Intrasteric inhibition in redox signalling: light activation of NADP-malate dehydrogenase.

摘要: Chloroplast NADP-dependent malate dehydrogenase (NADP-MDH, EC 1.1.1.82) is inactive in the dark and activated light via a reduction of specific disulfides by thiol-disulfide interchange with thioredoxin, reduced photosynthetic electron transfer. Compared to constitutively active NAD-dependent forms, NADP-MDH exhibits two regulatory per subunit, one located an N-terminal extension other C-terminal extension. Convergent information gathered from biochemical, site-directed mutagenesis structural approaches allowed solve almost completely activation mechanism. In oxidized enzyme, pulled back disulfide bridge toward active-site cleft where penultimate glutamate interacts arginines involved substrate binding, thus acting as internal inhibitor obstructing access oxaloacetate. The extensions are at subunit interface area rigidify overall structure dimer. Their thioredoxin triggers conformational change site towards high-activity conformation, whereas expells end site, opening way for substrate.