文章基本信息

标题：The α2δ subunits of voltage-gated calcium channels form GPI-anchored proteins, a posttranslational modification essential for function
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作者：Anthony Davies ; Ivan Kadurin ; Anita Alvarez-Laviada 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2010
卷号：107
期号：4
页码：1654-1659
DOI：10.1073/pnas.0908735107
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Voltage-gated calcium channels are thought to exist in the plasma membrane as heteromeric proteins, in which the {alpha}1 subunit is associated with two auxiliary subunits, the intracellular {beta} subunit and the {alpha}2{delta} subunit; both of these subunits influence the trafficking and properties of CaV1 and CaV2 channels. The {alpha}2{delta} subunits have been described as type I transmembrane proteins, because they have an N-terminal signal peptide and a C-terminal hydrophobic and potentially transmembrane region. However, because they have very short C-terminal cytoplasmic domains, we hypothesized that the {alpha}2{delta} proteins might be associated with the plasma membrane through a glycosylphosphatidylinositol (GPI) anchor attached to {delta} rather than a transmembrane domain. Here, we provide biochemical, immunocytochemical, and mutational evidence to show that all of the {alpha}2{delta} subunits studied, {alpha}2{delta}-1, {alpha}2{delta}-2, and {alpha}2{delta}-3, show all of the properties expected of GPI-anchored proteins, both when heterologously expressed and in native tissues. They are substrates for prokaryotic phosphatidylinositol-phospholipase C (PI-PLC) and trypanosomal GPI-PLC, which release the {alpha}2{delta} proteins from membranes and intact cells and expose a cross-reacting determinant epitope. PI-PLC does not affect control transmembrane or membrane-associated proteins. Furthermore, mutation of the predicted GPI-anchor sites markedly reduced plasma membrane and detergent-resistant membrane localization of {alpha}2{delta} subunits. We also show that GPI anchoring of {alpha}2{delta} subunits is necessary for their function to enhance calcium currents, and PI-PLC treatment only reduces calcium current density when {alpha}2{delta} subunits are coexpressed. In conclusion, this study redefines our understanding of {alpha}2{delta} subunits, both in terms of their role in calcium-channel function and other roles in synaptogenesis.
关键词：lipid raft ; posttranslational ; electrophysiology ; immunocytochemistry