HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by de la Horra, C. Articles by Murer, H. Search for Related Content PubMed PubMed Citation Articles by de la Horra, C. Articles by Murer, H.

Amino acids involved in sodium interaction of murine type II Na⁺-P_i cotransporters expressed in Xenopus oocytes

Carmen de la Horra, Nati Hernando, Ian Forster, Jürg Biber and Heini Murer

1. Type IIa and IIb Na⁺-P_i cotransporters are highly conserved proteins expressed in brush border membranes of proximal tubules and small intestine, respectively. The kinetics of IIa and IIb differ significantly: type IIb is saturated at lower concentrations of Na⁺ and P_i.

2. To define the domain responsible for the difference in Na⁺ affinity we constructed several mouse IIa-IIb chimeras as well as site-directed mutagenized cotransporters. P_i uptake activity was determined after injection of cRNAs into Xenopus laevis oocytes.

3. From the chimera experiments we concluded that the domain containing part of the second intracellular loop, the fifth transmembrane domain (TD) and part of the third extracellular loop determines the specific Na⁺ activation properties for both types of cotransporter. Within this domain only a few residues located in the fifth TD are not conserved between type IIa and IIb.

4. Site-directed mutagenesis on non-conserved residues was performed. Substitution of F₄₀₂ of IIa by the corresponding L₄₁₈ from IIb yielded a cotransporter that behaved like the IIb. On the other hand, substitution of the specific L₄₁₈ of IIb by the corresponding F₄₀₂ of IIa produced a cotransporter with a Na⁺ activation similar to IIa. (Single letter amino acid nomenclature is used throughout the paper.)

5. These data suggest that the specific Na⁺ activation properties exhibited by type IIa and type IIb Na⁺-P_i cotransporters are at least in part due to the presence of a specific amino acid (F₄₀₂ in IIa, and L₄₁₈ in IIb) within the fifth TD of the protein.

This article has been cited by other articles:

				A. Bacconi, L. V. Virkki, J. Biber, H. Murer, and I. C. Forster Renouncing electroneutrality is not free of charge: Switching on electrogenicity in a Na+-coupled phosphate cotransporter PNAS, August 30, 2005; 102(35): 12606 - 12611. [Abstract] [Full Text] [PDF]

				S. H. Sugiura and R. P. Ferraris Contributions of different NaPi cotransporter isoforms to dietary regulation of P transport in the pyloric caeca and intestine of rainbow trout J. Exp. Biol., May 15, 2004; 207(12): 2055 - 2064. [Abstract] [Full Text] [PDF]

				C. Graham, P. Nalbant, B. Scholermann, H. Hentschel, R. K. H. Kinne, and A. Werner Characterization of a type IIb sodium-phosphate cotransporter from zebrafish (Danio rerio) kidney Am J Physiol Renal Physiol, April 1, 2003; 284(4): F727 - F736. [Abstract] [Full Text] [PDF]

				H. S. Tenenhouse and H. Murer Disorders of Renal Tubular Phosphate Transport J. Am. Soc. Nephrol., January 1, 2003; 14(1): 240 - 247. [Full Text] [PDF]