1civ
From Proteopedia
|
CHLOROPLAST NADP-DEPENDENT MALATE DEHYDROGENASE FROM FLAVERIA BIDENTIS
Overview
BACKGROUND: NADP-dependent malate dehydrogenase (EC 1.1.1.82) is a, light-activated chloroplast enzyme that functions in the C4 pathway of, photosynthesis. The light regulation is believed to be mediated in vivo by, thioredoxin-catalyzed reduction and re-oxidation of cystine residues. The, rates of reversible activation and inactivation of the enzyme are strongly, influenced by the coenzyme substrates that seem to ultimately determine, the steady-state extent of activation in vivo. RESULTS: The X-ray, structure of the inactive, oxidized enzyme was determined at 2.8 A, resolution. The core structure is homologous to AND-dependent malate, dehydrogenases. Two surface-exposed and thioredoxin-accessible disulfide, bonds are present, one in the N-terminal extension and the other in the, C-terminal extension. The C-terminal peptide of the inactive, oxidized, enzyme is constrained by its disulfide bond to fold into the active site, over NADP+, hydrogen bonding to the catalytic His225 as well as, obstructing access of the C4 acid substrate. Two loops flanking the active, site, termed the Arg2 and Trp loops, that contain the C4 acid substrate, binding residues are prevented from closing by the C-terminal extension., CONCLUSIONS: The structure explains the role of the C-terminal extension, in inhibiting activity. The negative C terminus will interact more, strongly with the positively charged nicotinamide of NADP+ than NADPH, explaining why the coenzyme-binding affinities of the enzyme differ so, markedly from those of all other homologous alpha-hydroxy acid, dehydrogenases. NADP+ may also slow dissociation of the C terminus upon, reduction, providing a mechanism for the inhibition of activation by NADP+, but not NADPH.
About this Structure
1CIV is a Single protein structure of sequence from Flaveria bidentis with NAP as ligand. Active as Malate dehydrogenase (NADP(+)), with EC number 1.1.1.82 Full crystallographic information is available from OCA.
Reference
Chloroplast NADP-malate dehydrogenase: structural basis of light-dependent regulation of activity by thiol oxidation and reduction., Carr PD, Verger D, Ashton AR, Ollis DL, Structure. 1999 Apr 15;7(4):461-75. PMID:10196131
Page seeded by OCA on Tue Nov 20 12:30:03 2007
