INVESTIGADORES
SENN Maria Eugenia
artículos
Título:
Comparative functional features of plant potassium HvHAK1 and HvHAK2 transporters
Autor/es:
MARÍA E. SENN; FRANCISCO RUBIO; MARÍA A. BAÑUELOS; ALONSO RODRÍGUEZ-NAVARRO
Revista:
JOURNAL OF BIOLOGICAL CHEMISTRY
Editorial:
American Society of Biochemistry and Molecular Biology, Inc.
Referencias:
Año: 2001 vol. 276 p. 44563 - 44569
ISSN:
0021-9258
Resumen:
Plant K+ transporters of the HAK family belong to
four rather divergent phylogenetic clusters, although
most of the transporters belong to clusters I or II. A
simple phylogenetic analysis of fungal and plant HAK
transporters suggests that an original HAK gene duplicated
even before fungi and plants diverged, generating
transporters that at present fulfill different functions in
the plant. The HvHAK1 transporter belongs to cluster I
and mediates high-affinity K+ uptake in barley roots,
but no function is known for the cluster II transporter,
HvHAK2, which is not functional in yeast. The function
of HvHAK2 was investigated by constructing HvHAK1-
HAK2 chimeric transporters, which were not functional
even when they included only short fragments of
HvHAK2. Then, amino acids characteristic of cluster II
in the N terminus and in the first transmembrane domain
were introduced into HvHAK1. All of these
changes increased the Rb+ Km, introducing minimal
changes in the Na+ Km, which suggested that HvHAK2 is
a low-affinity, Na+-sensitive K+ transporter. Using a K+-
defective Escherichia coli mutant, we functionally expressed
HvHAK2 and found that the predicted characteristics
were correct, as well as discovering that the
bacterial expression of HvHAK2 is functional at pH 5.5
but not at 7.5. We discuss whether HvHAK2 may be a
tonoplast transporter effective for vacuolar K+ depletion
in K+ starved plants.