CEFOBI   05405
CENTRO DE ESTUDIOS FOTOSINTETICOS Y BIOQUIMICOS
Unidad Ejecutora - UE
capítulos de libros
Título:
Structure-function relationship studies of the four Arabidopsis thaliana NADP-malic enzyme isoforms
Autor/es:
GERRARD WHEELER, M. C.; ARIAS, C. L.; MAURINO, V. G.; FLÜGGE, U. I.; ANDREO, C. S.; DRINCOVICH, M. F.
Libro:
Photosynthesis. Energy from the sun
Editorial:
Allen, Grantt and Osmond, eds. Springer
Referencias:
Año: 2008; p. 965 - 969
Resumen:
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The Arabidopsis thaliana genome contains four genes encoding
NADP-malic enzymes (NADP-ME1−4). NADP-ME4 is localized to plastids
whereas the other three isoforms are cytosolic. NADP-ME2 and −4 are
constitutively expressed in mature organs, while NADP-ME1 and −3 are
restricted to secondary roots and to trichomes and pollen,
respectively. Although the four isoforms share a high degree of
identity, the recombinant NADP-ME1 to 4 show well-distinct kinetic and
structural properties. NADP-ME2 exhibits the highest specific activity,
while NADP-ME3 and −4 present the highest catalytic efficiency for NADP
and malate, respectively. When analyzing the activity of each isoform
in the presence of possible metabolic effectors, the results obtained
indicate that NADP-ME2 is the most highly regulated isoform, especially
by activation. The four isoforms behave differently in terms of
reversibility, presenting NADP-ME4 the highest ratio between the
reverse carboxylation and reduction of pyruvate to the forward
reaction. In order to identify residues or segments of the primary
structure of each NADPME isoform that could be involved in the
differences in kinetic and regulatory properties among the isoforms,
NADP-ME2 mutants and deletions were constructed and analysed. The
results obtained show that Arg115 is involved in fumarate activation,
while the regions involved in aspartate and CoA modulation are located
at the amino-terminal part of the protein. On overall, these studies
show that minimal structural changes are responsible for the different
kinetic behaviour of each AtNADP-ME isoform.