Abstract
Angiotensin II AT1A receptor is coupled to G-protein, and the molecular mechanism of signal transduction is still unclear. The solution conformation of a synthetic peptide corresponding to residues 300-320 of the rat AT1A receptor, located in the C-terminal cytoplasmic tail and indicated by mutagenesis work to be critical for the G-protein coupling, has been investigated by circular dichroism (CD), nuclear magnetic resonance (NMR) and restrained molecular dynamics calculations. The CD data indicate that, in acidic water, at concentration below 0.8 mM, the peptide exists in a predominantly coil structure while at higher concentration it can form helical aggregates; addition of small amounts of trifluoroethanol induces a secondary structure, mostly due to the presence of helical elements. Using NMR-derived constraints, an ensemble of conformers for the peptide has been determined by restrained molecular dynamics calculations. Analysis of the converged three-dimensional structures indicates that a significant population of them adopts an amphipathic alpha-helical conformation that, depending upon experimental conditions, presents a variable extension in the stretch Leu6-Tyr20. An equilibrium with nonhelical structured conformers is also observed. We suggest that the capability of the peptide to modulate its secondary structure as a function of the medium dielectric constant, as well as its ability to form helical aggregates by means of intermolecular hydrophobic interactions, can play a significant role for G-protein activation.
Highlights
Mutational studies on angiotensin II AT1A1 receptor have indicated that residues or sequences of the cytoplasmic tail and loops, close to the membrane, are critical for G-protein coupling [1,2,3,4]
Working hypothesis is yet very speculative, it is certainly accepted that contacts between the receptor cytoplasmic portions and G-protein must take place and, that the secondary structure of those sequences is of great importance
It has been shown that the synthetic peptide representing the fragment 306 –320 of the rat AT1A receptor is able to activate purified Gi1, Gi2, and G0 proteins [3]
Summary
Mutational studies on angiotensin II AT1A1 receptor have indicated that residues or sequences of the cytoplasmic tail and loops, close to the membrane, are critical for G-protein coupling [1,2,3,4]. As far as the receptor C-terminal (CT) portion, the 21-mer near the membrane surface, corresponding to the sequence 300 –320 in the rat AT1A receptor, has been predicted to have a high probability to assume an amphipathic helical structure. It has been shown that the synthetic peptide representing the fragment 306 –320 of the rat AT1A receptor is able to activate purified Gi1, Gi2, and G0 proteins [3]. These observations have prompted us to investigate the solution conformation of the synthetic fragment LFYGFLGKKFKKYFLQLLKYI-NH2, fCT300–320, to verify if it may assume a helical structure and if its secondary structure can be modulated by physical or chemical, physiologically relevant perturbations. The peptide was studied in water, as well as in acidic H2O, 2,2,2 trifluoroethanol (TFE) mixtures, at 28 and 5 °C
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
