title: Interaction of a G protein-coupled receptor with a G protein-derived peptide induces structural changes in both peptide and receptor: a Fourier-transform infrared study using isotopically labeled peptides.
abstract: G protein-coupled receptor signaling involves productive interaction between agonist-activated receptor and G protein. We have used Fourier-transform infrared difference spectroscopy to examine the interaction between the active Meta II state of the visual pigment rhodopsin with a peptide analogue corresponding to the C terminus of the alpha-subunit of the G protein transducin. Formation of the receptor-peptide complex evokes a spectral signature consisting of conformationally sensitive amide I and amide II difference bands. In order to distinguish between amide backbone contributions of the peptide and of the receptor moiety to the vibrational spectra, we employed complete (13)C,(15)N-labeling of the peptide. This isotopic labeling downshifts selectively the bands of the peptide, which can thus be extracted. Our results show that formation of the complex between the activated Meta II receptor state and the peptide is accompanied by structural changes of the peptide, and of the receptor, indicating that the conformation of the Meta II.peptide complex is different from that of Meta II. This result implies that the activated receptor state has conformational flexibility. Binding of the peptide to the activated receptor state stabilizes a substate that deviates from that stabilized only by the agonist.
authors.affiliation: Arbeitsgruppe Biophysik, Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany. reiner.vogel@hiophysik.uni-freiburg.de
authors.forename: Reiner
authors.initials: R
authors.lastname: Vogel
authors.forename: Swetlana
authors.initials: S
authors.lastname: Martell
authors.forename: Mohana
authors.initials: M
authors.lastname: Mahalingam
authors.forename: Martin
authors.initials: M
authors.lastname: Engelhard
authors.forename: Friedrich
authors.initials: F
authors.lastname: Siebert
mesh_terms: D000595:Amino Acid Sequence; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D007553:Isotope Labeling; D008956:Models, Chemical; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D015293:Transducin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; D012243:Rhodopsin; D005982:Glutathione Transferase; D019204:GTP-Binding Proteins; D015293:Transducin