Structure and stoichiometry of an accessory subunit TRIP8b interaction with hyperpolarization-activated cyclic nucleotide-gated channels.

Bankston JR, Camp SS, DiMaio F, Lewis AS, Chetkovich DM, Zagotta WN
Proc Natl Acad Sci U S A. 2012 109 (20): 7899-904

PMID: 22550182 · PMCID: PMC3356637 · DOI:10.1073/pnas.1201997109

Ion channels operate in intact tissues as part of large macromolecular complexes that can include cytoskeletal proteins, scaffolding proteins, signaling molecules, and a litany of other molecules. The proteins that make up these complexes can influence the trafficking, localization, and biophysical properties of the channel. TRIP8b (tetratricopetide repeat-containing Rab8b-interacting protein) is a recently discovered accessory subunit of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that contributes to the substantial dendritic localization of HCN channels in many types of neurons. TRIP8b interacts with the carboxyl-terminal region of HCN channels and regulates their cell-surface expression level and cyclic nucleotide dependence. Here we examine the molecular determinants of TRIP8b binding to HCN2 channels. Using a single-molecule fluorescence bleaching method, we found that TRIP8b and HCN2 form an obligate 4:4 complex in intact channels. Fluorescence-detection size-exclusion chromatography and fluorescence anisotropy allowed us to confirm that two different domains in the carboxyl-terminal portion of TRIP8b--the tetratricopepide repeat region and the TRIP8b conserved region--interact with two different regions of the HCN carboxyl-terminal region: the carboxyl-terminal three amino acids (SNL) and the cyclic nucleotide-binding domain, respectively. And finally, using X-ray crystallography, we determined the atomic structure of the tetratricopepide region of TRIP8b in complex with a peptide of the carboxy-terminus of HCN2. Together, these experiments begin to uncover the mechanism for TRIP8b binding and regulation of HCN channels.

MeSH Terms (21)

Animals Chromatography, Gel Crystallography Fluorescence Polarization Genetic Vectors Green Fluorescent Proteins Humans Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels Ion Channels Mice Microscopy, Fluorescence Models, Molecular Multiprotein Complexes Nerve Tissue Proteins Oocytes Patch-Clamp Techniques Potassium Channels Protein Binding Receptors, Cytoplasmic and Nuclear X-Ray Diffraction Xenopus

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