Binding of myelin basic protein to phospholipid micelles

Resonances of 1H NMR spectra (360 MHz) due to several individual substituents of myelin basic protein reconstituted into phospholipid micelles have been resolved and assigned. With the aid of spin echo techniques to remove overlapping signals in the region of 2-3 ppm, singlet resonances due to the two myelin basic protein methionine S--CH3 groups (Met-20 and Met-167) and the Ala-1 N-acetyl methyl group were observed. In the presence of sufficient lysophosphatidylcholine to fully bind the protein, differential broadening occurred for Met S--CH3 resonances; Met-20 lost about 40% of its original integrated intensity (while displaying no significant line broadening) but Met-167 and N-acetyl-Ala-1 resonances did not appear to be influenced by lipid. The differential broadening of the Met-20 (versus the Met-167 and N-acetyl-Ala-1) resonances was proposed to arise from (a) specific restriction to local molecular motion of the Met-20 (but not Met-167) side chain (i.e. due to its penetration into the hydrophobic micelle lipid matrix or its proximity to specific protein/lipid electrostatic sites); or (b) transmitted dynamic effects of overall protein binding to micellar particles (due to the relatively fewer degrees of rotational freedom available to Met-20 versus N-acetyl-Ala-1 and Met-167 near protein termini). Evidence favoring the latter alternative is presented.