Brain Proteolipids

Abstract

Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Nat flux and electrical conductance measurements. Single channel events were observed at low protein concentrations, in particular with one of the final homogeneous apoproteolipids of molecular mass 24 kDa.

A specific immunological probe for the major myelin proteolipid

“…Total bovine brain proteolipids and pure bovine MMPL were obtained as described in [12]. Pure bovine DM-20 was purified as described in [12] or 1131.…”

“…Pure bovine DM-20 was purified as described in [12] or 1131. Myelin and total rat brain proteolipids were obtained from adult Wistar rats as reported [14, 151. Two rabbits were injected subcutaneously on days 0,20 and 48 with 300 ~1 of a solution containing 1 mg of synthetic peptide 117-129 coupled to KLH and 300 @I of either Freund's complete adjuvant (day 0) or incomplete adjuvant (days 20 and 48).…”

Purification of a presynaptic membrane protein that mediates a calcium-dependent translocation of acetylcholine.

“…After lipid removal and ether precipitation, mediatophore lost its activity but became water soluble as has been found to be the case for proteolipids (31)(32)(33)(34); this permitted us to determine the Stokes radius, the sedimentation coefficient, and to calculate a molecular mass of 210 ± 16 kDa. The method introduces large possible errors, because a difference of 0.75 S for sedimentation coefficient gives a difference of =20 kDa for molecular mass.…”

Proteolipid Protein: Is It More than Just a Structural Component of Myelin?

“…In one study, the conductance across an artifi cial lipid bilayer measured by transmembrane " Na* flux was increased by incorporation of a proteolipid purified from whole brain homogenate [117], Although this PLP was not positively identified, it had a molecular mass of 24 kD, an N-terminal glycine and a C-tenninal phenyl alanine, characteristics of myelin PLP. In other studies, dicyclohexylcarbodiimide, an inhibitor of proton translo cation, was shown to preferentially bind the myelin PLP and to inhibit proton translocation in liposomes contain ing myelin PLP [122,123], This finding was later con firmed and shown not to be due to contamination with the PLP subunit of the mitochondrial Fo-ATPase which has similar binding properties [89].…”

“…Among the most likely possibilities, and one for which some experimental evidence exists, is that myelin Dev Ncurosci 1996;18:297-308PLP may form part of an ion channel or pore complex within cell membranes and myelin. Other PLPs seem to be involved in channel formation in the sarcoplasmic reticulum Ca3'-ATPase, yeast membrane H*-ATPase, kidney Na'-KZ-ATPase and mitochondrial Fo-ATPase [41,117,118]. Additionally, the reputed structure of myelin PLP/DM-20 is homologous with a large group of proteins which also contain 4 membrane-spanning regions and which function as ion channels.…”