Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
Substrate interactions of the electroneutral Na+-coupled inorganic phosphate cotransporter (NaPi-IIc).
Ghezzi C, Murer H, Forster IC.
???displayArticle.abstract???
The SLC34 solute carrier family comprises the electrogenic NaPi-IIa/b and the electroneutral NaPi-IIc, which display Na(+) : P(i) cotransport stoichiometries of 3 : 1 and 2 : 1, respectively. We previously proposed that NaPi-IIc lacks one of the three Na(+) interaction sites hypothesised for the electrogenic isoforms, but, unlike NaPi-IIa/b, its substrate binding order is undetermined. By expressing NaPi-IIc in Xenopus oocytes, isotope influx and efflux assays gave results consistent with Na(+) being the first and last substrate to bind. To further investigate substrate interactions, we applied a fluorometry-based technique that uses site-specific labelling with a fluorophore to characterize substrate-induced conformational changes. A novel Cys was introduced in the third extracellular loop of NaPi-IIc that could be labelled with a reporter fluorophore (MTS-TAMRA). Although labelling resulted in suppression of cotransport as previously reported for the electrogenic isoforms, changes in fluorescence were induced by changes in extracellular Na(+) concentration in the absence of P(i) and by changes in extracellular P(i) concentration in presence of Na(+). These data, combined with (32)P uptake data, also support a binding scheme in which Na(+) is the first substrate to interact. Moreover, the apparent P(i) affinity from fluorometry agreed with that from (32)P uptake, confirming the applicability of the fluorometric technique for kinetic studies of electroneutral carriers. Analysis of the fluorescence data showed that like the electrogenic NaPi-IIb, 2 Na(+) ions interact cooperatively with NaPi-IIc before P(i) binding, which implies that only one of these is translocated. This result provides compelling evidence that SLC34 proteins share common motifs for substrate interaction and that cotransport and substrate binding stoichiometries are not necessarily equivalent.
Andrini,
The leak mode of type II Na(+)-P(i) cotransporters.
2008, Pubmed,
Xenbase
Andrini,
The leak mode of type II Na(+)-P(i) cotransporters.
2008,
Pubmed
,
Xenbase Bacconi,
Renouncing electroneutrality is not free of charge: switching on electrogenicity in a Na+-coupled phosphate cotransporter.
2005,
Pubmed
,
Xenbase Beck,
Targeted inactivation of Npt2 in mice leads to severe renal phosphate wasting, hypercalciuria, and skeletal abnormalities.
1998,
Pubmed Béliveau,
Kinetic model for phosphate transport in renal brush-border membranes.
1988,
Pubmed Bergwitz,
SLC34A3 mutations in patients with hereditary hypophosphatemic rickets with hypercalciuria predict a key role for the sodium-phosphate cotransporter NaPi-IIc in maintaining phosphate homeostasis.
2006,
Pubmed Berteloot,
Kinetic mechanism of Na+ -glucose cotransport through the rabbit intestinal SGLT1 protein.
2003,
Pubmed Busch,
Properties of electrogenic Pi transport by a human renal brush border Na+/Pi transporter.
1995,
Pubmed
,
Xenbase Cha,
Fluorescence techniques for studying cloned channels and transporters expressed in Xenopus oocytes.
1998,
Pubmed
,
Xenbase Drummond,
Reporting ethical matters in the Journal of Physiology: standards and advice.
2009,
Pubmed Ehnes,
Structure-function relations of the first and fourth predicted extracellular linkers of the type IIa Na+/Pi cotransporter: I. Cysteine scanning mutagenesis.
2004,
Pubmed
,
Xenbase Eskandari,
Remarkable commonalities of electrogenic and electroneutral Na+-phosphate cotransporters.
2009,
Pubmed
,
Xenbase Forster,
Electrophysiological characterization of the flounder type II Na+/Pi cotransporter (NaPi-5) expressed in Xenopus laevis oocytes.
