title: A Common Signal Patch Drives AP-1 Protein-dependent Golgi Export of Inwardly Rectifying Potassium Channels.
abstract: Nearly all members of the inwardly rectifying potassium (Kir) channel family share a cytoplasmic domain structure that serves as an unusual AP-1 clathrin adaptor-dependent Golgi export signal in one Kir channel, Kir2.1 (KCNJ2), raising the question whether Kir channels share a common Golgi export mechanism. Here we explore this idea, focusing on two structurally and functionally divergent Kir family members, Kir2.3 (KCNJ4) and Kir4.1/5.1 (KCNJ10/16), which have ∼50% amino identity. We found that Golgi export of both channels is blocked upon siRNA-mediated knockdown of the AP-1 γ subunit, as predicted for the common AP-1-dependent trafficking process. A comprehensive mutagenic analysis, guided by homology mapping in atomic resolution models of Kir2.1, Kir2.3, and Kir4.1/5.1, identified a common structure that serves as a recognition site for AP-1 binding and governs Golgi export. Larger than realized from previous studies with Kir2.1, the signal is created by a patch of residues distributed at the confluence of cytoplasmic N and C termini. The signal involves a stretch of hydrophobic residues from the C-terminal region that form a hydrophobic cleft, an adjacent cluster of basic residues within the N terminus, and a potential network of salt bridges that join the N- and C-terminal poles together. Because patch formation and AP-1 binding are dependent on proper folding of the cytoplasmic domains, the signal provides a common quality control mechanism at the Golgi for Kir channels. These findings identify a new proteostatic mechanism that couples protein folding of channels to forward trafficking in the secretory pathway.
authors.affiliation: From the Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201 and.
authors.forename: Xiangming
authors.initials: X
authors.lastname: Li
authors.affiliation: the Department of Biology, The College at Brockport, State University of New York, Brockport, New York 14420-2973.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Ortega
authors.affiliation: From the Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201 and.
authors.forename: Boyoung
authors.initials: B
authors.lastname: Kim
authors.affiliation: From the Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201 and pwelling@som.umaryland.edu.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Welling
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D021382:Protein Sorting Signals / Q000235:genetics; D021381:Protein Transport; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D018808:Transcription Factor AP-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D033961:Adaptor Protein Complex 1; D024661:Potassium Channels, Inwardly Rectifying; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; C121510:SYNRG protein, human; D018808:Transcription Factor AP-1
keywords: adaptor protein; clathrin; intracellular trafficking; potassium channel; protein trafficking (Golgi)