The long-term goal of this project is to define general principles and molecular mechanisms of Aquaporin (AQP) integration, folding and tetrameric assembly in the endoplasmic reticulum (ER) membrane. Aquaporins comprise a conserved family of 6-spanning, homotetrameric membrane proteins that play critical roles in water homeostasis in the kidney, lung, brain and other tissues. The molecular basis of water transport is achieved by the precise arrangement of six transmembrane helices and two half helices in a two-fold inverted symmetry around a monomeric pore. This structure is generated by the coordinated actions of the ribosome and Sec61 translocation machinery. A major unanswered question in this field is how subtle changes in nascent peptide structure influence this machinery to direct unique, and often pathological folding events. Interestingly, closely related AQPs exhibit different native folding pathways that are specified by just three variant residues. In addition, inherited point mutations in AQP2 disrupt folding and thereby cause nephrogenic diabetes insipidus (NDI), a life threatening disease of impaired urinary concentration. AQPs are therefore ideal model substrates for investigating normal and pathological mechanisms of membrane protein biogenesis that are implicated in a growing number of human protein folding disorders. The current proposal will use modified aminoacyl tRNAs to cotranslationally insert photocrosslinking and fluorescent probes into nascent AQP integration intermediates that are kinetically trapped at defined stages of synthesis. This approach provide a powerful new method to determine how the ER translocation machinery coordinates nascent chain folding in lumenal, cytosolic and membrane environments that closely mimic conditions in the cell. With these techniques we will: 1) define the molecular basis responsible for different AQP folding pathways, 2) define precisely how AQP2 folding is disrupted in nephrogenic diabetes insipidus, 3) define the functional and structural basis of AQP tetramerization required for intracellular trafficking. Results of these studies will significantly advance our understanding of AQP biology and improve our general ability to understand folding properties of complex integral membrane proteins. They will also establish a useful platform to investigate how folding is corrupted by inherited mutations, and thereby ultimately facilitate new strategies to treat diverse protein- folding disorders.

Public Health Relevance

Disorders of membrane protein folding represent a rapidly expanding area of medicine that affects tens of thousands of Americans at enormous economic and social cost. Treatments for these disorders have been limited because basic understanding of biological folding pathways remains largely unknown for membrane proteins. This project will use novel biophysical approaches to define when transmembrane segments begin to fold in the context of ER biosynthetic machinery, how they are inserted into the ER membrane, and specific steps at which folding is disrupted by inherited disease- related mutations.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM053457-16
Application #
8499327
Study Section
Membrane Biology and Protein Processing (MBPP)
Program Officer
Wehrle, Janna P
Project Start
1996-08-01
Project End
2014-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
16
Fiscal Year
2013
Total Cost
$316,334
Indirect Cost
$110,922
Name
Oregon Health and Science University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Conti, Brian J; Elferich, Johannes; Yang, Zhongying et al. (2014) Cotranslational folding inhibits translocation from within the ribosome-Sec61 translocon complex. Nat Struct Mol Biol 21:228-35
Matsumura, Yoshihiro; Sakai, Juro; Skach, William R (2013) Endoplasmic reticulum protein quality control is determined by cooperative interactions between Hsp/c70 protein and the CHIP E3 ligase. J Biol Chem 288:31069-79
Kelkar, Devaki A; Khushoo, Amardeep; Yang, Zhongying et al. (2012) Kinetic analysis of ribosome-bound fluorescent proteins reveals an early, stable, cotranslational folding intermediate. J Biol Chem 287:2568-78
Richards, Rebecca; Scholz, Isabel; Powers, Colin et al. (2011) The cytoplasmic domain of rhesus cytomegalovirus Rh178 interrupts translation of major histocompatibility class I leader peptide-containing proteins prior to translocation. J Virol 85:8766-76
Wycisk, Agnes I; Lin, Jiacheng; Loch, Sandra et al. (2011) Epstein-Barr viral BNLF2a protein hijacks the tail-anchored protein insertion machinery to block antigen processing by the transport complex TAP. J Biol Chem 286:41402-12
Pratt, Emily B; Tewson, Paul; Bruederle, Cathrin E et al. (2011) N-terminal transmembrane domain of SUR1 controls gating of Kir6.2 by modulating channel sensitivity to PIP2. J Gen Physiol 137:299-314
Khushoo, Amardeep; Yang, Zhongying; Johnson, Arthur E et al. (2011) Ligand-driven vectorial folding of ribosome-bound human CFTR NBD1. Mol Cell 41:682-92
Devaraneni, Prasanna K; Conti, Brian; Matsumura, Yoshihiro et al. (2011) Stepwise insertion and inversion of a type II signal anchor sequence in the ribosome-Sec61 translocon complex. Cell 146:134-47
Matsumura, Yoshihiro; David, Larry L; Skach, William R (2011) Role of Hsc70 binding cycle in CFTR folding and endoplasmic reticulum-associated degradation. Mol Biol Cell 22:2797-809
Brodsky, Jeffrey L; Skach, William R (2011) Protein folding and quality control in the endoplasmic reticulum: Recent lessons from yeast and mammalian cell systems. Curr Opin Cell Biol 23:464-75

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