol. 38, pp. 4319-4326

Authors (7)

Johansson-K	Ramaswamy-S
Saarinen-M	Lemaire-Chamley-M
Issakidis-Bourguet-E	Miginiac-Maslow-M
Eklund-H

Abstract

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.