Oa. Bizzozero et al., Chemical deacylation reduces the adhesive properties of proteolipid protein and leads to decompaction of the myelin sheath, J NEUROCHEM, 76(4), 2001, pp. 1129-1141
Myelin proteolipid protein (PLP) contains thioester-bound, long-chain fatty
acids which are known to influence the structure of the molecule. To gain
further insights into the role of this post-translational modification, we
studied the effect that chemical deacylation of PLP had on the morphology o
f myelin and on the protein's ability to mediate the clustering of lipid ve
sicles. Incubation of rat optic nerves in isoosmotic solutions containing 1
00 mm hydroxylamine (HA) pH 7.4 led to deacylation of PLP and decompaction
of myelin lamellae at the level of the intraperiod line. Incubation of nerv
es with milder nucleophilic agents (Tris and methylamine) or diluted HA, co
nditions that do not remove protein-bound fatty acids, caused no alteration
s in myelin structure. Other possible effects of HA which could have affect
ed myelin compaction indirectly were ruled out. Incubation of optic nerves
with 50 mm dithioerythritol (DTE) also led to the splitting of the myelin i
ntraperiod line and this change again coincided with the removal of fatty a
cids. In addition, the apparently compacted CNS myelin in the PLP-less myel
in-deficient rat, like that in tissue containing deacylated PLP, was readil
y decompacted upon incubation in isoosmotic buffers, suggesting that the fu
nction of PLP as a stabilizer of the interlamellar attachment is, at least
in part, mediated by fatty acylation. Furthermore, in contrast to the nativ
e protein, PLP deacylated with either HA or DTE failed to induce the cluste
ring of phosphatidylcholine/cholesterol vesicles in vitro. This phenomenon
is not due to side-effects of the deacylation procedure since, upon partial
repalmitoylation, the protein recovered most of its original vesicle-clust
ering activity. Collectively, these findings suggest that palmitoylation, b
y influencing the adhesive properties of PLP, is important for stabilizing
the multilamellar structure of myelin.