Folding of G α Subunits: Implications for Disease States.

Autor: Najor M; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States., Leverson BD; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States., Goossens JL; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States., Kothawala S; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States., Olsen KW; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States., Mota de Freitas D; Department of Chemistry and Biochemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States.
Jazyk: angličtina
Zdroj: ACS omega [ACS Omega] 2018 Oct 31; Vol. 3 (10), pp. 12320-12329. Date of Electronic Publication: 2018 Oct 01.
DOI: 10.1021/acsomega.8b01174
Abstrakt: 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 G iα1 or G sα 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 G iα1 and G sα . 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 G iα1 . We found that as the temperature increased, G α 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 G iα1 , 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 G sα , 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 G α subunits. The folding properties of G α subunits reported here are discussed in the context of diseases associated to G-proteins.
Competing Interests: The authors declare no competing financial interest.
Databáze: MEDLINE
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