High performance liquid chromatography of integral glycoproteins of peripheral nerve myelin

Towards crystallization of hydrophobic myelin glycoproteins: P0 and PASII/PMP22

The preparation of a pure and homogeneous protein sample at proper concentration is a prerequisite for success when attempting their crystallization for structural determination. The detergents suitable for solubilization particularly of membrane proteins are not always the best for crystallization. Myelin of the peripheral nervous system of vertebrates is the example of a membrane for which neutral or "gentle" detergents are not even strong enough to solubilize its proteins. In contrast, sodium- or lithium-dodecyl sulfate is very effective. We solubilized myelin membrane in 2%(w/v) sodium dodecyl sulfate, followed by chromatographic purification of the hydrophobic myelin glycoproteins P0 and PASII/PMP22, and finally, we have exchanged the sodium dodecyl sulfate bound to protein for other neutral detergents using ceramic hydroxyapatite column. Theoretically, we should easily exchange sodium dodecyl sulfate for any neutral detergent, but for some of them, the solubility of myelin glycoproteins is low. To monitor the potential variability in the secondary structure of glycoproteins, we have used circular dichroism. Sodium dodecyl sulfate seems to be the appropriate detergent for the purpose of purification of very hydrophobic glycoproteins, since it can be easily exchanged for another neutral detergent.

Separation of the major proteins of central and peripheral nervous system myelin using reversed-phase high-performance liquid chromatography

A general method to separate the major proteins of rat central and peripheral nervous system myelin has been developed. The key step is the initial quantitative removal of the lipids under conditions where the proteins retain their solubility in HPLC solvents. Lipids are removed by a combination of solvent extraction and column chromatography on Sephadex LH-60 in 2-chloroethanol:10 mM HCl (9:1). Proteins are then separated by reversed-phase (RP) HPLC. Samples are applied to a wide pore reversed-phase C-3 column and eluted with a linear gradient of 10-70% 1-propanol in 0.1% trifluoroacetic acid (0-100% B) over a 60-min period. Myelin basic proteins elute between 25 and 30% B, Wolfgram and other high molecular weight proteins at 35-50% B, proteolipid protein at 65-80% B, and P0 glycoprotein at 55-65% B. This elution pattern is consistent with the known relative hydrophobicity of these proteins. Protein recovery for the entire procedure is greater than 74%. Proteolipid and P0 proteins isolated by HPLC contain 2.3 and 1.1 mol of covalently bound fatty acids, respectively. This fatty acid composition is similar to that previously reported using different isolation procedures. The analysis of central and peripheral nervous system myelin proteins by RP-HPLC permits the isolation of purified proteins for structural and metabolic experiments.