MONOCLONAL-ANTIBODY O-10 DEFINES A CONFORMATIONALLY SENSITIVE CELL-SURFACE EPITOPE OF PROTEOLIPID PROTEIN (PLP) - EVIDENCE THAT PLP MISFOLDING UNDERLIES DYSMYELINATION IN MUTANT MICE
M. Jung et al., MONOCLONAL-ANTIBODY O-10 DEFINES A CONFORMATIONALLY SENSITIVE CELL-SURFACE EPITOPE OF PROTEOLIPID PROTEIN (PLP) - EVIDENCE THAT PLP MISFOLDING UNDERLIES DYSMYELINATION IN MUTANT MICE, The Journal of neuroscience, 16(24), 1996, pp. 7920-7929
Mutations in the gene for proteolipid protein (PLP) have been associat
ed with CNS dysmyelination and abnormal oligodendrocyte death in spont
aneous mouse mutants and in Pelizaeus-Merzbacher disease; however, the
effect of mutations on PLP structure and function are little understo
od. We have identified a monoclonal antibody directed against a novel
cell surface epitope of PLP, termed O10. By immunofluorescence analysi
s, COS-7 cells transiently transfected to express PLP (or its isoform
DM20) can be stained with antibody O10 and another antibody (A431) dir
ected against the C terminus of PLP/DM20. The subcellular distribution
of immunofluorescence labels for the two antibodies is not identical,
suggesting that the O10 epitope is acquired post-translationally. Whe
n PLP/DM20 from jimpy, jimpy(msd), and rumpshaker mutant mice is expre
ssed in COS-7 cells and compared with wild-type PLP/DM20, none of the
mutant isoforms displays the O10 epitope, whereas the C-terminal epito
pe is detected. Because the O10 but not the A431 epitope is also sensi
tive to SDS and reducing agents, this strongly suggests abnormal prote
in folding in the PLP mutants. PLP from jimpy(msd) mice is obviously m
isfolded, because the amino acid substitution (Ala(242) --> Val) is lo
cated within a transmembrane domain to which the O10 antibody does not
bind. We propose that the O10 epitope emerges as the full length prot
ein reaches a functional tertiary structure and that the absence of th
is epitope marks a structural defect of PLP that leads to dysmyelinati
on.