In this competitive revision of R01GM105993, a new aim is introduced to use camelid variable heavy chain antibody domains (nanobodies) as structural scaffolds and functional probes to investigate the interaction between Ric-8A and Gai1. R01GM105993 funds research to understand how G proteins are activated in the cytoplasm of the cell by a protein factor called Ric-8A. Heterotrimeric G proteins modulate cell metabolism, secretion, electrical conductivity, gene transcription, cell division and cellular motility, and therefore are essential to life in the domain of eukaryotes to which humans belong. Misregulation of G proteins is associated with cancer and a range of other diseases of relevance to general medicine. While most processes controlled by heterotrimeric G proteins occur at cell membranes, recent research has shown that G alpha subunits (Ga) also control certain events in cell cytoplasm. Important among these is asymmetric cell division, which is essential for embryonic development. Ric-8A is critical regulator of Ga in this process. Ric-8A is a Guanine nucleotide Exchange Factor (GEF) that activates Ga by catalyzing the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) at the active site of Ga. The intermediate in this reaction is the nucleotide-free Ga:Ric-8A complex. Describing the structural changes that occur when Ric-8A binds to Ga*GDP is key to understanding how Ric-8A activates Ga. Ric-8A is also a chaperone that promotes proper folding of Ga in cells. The first three aims of R01GM105993 address the structure and the dynamic behavior of the Ric-8A:Gai1 complex, and the structural changes in Ga and Ric-8A that accompany its formation. In these aims, Double Electron-Electron Resonance (DEER) spectroscopy, Hydrogen-Deuterium eXchange coupled with Mass Spectrometry (HDX-MS) and single molecule Frster Resonance Energy Transfer (smFRET) experiments will be conducted to probe changes in Gai1 and Ric-8A structure and dynamics. The new aim is to use nanobodies to stabilize discrete structural states of the Ric-8A:Gai1 complex to render them amenable to crystallization and structure determination by X-ray crystallography. Nanobodies that alter the GEF or chaperone activity of Ric-8A will be used to identify functional sites in Ric-8A and Ga using HDX-MS. DEER and smFRET will be used to determine whether nanobodies that impair or enhance Ric-8A activity either attenuate or amplify global structural changes or protein dynamics.

Public Health Relevance

Normal human development requires that events during embryogenesis are tightly controlled, and that physiological processes throughout the body are properly regulated. Molecules called G proteins control both. This research will discover, at the molecular level, how G proteins are themselves regulated by a recently characterized protein molecule called Ric-8. This work will generate fundamental knowledge that will aid in understanding a regulatory process that is essential to life and that is disrupted in many diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
3R01GM105993-03S1
Application #
8960270
Study Section
Molecular and Integrative Signal Transduction Study Section (MIST)
Program Officer
Flicker, Paula F
Project Start
2013-04-01
Project End
2017-02-28
Budget Start
2015-03-01
Budget End
2016-02-29
Support Year
3
Fiscal Year
2015
Total Cost
$121,389
Indirect Cost
$29,914
Name
University of Montana
Department
Type
Organized Research Units
DUNS #
010379790
City
Missoula
State
MT
Country
United States
Zip Code
59812
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Kant, Ravi; Zeng, Baisen; Thomas, Celestine J et al. (2016) Ric-8A, a G protein chaperone with nucleotide exchange activity induces long-range secondary structure changes in G?. Elife 5:
Sprang, Stephen R (2016) Invited review: Activation of G proteins by GTP and the mechanism of G?-catalyzed GTP hydrolysis. Biopolymers 105:449-62
Van Eps, Ned; Thomas, Celestine J; Hubbell, Wayne L et al. (2015) The guanine nucleotide exchange factor Ric-8A induces domain separation and Ras domain plasticity in G?i1. Proc Natl Acad Sci U S A 112:1404-9
Sprang, Stephen R (2013) An acid test for g proteins. Mol Cell 51:405-6
Chan, Puiyee; Thomas, Celestine J; Sprang, Stephen R et al. (2013) Molecular chaperoning function of Ric-8 is to fold nascent heterotrimeric G protein ? subunits. Proc Natl Acad Sci U S A 110:3794-9