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pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions
NBCe1-A is an integral membrane protein that cotransports Na(+) and HCO(3)(-) ions across the basolateral membrane of the proximal tubule. It is essential for maintaining a homeostatic balance of cellular and blood pH. In X-ray diffraction studies, we reported that the cytoplasmic, N-terminal domain...
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Bentham Science Publishers
2012
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3474958/ https://www.ncbi.nlm.nih.gov/pubmed/22316307 http://dx.doi.org/10.2174/092986612802762642 |
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author | Gill, Harindarpal S |
author_facet | Gill, Harindarpal S |
author_sort | Gill, Harindarpal S |
collection | PubMed |
description | NBCe1-A is an integral membrane protein that cotransports Na(+) and HCO(3)(-) ions across the basolateral membrane of the proximal tubule. It is essential for maintaining a homeostatic balance of cellular and blood pH. In X-ray diffraction studies, we reported that the cytoplasmic, N-terminal domain of NBCe1-A (NtNBCe1-A) is a dimer. Here, biophysical measurements show that the dimer is in a concentration-dependent dynamic equilibrium among three additional states in solution that are characterized by its hydrodynamic properties, molar masses, emission spectra, binding properties, and stabilities as a function of pH. Under physiological conditions, dimers are in equilibrium with monomers that are pronounced at low concentration and clusters of molecular masses up to 3-5 times that of a dimer that are pronounced at high concentration. The equilibrium can be influenced so that individual dimers predominate in a taut conformation by lowering the pH. Conversely, dimers begin to relax and disassociate into an increasing population of monomers by elevating the pH. A mechanistic diagram for the inter-conversion of these states is given. The self-associations are further supported by surface plasmon resonance (SPR-Biacore) techniques that illustrate NtNBCe1-A molecules transiently bind with one another. Bicarbonate and bicarbonate-analog bisulfite appear to enhance dimerization and induce a small amount of tetramers. A model is proposed, where the Nt responds to pH or bicarbonate fluctuations inside the cell and plays a role in self-association of entire NBCe1-A molecules in the membrane. |
format | Online Article Text |
id | pubmed-3474958 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2012 |
publisher | Bentham Science Publishers |
record_format | MEDLINE/PubMed |
spelling | pubmed-34749582012-10-22 pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions Gill, Harindarpal S Protein Pept Lett Article NBCe1-A is an integral membrane protein that cotransports Na(+) and HCO(3)(-) ions across the basolateral membrane of the proximal tubule. It is essential for maintaining a homeostatic balance of cellular and blood pH. In X-ray diffraction studies, we reported that the cytoplasmic, N-terminal domain of NBCe1-A (NtNBCe1-A) is a dimer. Here, biophysical measurements show that the dimer is in a concentration-dependent dynamic equilibrium among three additional states in solution that are characterized by its hydrodynamic properties, molar masses, emission spectra, binding properties, and stabilities as a function of pH. Under physiological conditions, dimers are in equilibrium with monomers that are pronounced at low concentration and clusters of molecular masses up to 3-5 times that of a dimer that are pronounced at high concentration. The equilibrium can be influenced so that individual dimers predominate in a taut conformation by lowering the pH. Conversely, dimers begin to relax and disassociate into an increasing population of monomers by elevating the pH. A mechanistic diagram for the inter-conversion of these states is given. The self-associations are further supported by surface plasmon resonance (SPR-Biacore) techniques that illustrate NtNBCe1-A molecules transiently bind with one another. Bicarbonate and bicarbonate-analog bisulfite appear to enhance dimerization and induce a small amount of tetramers. A model is proposed, where the Nt responds to pH or bicarbonate fluctuations inside the cell and plays a role in self-association of entire NBCe1-A molecules in the membrane. Bentham Science Publishers 2012-10 2012-10 /pmc/articles/PMC3474958/ /pubmed/22316307 http://dx.doi.org/10.2174/092986612802762642 Text en © 2012 Bentham Science Publishers http://creativecommons.org/licenses/by/2.5/ This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.5/), which permits unrestrictive use, distribution, and reproduction in any medium, provided the original work is properly cited. |
spellingShingle | Article Gill, Harindarpal S pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title | pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title_full | pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title_fullStr | pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title_full_unstemmed | pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title_short | pH-sensitive Self-associations of the N-terminal Domain of NBCe1-A Suggest a Compact Conformation under Acidic Intracellular Conditions |
title_sort | ph-sensitive self-associations of the n-terminal domain of nbce1-a suggest a compact conformation under acidic intracellular conditions |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3474958/ https://www.ncbi.nlm.nih.gov/pubmed/22316307 http://dx.doi.org/10.2174/092986612802762642 |
work_keys_str_mv | AT gillharindarpals phsensitiveselfassociationsofthenterminaldomainofnbce1asuggestacompactconformationunderacidicintracellularconditions |