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Christopher J Lingle - One of the best experts on this subject based on the ideXlab platform.
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Divalent Cation sensitivity of bk channel activation supports the existence of three distinct binding sites
The Journal of General Physiology, 2005Co-Authors: Xuhui Zeng, Xiaoming Xia, Christopher J LingleAbstract:Mutational analyses have suggested that BK channels are regulated by three distinct Divalent Cation-dependent regulatory mechanisms arising from the cytosolic COOH terminus of the pore-forming α subunit. Two mechanisms account for physiological regulation of BK channels by μM Ca2+. The third may mediate physiological regulation by mM Mg2+. Mutation of five aspartate residues (5D5N) within the so-called Ca2+ bowl removes a portion of a higher affinity Ca2+ dependence, while mutation of D362A/D367A in the first RCK domain also removes some higher affinity Ca2+ dependence. Together, 5D5N and D362A/D367A remove all effects of Ca2+ up through 1 mM while E399A removes a portion of low affinity regulation by Ca2+/Mg2+. If each proposed regulatory effect involves a distinct Divalent Cation binding site, the Divalent Cation selectivity of the actual site that defines each mechanism might differ. By examination of the ability of various Divalent Cations to activate currents in constructs with mutationally altered regulatory mechanisms, here we show that each putative regulatory mechanism exhibits a unique sensitivity to Divalent Cations. Regulation mediated by the Ca2+ bowl can be activated by Ca2+ and Sr2+, while regulation defined by D362/D367 can be activated by Ca2+, Sr2+, and Cd2+. Mn2+, Co2+, and Ni2+ produce little observable effect through the high affinity regulatory mechanisms, while all six Divalent Cations enhance activation through the low affinity mechanism defined by residue E399. Furthermore, each type of mutation affects kinetic properties of BK channels in distinct ways. The Ca2+ bowl mainly accelerates activation of BK channels at low [Ca2+], while the D362/D367-related high affinity site influences both activation and deactivation over the range of 10–300 μM Ca2+. The major kinetic effect of the E399-related low affinity mechanism is to slow deactivation at mM Mg2+ or Ca2+. The results support the view that three distinct Divalent-Cation binding sites mediate regulation of BK channels.
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allosteric regulation of bk channel gating by ca2 and mg2 through a nonselective low affinity Divalent Cation site
The Journal of General Physiology, 2001Co-Authors: Xue Zhang, C R Solaro, Christopher J LingleAbstract:The ability of membrane voltage to activate high conductance, calcium-activated (BK-type) K+ channels is enhanced by cytosolic calcium (Ca2+). Activation is sensitive to a range of [Ca2+] that spans over four orders of magnitude. Here, we examine the activation of BK channels resulting from expression of cloned mouse Slo1 α subunits at [Ca2+] and [Mg2+] up to 100 mM. The half-activation voltage (V0.5) is steeply dependent on [Ca2+] in the micromolar range, but shows a tendency towards saturation over the range of 60–300 μM Ca2+. As [Ca2+] is increased to millimolar levels, the V0.5 is strongly shifted again to more negative potentials. When channels are activated by 300 μM Ca2+, further addition of either mM Ca2+ or mM Mg2+ produces similar negative shifts in steady-state activation. Millimolar Mg2+ also produces shifts of similar magnitude in the complete absence of Ca2+. The ability of millimolar concentrations of Divalent Cations to shift activation is primarily correlated with a slowing of BK current deactivation. At voltages where millimolar elevations in [Ca2+] increase activation rates, addition of 10 mM Mg2+ to 0 Ca2+ produces little effect on activation time course, while markedly slowing deactivation. This suggests that Mg2+ does not participate in Ca2+-dependent steps that influence current activation rate. We conclude that millimolar Mg2+ and Ca2+ concentrations interact with low affinity, relatively nonselective Divalent Cation binding sites that are distinct from higher affinity, Ca2+-selective binding sites that increase current activation rates. A symmetrical model with four independent higher affinity Ca2+ binding steps, four voltage sensors, and four independent lower affinity Ca2+/Mg2+ binding steps describes well the behavior of G-V curves over a range of Ca2+ and Mg2+. The ability of a broad range of [Ca2+] to produce shifts in activation of Slo1 conductance can, therefore, be accounted for by multiple types of Divalent Cation binding sites.
Merlin L Bruening - One of the best experts on this subject based on the ideXlab platform.
