Neutron diffraction from oriented multibilayers has been used to study the bilayer interaction of the amphipathic peptide salmon calcitonin. Penetration of calcitonin into bilayers composed of dioleoylphosphatidylcholine increases with the addition of 15% (mol) of the anionic phospholipid dioleoylphosphatidylglycerol. Neutron scattering profiles of water distribution in stacked bilayers show a continuous band of deuterons across each bilayer, consistent with the suggestion that the hormone forms transbilayer α-helixes under these conditions. These experiments add to the growing body of data on the role of phosphatidylglycerol in bilayer insertion of protein helices and suggests a possible evolutionary history for calcitonin.
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