Evidence to support a spectrum of active states for the glucagon receptor
| Autor: | N.A. Evans, Frank E. Blaney, N. Strudwick, Nirmala Bhogal, John B. C. Findlay |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
Alanine
endocrine system medicine.medical_specialty education.field_of_study Binding Sites Chemistry Mutant Population Glucagon Biochemistry Molecular biology Partial agonist Binding Competitive Kinetics Endocrinology Internal medicine medicine Receptors Glucagon Animals Humans Receptor education Ternary complex Glucagon receptor |
| Zdroj: | Biochemical Society transactions. 32(Pt 6) |
| ISSN: | 0300-5127 |
| Popis: | The ternary complex model suggests that G-protein-coupled receptors resonate between inactive (R) and active (R*) forms. Physiologically, R sites ordinarily predominate with a few R* sites giving rise to basal activity. Agonists recognize, stabilize and increase the R* population, thus altering intracellular activity. There is evidence to suggest the possibility of a spectrum of conformations between R and R*. Our aim is to study the consequences of putative GR (glucagon receptor)-activating mutations using glucagon and partial agonist des-His 1 -[Glu 9 ]glucagon amide (glucagon-NH 2 ). Alanine substitution in TM (transmembrane) helix 2 of Arg 173 or of His 177 detrimentally affected glucagon and glucagon-NH 2 response maxima. TM2 receptor mutant, Phe 181 -Ala, displayed reduced maximum cAMP accumulation in response to glucagon-NH 2 . Thr 353 -Cys (TM6) and Glu 406 -Ala (TM7) receptors demonstrated constitutive activity and enhanced EC 50 values for glucagon-NH 2 ; Arg 346 -Ala (TM6) and Asn 404 -Ala (TM7) receptors were activated by sub-fmol glucagon concentrations, yet were not constitutively active and demonstrated wild-type receptor-like EC 50 values for glucagon-NH 2 . Unlike Arg 346 -Ala receptors, Thr 353 -Cys, Asn 404 -Ala and Glu 406 -Ala receptors demonstrated improved EC 50 values for glucagon, whereas their maximal responses to and their affinity for glucagon were comparable with the wild-type receptor. In contrast, despite slightly reduced glucagon-NH 2 affinity, Arg 346 -Ala, Thr 353 -Cys, Asn 404 -Ala and Glu 406 -Ala receptors displayed glucagon-NH 2 response maxima that exceeded those seen for wild-type receptors. Interestingly, we observed biphasic glucagon-mediated signalling responses. Our results are consistent with the concept of different agonists promoting the formation of distinct active states from partially active R* low to fully active R* high forms. |
| Databáze: | OpenAIRE |
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