Conformational differences of ovine and human corticotrophin releasing hormone A CD, IR, NMR and dynamic light scattering study

Publisher Website
Google Scholar
Abstract
The differences in the conformational properties of ovine (o) and human (h) CRH in aqueous solution, structure‐inducing TFE and in the presence of detergent micelles and lipid vesicles have been investigated by circular dichroism, Fourier transform infrared spectroscopy, NMR and dynamic light scattering. o‐CRH was found to exist as a monomer with little regular structure in dilute aqueous solution. Association at concentrations higher than 10−3 mol/L results predominantly in dimers. The induction of a substantial amount of intermolecular β‐structure seems to be the result of interactions of the C‐terminal hexapeptide and the N‐terminal region 6‐12 of o‐CRH chains in antiparallel orientation. In contrast, h‐CRH exhibits a high tendency of association which is highly sensitive to the pH. The formation of tetramers at millimolar peptide concentration is related to a helical content of ca. 50%. The potentially helical, highly hydrophobic region 6‐20 enlarged by more hydrophobic residues in position 23 and 25 is proposed to stabilize the h‐CRH associates. In the presence of structure inducing TFE (C‐terminal heptapeptide, as concluded on the basis of NMR studies. Both peptides bind to detergent micelles at pH 4 as well as 7.4 associated with an increase in the α‐helical content. Interaction of the two peptides with DMPC vesicles was found exclusively at pH 4. Above the phase transition temperature of DMPC the α‐helical content in h‐CRH increases slightly; however, o‐CRH reveals a substantial amount of β‐type structure. The intramolecular type of β‐structure is associated with a deeper insertion of the o‐CRH region 6‐12 into the hydrophobic region of the lipid bilayer, whereas the corresponding region of h‐CRH is kept in the bilayer surface. The higher helicity of h‐CRH might explain to some extent its higher affinity to the CRH receptor, CRH antibodies and the CRH binding protein. © Munksgaard 1996.