Physical properties of bovine white matter proteolipid apoprotein–sodium dodecyl sulfate complexes

Abstract

The interaction of bovine white matter proteolipid apoproteins with sodium dodecyl sulfate (SDS) was studied. Equilibrium dialysis binding measurements show that the apoprotein binds approximately 1.5 gm SDS per gram protein at high ionic strength (gamma/2 = 0.17). At low ionic strength (gamma/2 = 0.01) the protein binds only 0.90 gm per gram protein. The Stokes radius of the proteolipid protein is 40 A. Based on the circular dichroism spectrum, the apoprotein contains less than 20% alpha -helix structure in either aqueous or 0.1% sodium dodecyl sulfate solution. Analytical SDS-PAGE (polyacrylamide gel electrophoresis) revealed two polypeptides. The major proteolipid protein migrated with an apparent molecular weight of 26,000 daltons. The minor proteolipid protein exhibited a molecular weight of 22,200 daltons. The apoprotein showed a marked tendency to aggregate on 8 M urea-SDS-polyacrylamide gels or when heated at 100 degree in excess detergent. These results suggest that the proteolipid proteins have hydrophobic regions that are not embedded within the detergent micelle but are exposed to the solvent. These regions may serve as sites for intermolecular aggregation.

Identification of a New Exon in the Myelin Proteolipid Protein Gene Encoding Novel Protein Isoforms That Are Restricted to the Somata of Oligodendrocytes and Neurons

“…2) with the expected mobility predicted by the open reading frame. The higher molecular weight bands observed in the analysis of the total products are probably aggregates of PLP, DM20, and srDM20, a phenomenon observed by many investigators (Chan and Lees, 1974;Sakura, 1981;Bizzozero et al, 1982;Trifilieff et al, 1986).…”

“…In PLP and DM20 Western blots of brain, the detection of higher and lower molecular weight products was somewhat variable. The higher molecular weight bands are generally believed to be aggregates of PLP and/or DM20 (Chan and Lees, 1974;Sakura, 1981;Bizzozero et al, 1982;Trifilieff et al, 1986), and the lower molecular weight bands have not yet been identified, although partial peptide sequences have been obtained for the bovine proteins (Lepage et al, 1986). Our results would suggest that some of these bands contain the peptide encoded by exon 1.1.…”