Effects of acyl chain length on the conformation of myelin basic protein bound to lysolipid micelles

The interactions of myelin basic protein with micelles of lysophosphatidylcholine detergents of different acyl chain lengths were investigated by circular dichroism (CD), small-angle X-ray scattering, Fourier transform infrared spectroscopy (FT-IR), and 1H, 13C and 31P nuclear magnetic resonance spectroscopy (NMR). Circular dichroic, FT-IR, and 1H NMR measurements indicated that the conformational changes induced in the protein molecules by association with micelles depended on the acyl chain length of the detergents. Size is one of the physical properties of micelles which is a function of the length of the acyl chains. The radii of gyration of detergent micelles in complexes with the protein measured by small-angle X-ray scattering indicated that the average size of the micelles was a quadratic function of the acyl chain length. The dependence of the protein conformational changes on micelle size was used to ascertain the order in which different protein segments associate with the detergents. Several procedures were employed to change the fluidity of micelles formed with detergents of given acyl chain lengths. The conformational changes observed on the MBP molecule by varying the micelle properties without changing the length of the chain, suggested that the changes depended on the size and fluidity of the micelles.