Thomas, Rosalee Cara; (1994) Conformational analysis of a receptor cytoplasmic domain. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A putative cytoplasmic domain of a membrane receptor was synthesised and studied in solution by electronic circular dichroism (CD), fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (1H nmr) as part of an attempt to elucidate the three dimensional structure of a membrane receptor by summing the structures of environmentally determined domains. Circular dichroism was used to screen the range of conformations adopted by the peptide in various media prior to nmr studies of preferred conformational states. Water and 90% methanol/water were selected as convenient media to study the two predominant states identified by CD. Perturbation CD and FTIR studies and simulation of experimental CD spectra using the conformers identified by deconvolution of FTIR Amide I bands were consistent with a molecule adopting three conformations, alpha helix, beta turn and extended helix (LHE), the position of the equilibrium being dependent on temperature, solvent, pH and ionic strength but with alpha helix favoured relative to LHE in organic solvents and LHE the preferred conformer in aqueous systems. In organic solvents concentration dependent beta sheet formation was observed. In 90% methanol/water the nmr data were consistent with a locus of stable helical structure between residues (8) and (16) and population of more extended conformers relative to helical conformers toward the peptide termini. In water the data were consistent with an equilibrium between beta turn, extended helix and extended structure. The absence of long range contacts in both media was consistent with a linear molecule. All or none of the conformations identified could be important in receptor signal transduction.

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