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adsorption of polyelectrolyte multilayers imparts high monovalent Divalent Cation selectivity to aliphatic polyamide Cation exchange membranes
Journal of Membrane Science, 2017Co-Authors: Yan Zhu, Maria Misovich, Andriy Yaroshchuk, Muhammad Ahmad, Liu Yang, Merlin L BrueningAbstract:Abstract Nafion membranes coated with polyelectrolyte multilayers (PEMs) exhibit outstanding monovalent/Divalent Cation electrodialysis selectivity in a single-membrane cell. Nevertheless, the high cost of Nafion and the extensive pretreatments required for polyelectrolyte adsorption on this surface may preclude the use of these membranes in many appliCations. This work reports that native aliphatic polyamide Fujifilm type 1 Cation-exchange membranes modified with protonated poly(allylamine) (PAH)/poly (4-styrenesulfonate) (PSS) films also show extremely high K+/Mg2+ Cation selectivities in ED with a single-membrane cell. Even with 0.1 M salt in the source phase, the K+/Mg2+ selectivity is >1000. The very low transfer of Divalent Cations implies that the PEM forms a complete, continuous coating on the smooth Fujifilm surface. Moreover, for a membrane coated on both sides, the PEM on the anode side is responsible for most of the selectivity. However, the current efficiency is only ~0.6 for PAH/PSS-modified Fujifilm or Nafion membranes. Adsorption of highly water-swollen (PDADMAC/PSS)n films on Nafion membranes leads to high K+/Mg2+ and Li+/Co2+ selectivities in ED, and the monovalent Cation current efficiency reaches 0.8.
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coating of nafion membranes with polyelectrolyte multilayers to achieve high monovalent Divalent Cation electrodialysis selectivities
ACS Applied Materials & Interfaces, 2015Co-Authors: Nicholas White, Maria Misovich, Andriy Yaroshchuk, Merlin L BrueningAbstract:Electrodialysis (ED) membranes typically exhibit modest selectivities between monovalent and Divalent ions. This paper reports a dramatic enhancement of the monovalent/Divalent Cation selectivities of Nafion 115 membranes through coating with multilayer poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films. Remarkably, K+/Mg2+ ED selectivities reach values >1000, and similar monovalent/Divalent Cation selectivities occur with feed solutions containing K+ and Ca2+. For comparison, the corresponding K+/Mg2+ selectivity of bare Nafion 115 is only 1.8 ± 0.1. However, with 0.01 M KNO3 and 0.01 M Mg(NO3)2 in the source phase, as the applied current density increases from 1.27 to 2.54 mA cm–2, the K+/Mg2+ selectivities of coated membranes decrease from >1000 to 22. Water-splitting at strongly overlimiting current densities may lead to a local pH increase close to the membrane surface and alter film permeability or allow passage of Mg(OH)x species to decrease selectivity. When the source phase co...
James L Mobley - One of the best experts on this subject based on the ideXlab platform.
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distinct Divalent Cation requirements for integrin mediated cd4 t lymphocyte adhesion to icam 1 fibronectin vcam 1 and invasin
Journal of Immunology, 1993Co-Authors: Yoji Shimizu, James L MobleyAbstract:Integrins are a large family of cell surface receptors that mediate the adhesion of cells to other cells and to components of the extracellular matrix. Various Divalent Cations, particularly Ca2+ and Mn2+, have been shown to modulate the functional activity of many different integrins expressed on a wide variety of cell types. In this study, we have characterized the Divalent Cation requirements for the adhesion of human peripheral CD4+ T cells to four distinct integrin ligands: the alpha 4 beta 1 and alpha 5 beta 1 ligand fibronectin, the alpha 4 beta 1 ligand VCAM-1, the LFA-1 ligand ICAM-1, and the alpha 4 beta 1 bacterial ligand invasin. We find that there are distinct Divalent Cation requirements for T cell adhesion to each of these ligands: 1) Mg2+/EGTA treatment selectively up-regulates T cell adhesion to ICAM-1; 2) Mn2+ coordinately up-regulates adhesion to ICAM-1, fibronectin, and VCAM-1, with a peak response at 100 microM Mn2+; 3) Ca2+ can selectively support adhesion to VCAM-1 induced by activation and inhibit Mn(2+)-dependent adhesion to ICAM-1; and 4) binding to invasin is maximal in the presence of Ca2+, Mg2+, or Mn2+. Furthermore, Divalent Cation modifiCations do not fully up-regulate T cell adhesion to fibronectin, VCAM-1, and ICAM-1, because additional cell activation with phorbol ester treatment can further enhance adhesion in the presence of Mn2+. These results suggest that modifiCation of Divalent Cations may provide a mechanism by which an individual integrin receptor/ligand interaction can be specifically and selectively regulated.
Samuel A. Santoro - One of the best experts on this subject based on the ideXlab platform.
