Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
2004-10-26
pubmed:abstractText
The putative first intracellular and third extracellular linkers are known to play important roles in defining the transport properties of the type IIa Na+-coupled phosphate cotransporter (Kohler, K., I.C. Forster, G. Stange, J. Biber, and H. Murer. 2002b. J. Gen. Physiol. 120:693-705). To investigate whether other stretches that link predicted transmembrane domains are also involved, the substituted cysteine accessibility method (SCAM) was applied to sites in the predicted first and fourth extracellular linkers (ECL-1 and ECL-4). Mutants based on the wild-type (WT) backbone, with substituted novel cysteines, were expressed in Xenopus oocytes, and their function was assayed by isotope uptake and electrophysiology. Functionally important sites were identified in both linkers by exposing cells to membrane permeant and impermeant methanethiosulfonate (MTS) reagents. The cysteine modification reaction rates for sites in ECL-1 were faster than those in ECL-4, which suggested that the latter were less accessible from the extracellular medium. Generally, a finite cotransport activity remained at the end of the modification reaction. The change in activity was due to altered voltage-dependent kinetics of the Pi-dependent current. For example, cys substitution at Gly-134 in ECL-1 resulted in rate-limiting, voltage-independent cotransport activity for V < or = -80 mV, whereas the WT exhibited a linear voltage dependency. After cys modification, this mutant displayed a supralinear voltage dependency in the same voltage range. The opposite behavior was documented for cys substitution at Met-533 in ECL-4. Modification of cysteines at two other sites in ECL-1 (Ile-136 and Phe-137) also resulted in supralinear voltage dependencies for hyperpolarizing potentials. Taken together, these findings suggest that ECL-1 and ECL-4 may not directly form part of the transport pathway, but specific sites in these linkers can interact directly or indirectly with parts of NaPi-IIa that undergo voltage-dependent conformational changes and thereby influence the voltage dependency of cotransport.
pubmed:commentsCorrections
http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-10198426, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-10370077, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-10532962, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-10859311, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-10926678, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11015617, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11058600, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11382804, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11483994, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11880330, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-11880379, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-12015317, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-12379267, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-12407080, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-12517995, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-12739158, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-14561747, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-15504899, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-1695629, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-7515582, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-8063719, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-8327470, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-8567640, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-8938712, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-9063896, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-9398318, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-9636229, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-9649580, http://linkedlifedata.com/resource/pubmed/commentcorrection/15504898-9711606
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0022-1295
pubmed:author
pubmed:issnType
Print
pubmed:volume
124
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
475-88
pubmed:dateRevised
2009-11-18
pubmed:meshHeading
pubmed-meshheading:15504898-Amino Acid Sequence, pubmed-meshheading:15504898-Animals, pubmed-meshheading:15504898-Cell Membrane, pubmed-meshheading:15504898-Cells, Cultured, pubmed-meshheading:15504898-Cysteine, pubmed-meshheading:15504898-Dose-Response Relationship, Drug, pubmed-meshheading:15504898-Extracellular Fluid, pubmed-meshheading:15504898-Membrane Potentials, pubmed-meshheading:15504898-Mesylates, pubmed-meshheading:15504898-Molecular Sequence Data, pubmed-meshheading:15504898-Mutagenesis, Site-Directed, pubmed-meshheading:15504898-Oocytes, pubmed-meshheading:15504898-Phosphates, pubmed-meshheading:15504898-Protein Subunits, pubmed-meshheading:15504898-Recombinant Proteins, pubmed-meshheading:15504898-Sodium-Phosphate Cotransporter Proteins, pubmed-meshheading:15504898-Structure-Activity Relationship, pubmed-meshheading:15504898-Symporters, pubmed-meshheading:15504898-Xenopus laevis
pubmed:year
2004
pubmed:articleTitle
Structure-function relations of the first and fourth predicted extracellular linkers of the type IIa Na+/Pi cotransporter: I. Cysteine scanning mutagenesis.
pubmed:affiliation
Physiologisches Institut, Universität Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, Non-U.S. Gov't