Determinants of nucleotide-binding selectivity of malic enzyme.
PLoS One
; 6(9): e25312, 2011.
Article
em En
| MEDLINE
| ID: mdl-21980421
ABSTRACT
Malic enzymes have high cofactor selectivity. An isoform-specific distribution of residues 314, 346, 347 and 362 implies that they may play key roles in determining the cofactor specificity. Currently, Glu314, Ser346, Lys347 and Lys362 in human c-NADP-ME were changed to the corresponding residues of human m-NAD(P)-ME (Glu, Lys, Tyr and Gln, respectively) or Ascaris suum m-NAD-ME (Ala, Ile, Asp and His, respectively). Kinetic data demonstrated that the S346K/K347Y/K362Q c-NADP-ME was transformed into a debilitated NADâº-utilizing enzyme, as shown by a severe decrease in catalytic efficiency using NADP⺠as the cofactor without a significant increase in catalysis using NAD⺠as the cofactor. However, the S346K/K347Y/K362H enzyme displayed an enhanced value for k(cat,NAD), suggesting that His at residue 362 may be more beneficial than Gln for NAD⺠binding. Furthermore, the S346I/K347D/K362H mutant had a very large K(m,NADP) value compared to other mutants, suggesting that this mutant exclusively utilizes NAD⺠as its cofactor. Since the S346K/K347Y/K362Q, S346K/K347Y/K362H and S346I/K347D/K362H c-NADP-ME mutants did not show significant reductions in their K(m,NAD) values, the E314A mutation was then introduced into these triple mutants. Comparison of the kinetic parameters of each triple-quadruple mutant pair (for example, S346K/K347Y/K362Q versus E314A/S346K/K347Y/K362Q) revealed that all of the K(m) values for NAD⺠and NADP(+) of the quadruple mutants were significantly decreased, while either k(cat,NAD) or k(cat,NADP) was substantially increased. By adding the E314A mutation to these triple mutant enzymes, the E314A/S346K/K347Y/K362Q, E314A/S346K/K347Y/K362H and E314A/S346I/K347D/K362H c-NADP-ME variants are no longer debilitated but become mainly NADâº-utilizing enzymes by a considerable increase in catalysis using NAD⺠as the cofactor. These results suggest that abolishing the repulsive effect of Glu314 in these quadruple mutants increases the binding affinity of NADâº. Here, we demonstrate that a series of E314A-containing c-NADP-ME quadruple mutants have been changed to NADâº-utilizing enzymes by abrogating NADP⺠binding and increasing NAD⺠binding.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Malato Desidrogenase
Limite:
Humans
Idioma:
En
Ano de publicação:
2011
Tipo de documento:
Article