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structural analysis of the alpha 2 integrin i domain procollagenase 1 matrix metalloproteinase 1 interaction
Journal of Biological Chemistry, 2001Co-Authors: Thomas Stricker, Joann Dumin, S K Dickeson, L Chung, William C Parks, Samuel A. SantoroAbstract:Abstract Previous studies have established that ligation of keratinocyte α2β1integrin by type I collagen induces expression of matrix metalloproteinase-1 (MMP-1) and that MMP-1 activity is required for the α2β1 integrin-dependent migration of primary keratinocytes across collagenous matrices. We now present evidence that MMP-1 binds the α2β1integrin via the I domain of the α2 integrin subunit. Using an enzyme-linked immunosorbent assay with purified human MMP-1 and recombinant α2 integrin I domain, we showed that the α2 integrin I domain specifically bound in a Divalent Cation-dependent manner to both the pro and active forms of MMP-1, but not to MMP-3 or MMP-13. Although both the I domain and MMP-1 bind Divalent Cations, MMP-1 bound, in a Divalent Cation-dependent manner, to α2 integrin I domains containing metal ion-dependent adhesion sites motif mutations that prevent Divalent Cation binding to the I domain, demonstrating that the metal ion dependence is a function of MMP-1. Using a series of MMP-1-MMP-3 and MMP-1-MMP-13 chimeras, we determined that both the linker domain and the hemopexin-like domain of MMP-1 were required for optimal binding to the I domain. The α2 integrin/MMP-1 interaction described here extends an emerging paradigm in matrix biology involving anchoring of proteinases to the cell surface to regulate their biological activities.
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contributions of the i and ef hand domains to the Divalent Cation dependent collagen binding activity of the α2β1 integrin
Journal of Biological Chemistry, 1997Co-Authors: Kent S Dickeson, John J Walsh, Samuel A. SantoroAbstract:The alpha2beta1 integrin binds collagen in a Mg2+-dependent manner that is inhibited by Ca2+. Like the intact integrin, purified recombinant proteins containing the alpha2 integrin I domain, either alone or with variable numbers of alpha2 integrin EF hand metal binding sites, bound collagen in a Mg2+-dependent manner, and Ca2+ did not support binding. However, unlike the intact integrin, Ca2+ did not inhibit the Mg2+-dependent binding of any of the fusion proteins to collagen. Binding to collagen was saturable and blocked by the alpha2beta1 function blocking antibody 6F1. Deletional analysis demonstrated that residues present within the amino-terminal 35 amino acids contribute to the 6F1 epitope and are required for Mg2+-dependent collagen binding. The results indicate that the I domain contains a Mg2+ binding site that is essential for collagen binding and that the I domain alone is sufficient for collagen binding. Binding is markedly enhanced in a Divalent Cation-dependent manner by the addition of the first EF hand motif. Mutation of the EF hand to an inactive form completely abrogated the effect. The sites necessary for Ca2+ inhibition are not present within the I domain or the adjacent region containing the three EF hand sites.
Andrew M Scharenberg - One of the best experts on this subject based on the ideXlab platform.
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ltrpc7 is a mg atp regulated Divalent Cation channel required for cell viability
Nature, 2001Co-Authors: Monica J S Nadle, Annelaure Perraud, Meredith C Hermosura, Kazunori Inabe, Qiqi Zhu, Alexande J Stokes, Tomohiro Kurosaki, Jeanpierre Kine, Reinhold Penne, Andrew M ScharenbergAbstract:The molecular mechanisms that regulate basal or background entry of Divalent Cations into mammalian cells are poorly understood. Here we describe the cloning and functional characterization of a Ca2+- and Mg2+-permeable Divalent Cation channel, LTRPC7 (nomenclature compatible with that proposed in ref. 1), a new member of the LTRPC family of putative ion channels. Targeted deletion of LTRPC7 in DT-40 B cells was lethal, indicating that LTRPC7 has a fundamental and nonredundant role in cellular physiology. Electrophysiological analysis of HEK-293 cells overexpressing recombinant LTRPC7 showed large currents regulated by millimolar levels of intracellular Mg·ATP and Mg·GTP with the permeation properties of a voltage-independent Divalent Cation influx pathway. Analysis of several cultured cell types demonstrated small magnesium-nucleotide-regulated metal ion currents (MagNuM) with regulation and permeation properties essentially identical to the large currents observed in cells expressing recombinant LTRPC7. Our data indicate that LTRPC7, by virtue of its sensitivity to physiological Mg·ATP levels, may be involved in a fundamental process that adjusts plasma membrane Divalent Cation fluxes according to the metabolic state of the cell.