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The metal-ion-dependent adhesion site in the Von Willebrand factor-A domain of α2δ ö subunits is key to trafficking voltage-gated Ca2+ channels.

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Title:	The metal-ion-dependent adhesion site in the Von Willebrand factor-A domain of α2δ ö subunits is key to trafficking voltage-gated Ca²⁺ channels.
Authors:	Canti, C.¹, Nieto-Rostro, M.¹, Foucault, I.¹, Heblich, F.¹, Wratten, J.¹, Richards, M. W.¹, Hendrich, J.¹, Douglas, L.¹, Page, K. M.¹, Davies, A.¹, Doiphin, A. C.¹ a.dolphin@ucl.ac.uk
Source:	Proceedings of the National Academy of Sciences of the United States of America. 8/9/2005, Vol. 102 Issue 32, p11230-11235. 6p.
Subjects:	Adhesion, Adsorption (Chemistry), Cohesion, Abherents, Von Willebrand factor, Blood coagulation factors
Abstract:	All auxiliary α2δ subunits of voltage-gated Ca2+ (Cav) channels contain an extracellular Von Willebrand factor-A (VWA) domain that, in α2δ-1 and -2, has a perfect metal-ion-dependent adhesion site (MIDAS). Modeling of the α2δ-2 VWA domain shows it to be highly likely to bind a divalent cation. Mutating the three key MIDAS residues responsible for divalent cation binding resulted in a MIDAS mutant α2δ-2 subunit that was still processed and trafficked normally when it was expressed alone. However, unlike WT α2δ-2, the MIDAS mutant α2δ-2 subunit did not enhance and, in some cases, further diminished Cav1.2, -2.1, and -2.2 currents coexpressed with β1b by using either Ba2+ or Na+ as a permeant ion. Furthermore, expression of the MIDAS mutant α2δ-2 reduced surface expression and strongly increased the perinuclear retention of Cavα1 subunits at the earliest time at which expression was observed in both Cos-7 and NG108-15 cells. Despite the presence of endogenous α2δ subunits, heterologous expression of α2δ-2 in differentiated NG108-15 cells further enhanced the endogenous high-threshold Ca2+ currents, whereas this enhancement was prevented by the MIDAS mutations. Our results indicate that α2δ subunits normally interact with the Cavα1 subunit early in their maturation, before the appearance of functional plasma membrane channels, and an intact MIDAS motif in the α2δ subunit is required to promote trafficking of the α1 subunit to the plasma membrane by an integrin-like switch. This finding provides evidence for a primary role of a VWA domain in intracellular trafficking of a multimeric complex, in contrast to the more usual roles in binding extracellular ligands in other exofacial VWA domains. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	All auxiliary α2δ subunits of voltage-gated Ca2+ (Cav) channels contain an extracellular Von Willebrand factor-A (VWA) domain that, in α2δ-1 and -2, has a perfect metal-ion-dependent adhesion site (MIDAS). Modeling of the α2δ-2 VWA domain shows it to be highly likely to bind a divalent cation. Mutating the three key MIDAS residues responsible for divalent cation binding resulted in a MIDAS mutant α2δ-2 subunit that was still processed and trafficked normally when it was expressed alone. However, unlike WT α2δ-2, the MIDAS mutant α2δ-2 subunit did not enhance and, in some cases, further diminished Cav1.2, -2.1, and -2.2 currents coexpressed with β1b by using either Ba2+ or Na+ as a permeant ion. Furthermore, expression of the MIDAS mutant α2δ-2 reduced surface expression and strongly increased the perinuclear retention of Cavα1 subunits at the earliest time at which expression was observed in both Cos-7 and NG108-15 cells. Despite the presence of endogenous α2δ subunits, heterologous expression of α2δ-2 in differentiated NG108-15 cells further enhanced the endogenous high-threshold Ca2+ currents, whereas this enhancement was prevented by the MIDAS mutations. Our results indicate that α2δ subunits normally interact with the Cavα1 subunit early in their maturation, before the appearance of functional plasma membrane channels, and an intact MIDAS motif in the α2δ subunit is required to promote trafficking of the α1 subunit to the plasma membrane by an integrin-like switch. This finding provides evidence for a primary role of a VWA domain in intracellular trafficking of a multimeric complex, in contrast to the more usual roles in binding extracellular ligands in other exofacial VWA domains. [ABSTRACT FROM AUTHOR]
ISSN:	00278424
DOI:	10.1073/pnas.0504183102