Structure of the Proteolipid Protein Extracted from Bovine Central Nervous System Myelin with Nondenaturing Detergents

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Abstract
As a basis for attempts to define the structures of the proteins within myelin, methods have been developed for their extraction and isolation in solutions of non-denaturing detergents. With use of solutions of deoxycholate or Triton X-100, up to 90% of the protein has been extracted from bovine CNS myelin, along with most of the phospholipid. The proteolipid protein has been purified in deoxycholate solutions by chromatography on a blue dye-ligand column, which retained all of the basic protein and 2′,3′-cyclic nucleotide-3′-phosphodiesterase, and then on Sephacryl S300, which separated proteolipid protein from phospholipid and high-molecular-weight proteins. The proteolipid protein was isolated from Triton X-100 extracts of myelin by adsorption onto phosphocellulose resin, with subsequent elution by 0.5 M sodium chloride. Gel permeation chromatography was used as the final purification step. Sedimentation equilibrium experiments gave a monomer molecular weight of 134,000 ± 8000 in deoxycholate and 145,000 ± 17,000 in Triton X-100 solutions. On the basis of an apparent subunit molecular weight of 23,500 it was deduced that the native protein is probably hexameric. Above 0.2 gL−1 in Triton X-100 solutions and 0.5 gL−1 in deoxycholate solutions the protein aggregated. In deoxycholate solutions the protein adopts the highly helical conformation expected for an intrinsic membrane protein.

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