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Updated: Feb 2, 2026
Interview: Protein Folding and Studies of Neurodegenerative Diseases
Published on: July 16, 2008
Folding of Gα Subunits: Implications for Disease States
Matthew Najor1, Brian D Leverson1, Jesse L Goossens1
1Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States.
Abstract:
G-proteins play a central role in signal transduction by fluctuating between "on" and "off" phases that are determined by a conformational change. cAMP is a secondary messenger whose formation is inhibited or stimulated by activated Giα1 or Gsα subunit. We used tryptophan fluorescence, UV/vis spectrophotometry, and circular dichroism to probe distinct structural features within active and inactive conformations from wild-type and tryptophan mutants of Giα1 and Gsα. For all proteins studied, we found that the active conformations were more stable than the inactive conformations, and upon refolding from higher temperatures, activated wild-type subunits recovered significantly more native structure. We also observed that the wild-type subunits partially regained the ability to bind nucleotide. The increased compactness observed upon activation was consistent with the calculated decrease in solvent accessible surface area for wild-type Giα1. We found that as the temperature increased, Gα subunits, which are known to be rich in α-helices, converted to proteins with increased content of β-sheets and random coil. For active conformations from wild-type and tryptophan mutants of Giα1, melting temperatures indicated that denaturation starts around hydrophobic tryptophan microenvironments and then radiates toward tyrosine residues at the surface, followed by alteration of the secondary structure. For Gsα, however, disruption of secondary structure preceded unfolding around tyrosine residues. In the active conformations, a π-cation interaction between essential arginine and tryptophan residues, which was characterized by a fluorescence-measured red shift and modeled by molecular dynamics, was also shown to be a contributor to the stability of Gα subunits. The folding properties of Gα subunits reported here are discussed in the context of diseases associated to G-proteins.
Insights
Activated G-protein subunits (Giα1 and Gsα) are more stable and compact than inactive forms. Understanding their folding properties is crucial for G-protein-related diseases.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- G-proteins are key signal transducers, cycling between active and inactive states via conformational changes.
- Giα1 and Gsα subunits modulate cyclic AMP (cAMP) levels, impacting cellular signaling.
- Understanding the structural dynamics of G-protein subunits is vital for deciphering their function and dysfunction in disease.
Purpose of the Study:
- To investigate the structural differences between active and inactive conformations of Giα1 and Gsα subunits.
- To explore the folding properties and stability of wild-type and mutant G-protein subunits using biophysical techniques.
- To elucidate the role of specific residues and interactions in G-protein subunit stability.
Main Methods:
- Tryptophan fluorescence spectroscopy to probe protein structure and environment.
- UV/vis spectrophotometry to assess protein concentration and conformational changes.
- Circular dichroism to determine secondary structure content (α-helices, β-sheets).
- Molecular dynamics simulations to model protein-ligand interactions.
Main Results:
- Active G-protein conformations are more stable and compact than inactive ones.
- Activated wild-type subunits showed greater recovery of native structure and nucleotide-binding ability after heat-induced denaturation.
- Denaturation pathways differed between Giα1 and Gsα, with Giα1 denaturation initiating at tryptophan residues and Gsα at secondary structure disruption.
- A stabilizing π-cation interaction between arginine and tryptophan residues was identified in active conformations.
Conclusions:
- The active state of Gα subunits is conformationally more stable and compact, contributing to their signaling function.
- Specific residues and their interactions, such as π-cation interactions, play a significant role in G-protein subunit stability.
- These findings provide insights into the structural basis of G-protein function and potential therapeutic targets for G-protein-associated diseases.
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