INTERACTION OF BOVINE MYELIN BASIC-PROTEIN WITH CHOLESTEROL

The interaction of myelin basic protein with cholesterol and the confo rmational changes occurring in the protein upon interaction with the l ipid were investigated. The myelin basic protein (MBP) plays an import ant role in stabilizing the multilamellar structure of the myelin memb rane. MBP interacts in a specific way with the lipids components of th e membrane. The major lipid component is the cholesterol which compris es 40-44 mol% of the lipids. In order to understand the effect of the lipids in the protein conformation we have studied the interaction bet ween MBP and cholesterol. The conformational changes induced in the pr otein upon interaction with different concentrations of cholesterol we re characterized by transmission electron microscopy (TEM) and monolay er studies. Aqueous solution of MBP from bovine brain (obtained by the method of Cheifetz and Moscarello) exhibited a circular dichroism (CD ) spectrum characteristic of random coil protein molecules. Upon addit ion of cholesterol, MBP-cholesterol complexes were observed by TEM. Th e monolayer compression experiments show plateaus in their surface pre ssure-area isotherms. The presence of these plateaus has previously be en interpreted as ac-helix conformation. By seeding the MBP onto the a queous support, we have determined the compression work for the protei n on the surface. Experimental areas of the mixtures MBP-cholesterol a re smaller than the area calculated by adding the areas of the pure co mponents, indicating that there are attractive forces between both com ponents. The calculated entropy of compression indicates that the high est organization is reached when lipid and protein are almost in the s ame proportion, (C) 1998 Academic Press.