Synthesis and spectroscopy of membrane receptor proteins.

The high-affinity receptor for lgE is a tetrameric complex of subunits of the type αβγ2. We report here conformational studies of the intact γ, subunit in trifluoroethanol and water/liposomes by circular dichroism and Fourier-transform infrared (FTIR) spectroscopy. In trifiuoroethanol, the FTIR amide I' frequencies were consistent with two predominant conformational components, the β-turn and αhelix, whilst in liposomes consisting of D2O and dimyristoylglycerophosphocholine (Myr2GroPCho), three components were observed. The third component present may contain some left-handed extended helix. Spectral simulation was carried out to demonstrate that the CD spectra were consistent with the component conformations identitied from FTIR spectroscopy. The simulated CD spectra were in excellent agreement with the experimental spectra. The intact y subunit conformation in trifluoroethanol was shown to possess 72% α-helical and 28% β-turn conformations. In water/ Myr2GroPCho liposomes the percentage of each conformational component present is 37%, 38% and 25% for the α-helix, β-turn and extended structures, respectively. Assuming that the transmembrane fragment was α-helical, an excellent correlation was found between this derived α-helical content in water/liposomes (37%) and from hydrophobicity plots where the percentage of amino acids in the transmembrane domain is predicted by others to be 34%. It is suggested that the β-turn detected by CD and FTIR was attributable to a 310 helix rather than a type I or type III reverse turn. [ABSTRACT FROM AUTHOR]

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