Gl. Mendz et al., INTERACTIONS OF MYELIN BASIC-PROTEIN WITH PALMITOYLLYSOPHOSPHATIDYLCHOLINE - CHARACTERIZATION OF THE COMPLEXES AND CONFORMATIONS OF THE PROTEIN, European biophysics journal, 24(1), 1995, pp. 39-53
The stoichiometry of palmitoyllysophosphatidylcholine/myelin basic pro
tein (PLPC/MBP) complexes, the location of the protein in the lysolipi
d micelles, and the conformational changes occurring in the basic prot
ein and peptides derived from it upon interaction with lysolecithin mi
celles were investigated by circular dichroic spectropolarimetry, ultr
acentrifugation, electron para magnetic resonance (EPR) and P-31, C-13
, and H-1 nuclear magnetic resonance spectroscopy (NMR), and electron
microscopy. Ultracentrifugation measurements indicated that well-defin
ed complexes were formed by the association of one protein molecule wi
th approximately 141 ly solipid molecules. Small-angle X-ray scatterin
g data indicated that the PLPC/MBP complexes form particles with a rad
ius of gyration of 3.8 nm. EPR spectral parameters of the spin labels
5-, and 16-doxylstearate incorporated into lysolecithin/basic protein
aggregates, and C-13- and H-1-NMR relaxation times of PLPC indicated t
hat the addition of the protein did not affect the environment and loc
ation of the labels and the organization of the lysolipid micelles. Th
e data suggested that MBP lies primarily near the surface of the micel
les, with segments penetrating beyond the interfacial region into the
hydrophobic interior, but without any part of the protein being protec
ted against rapid exchange of its amide groups with the aqueous enviro
nment. The basic protein acquired about 20% alpha-helix when bound to
lysolipid micelles. Circular dichroic spectra of sequential peptides d
erived by cleavage of the protein revealed the formation of alpha-heli
cal regions in the association with lysolecithin. Specific residues in
myelin basic protein that participated in binding to the micelles wer
e identified from magnetic resonance data on changes in the chemical s
hifts and intensities of assigned resonances, and line broadening of p
eaks by fatty acid spin-labels incorporated into the micelles.