title: Post-translational membrane insertion of tail-anchored transmembrane EF-hand Ca2+ sensor calneurons requires the TRC40/Asna1 protein chaperone.
abstract: Calneuron-1 and -2 are neuronal EF-hand-type calcium sensor proteins that are prominently targeted to trans-Golgi network membranes and impose a calcium threshold at the Golgi for phosphatidylinositol 4-OH kinase IIIβ activation and the regulated local synthesis of phospholipids that are crucial for TGN-to-plasma membrane trafficking. In this study, we show that calneurons are nonclassical type II tail-anchored proteins that are post-translationally inserted into the endoplasmic reticulum membrane via an association of a 23-amino acid-long transmembrane domain (TMD) with the TRC40/Asna1 chaperone complex. Following trafficking to the Golgi, calneurons are probably retained in the TGN because of the length of the TMD and phosphatidylinositol 4-phosphate lipid binding. Both calneurons rapidly self-associate in vitro and in vivo via their TMD and EF-hand containing the N terminus. Although dimerization and potentially multimerization precludes TRC40/Asna1 binding and thereby membrane insertion, we found no evidence for a cytosolic pool of calneurons and could demonstrate that self-association of calneurons is restricted to membrane-inserted protein. The dimerization properties and the fact that they, unlike every other EF-hand calmodulin-like Ca(2+) sensor, are always associated with membranes of the secretory pathway, including vesicles and plasma membrane, suggests a high degree of spatial segregation for physiological target interactions.
authors: Research Group Neuroplasticity, Leibniz-Institute for Neurobiology, 39118 Magdeburg, Germany.
authors: Johannes
authors: J
authors: Hradsky
authors: Vijeta
authors: V
authors: Raghuram
authors: Parameshwar Pasham
authors: PP
authors: Reddy
authors: Gemma
authors: G
authors: Navarro
authors: Mike
authors: M
authors: Hupe
authors: Vicent
authors: V
authors: Casado
authors: Peter J
authors: PJ
authors: McCormick
authors: Yogendra
authors: Y
authors: Sharma
authors: Michael R
authors: MR
authors: Kreutz
authors: Marina
authors: M
authors: Mikhaylova
mesh_terms: D000818:Animals; D053501:Arsenite Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization / Q000502:physiology; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D021601:trans-Golgi Network / Q000235:genetics / Q000378:metabolism*
chemical_list: C428830:CALN1 protein, human; D002147:Calmodulin; C489667:GET3 protein, human; D018832:Molecular Chaperones; D053501:Arsenite Transporting ATPases; D002118:Calcium