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2017 ; 114
(5
): 1009-1014
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Tuning the ion selectivity of two-pore channels
#MMPMID28096396
Guo J
; Zeng W
; Jiang Y
Proc Natl Acad Sci U S A
2017[Jan]; 114
(5
): 1009-1014
PMID28096396
show ga
Organellar two-pore channels (TPCs) contain two copies of a Shaker-like
six-transmembrane (6-TM) domain in each subunit and are ubiquitously expressed in
plants and animals. Interestingly, plant and animal TPCs share high sequence
similarity in the filter region, yet exhibit drastically different ion
selectivity. Plant TPC1 functions as a nonselective cation channel on the vacuole
membrane, whereas mammalian TPC channels have been shown to be endo/lysosomal
Na(+)-selective or Ca(2+)-release channels. In this study, we performed
systematic characterization of the ion selectivity of TPC1 from Arabidopsis
thaliana (AtTPC1) and compared its selectivity with the selectivity of human TPC2
(HsTPC2). We demonstrate that AtTPC1 is selective for Ca(2+) over Na(+), but
nonselective among monovalent cations (Li(+), Na(+), and K(+)). Our results also
confirm that HsTPC2 is a Na(+)-selective channel activated by
phosphatidylinositol 3,5-bisphosphate. Guided by our recent structure of AtTPC1,
we converted AtTPC1 to a Na(+)-selective channel by mimicking the selectivity
filter of HsTPC2 and identified key residues in the TPC filters that
differentiate the selectivity between AtTPC1 and HsTPC2. Furthermore, the
structure of the Na(+)-selective AtTPC1 mutant elucidates the structural basis
for Na(+) selectivity in mammalian TPCs.
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