First published online June 12, 2003; 10.1104/pp.103.020560
Plant Physiology 132:1353-1361 (2003)
© 2003 American Society of Plant Biologists
CELL BIOLOGY AND SIGNAL TRANSDUCTION
Plants Do It Differently. A New Basis for Potassium/Sodium Selectivity in the Pore of an Ion Channel1
Bao-Guang Hua2,
Richard W. Mercier,
Qiang Leng3 and
Gerald A. Berkowitz*
Agricultural Biotechnology Laboratory, Department of Plant Science, 1390
Storrs Road U–4163, University of Connecticut, Storrs, Connecticut
06269–4163
Understanding of the molecular architecture necessary for selective
K+ permeation through the pore of ion channels is based primarily
on analysis of the crystal structure of the bacterial K+ channel
KcsA, and structure:function studies of cloned animal K+ channels.
Little is known about the conduction properties of a large family of plant
proteins with structural similarities to cloned animal cyclic nucleotide-gated
channels (CNGCs). Animal CNGCs are nonselective cation channels that do not
discriminate between Na+ and K+ permeation. These
channels all have the same triplet of amino acids in the channel pore ion
selectivity filter, and this sequence is different from that of the
selectivity filter found in K+-selective channels. Plant CNGCs have
unique pore selectivity filters; unlike those found in any other family of
channels. At present, the significance of the unique pore selectivity filters
of plant CNGCs, with regard to discrimination between Na+ and
K+ permeation is unresolved. Here, we present an
electrophysiological analysis of several members of this protein family;
identifying the first cloned plant channel (AtCNGC1) that conducts
Na+. Another member of this ion channel family (AtCNGC2) is shown
to have a selectivity filter that provides a heretofore unknown molecular
basis for discrimination between K+ and Na+ permeation.
Specific amino acids within the AtCNGC2 pore selectivity filter (Asn-416,
Asp-417) are demonstrated to facilitate K+ over Na+
conductance. The selectivity filter of AtCNGC2 represents an alternative
mechanism to the well-known GYG amino acid triplet of K+ channels
that has been identified as the critical basis for K+ over
Na+ permeation through the pore of ion channels.
Article, publication date, and citation information can be found at
www.plantphysiol.org/cgi/doi/10.1104/pp.103.020560.
1 This work was supported by the National Science Foundation (grant no.
MCB–0090675 to G.A.B.). This is a publication from the Storrs
Agricultural Experiment Station.
2 Present address: Department of Molecular Biotechnology, Beijing
Agricultural College, No. 7 Beinong Rd, Shahe, Changping, Beijing City, China
102206.
3 Present address: Yale School of Medicine, Department of Cellular and
Molecular Physiology, 333 Cedar Street, B121–SHM, New Haven, CT
06520.
*
Corresponding author; e-mail
gerald.berkowitz{at}uconn.edu;
fax 860–486–0534.
Received January 20, 2003;
returned for revision February 12, 2003;
accepted April 2, 2003.
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