1997,
Pubmed
,
Xenbase Forster,
Proton-sensitive transitions of renal type II Na(+)-coupled phosphate cotransporter kinetics.
2000,
Pubmed
,
Xenbase Forster,
Forging the link between structure and function of electrogenic cotransporters: the renal type IIa Na+/Pi cotransporter as a case study.
2002,
Pubmed Forster,
The voltage dependence of a cloned mammalian renal type II Na+/Pi cotransporter (NaPi-2).
1998,
Pubmed
,
Xenbase Forster,
Stoichiometry and Na+ binding cooperativity of rat and flounder renal type II Na+-Pi cotransporters.
1999,
Pubmed
,
Xenbase Hilfiker,
Characterization of a murine type II sodium-phosphate cotransporter expressed in mammalian small intestine.
1998,
Pubmed
,
Xenbase Jaureguiberry,
A novel missense mutation in SLC34A3 that causes hereditary hypophosphatemic rickets with hypercalciuria in humans identifies threonine 137 as an important determinant of sodium-phosphate cotransport in NaPi-IIc.
2008,
Pubmed
,
Xenbase Karlin,
Substituted-cysteine accessibility method.
1998,
Pubmed Köhler,
Transport function of the renal type IIa Na+/P(i) cotransporter is codetermined by residues in two opposing linker regions.
2002,
Pubmed
,
Xenbase Lambert,
Cysteine mutagenesis reveals novel structure-function features within the predicted third extracellular loop of the type IIa Na(+)/P(i) cotransporter.
2001,
Pubmed
,
Xenbase Lambert,
Properties of the mutant Ser-460-Cys implicate this site in a functionally important region of the type IIa Na(+)/P(i) cotransporter protein.
1999,
Pubmed
,
Xenbase Lester,
Permeation properties of neurotransmitter transporters.
1994,
Pubmed Magagnin,
Expression cloning of human and rat renal cortex Na/Pi cotransport.
1993,
Pubmed
,
Xenbase Murer,
The sodium phosphate cotransporter family SLC34.
2004,
Pubmed Rudnick,
Serotonin transporters--structure and function.
2006,
Pubmed Segawa,
Growth-related renal type II Na/Pi cotransporter.
2002,
Pubmed
,
Xenbase Shi,
The mechanism of a neurotransmitter:sodium symporter--inward release of Na+ and substrate is triggered by substrate in a second binding site.
2008,
Pubmed Szczepanska-Konkel,
Phosphonocarboxylic acids as specific inhibitors of Na+-dependent transport of phosphate across renal brush border membrane.
1986,
Pubmed Turner,
Sodium-dependent sulfate transport in renal outer cortical brush border membrane vesicles.
1984,
Pubmed Turner,
Kinetic analysis of a family of cotransport models.
1981,
Pubmed Turner,
Quantitative studies of cotransport systems: models and vesicles.
1983,
Pubmed Virkki,
Substrate interactions in the human type IIa sodium-phosphate cotransporter (NaPi-IIa).
2005,
Pubmed
,
Xenbase Virkki,
Phosphate transporters: a tale of two solute carrier families.
2007,
Pubmed Virkki,
Functionally important residues in the predicted 3(rd) transmembrane domain of the type IIa sodium-phosphate co-transporter (NaPi-IIa).
2005,
Pubmed
,
Xenbase Virkki,
Voltage clamp fluorometric measurements on a type II Na+-coupled Pi cotransporter: shedding light on substrate binding order.
2006,
Pubmed
,
Xenbase Virkki,
Mapping conformational changes of a type IIb Na+/Pi cotransporter by voltage clamp fluorometry.
2006,
Pubmed
,
Xenbase Zeuthen,
Mobility of ions, sugar, and water in the cytoplasm of Xenopus oocytes expressing Na(+)-coupled sugar transporters (SGLT1).
2002,
Pubmed
,
Xenbase
