Membrane topology of the myelin/oligodendrocyte glycoprotein

Abstract

Myelin/oligodendrocyte glycoprotein (MOG), a specific component of the mammalian central nervous system, is located on the surface of the oligodendrocyte plasma membrane and the outermost lamellae of mature myelin; it is expressed during the latter steps of myelinogenesis. It has been shown that MOG may play a pathological role in autoimmune demyelinating diseases of the central nervous system, although its physiological function remains unknown. MOG is an integral membrane glycoprotein with an extracellular immunoglobulin-like domain and two hydrophobic segments which were predicted to be membranespanning on the basis of hydropathy analysis. As a first step in elucidation of MOG function, we have investigated its membrane topology, combining immunofluorescence studies on cultured oligodendrocytes and MOG-transfected Chinese hamster ovary cells with biochemical analyses, including in vitro translation, membrane insertion and protease-digestion assays. Our results indicate that the C-terminal tail of MOG is located into the cytoplasm, and that only the first hydrophobic region of MOG spans the membrane whereas the second hydrophobic region appears to be semi-embedded in the lipid bilayer, lying partially buried in the membrane with its N-terminal and C-terminal boundaries facing the cytoplasm.Keywords : MOG; myelin; topology.Central nervous system myelin is synthesized as an extension of the oligodendrocyte plasma membrane, which wraps around axons in a concentric multilamellar sheath. Proteolipid proteins (PLP) and myelin basic proteins (MBP) are the most abundant components [1], accounting for about 80% of the protein. Myelin also contains minor glycoprotein components, such as myelin-associated glycoprotein (MAG) and myelin/oligodendrocyte glycoprotein (MOG).MOG was originally identified as the antigen recognized by the demyelinating antibodies present in serum of animals immunized with whole-brain homogenate [2] and was later characterized as a 26 kDa to 28-kDa glycoprotein [3]. Given its late expression during myelinogenesis in mammals [4Ϫ6] and its location at the membrane surface of oligodendrocytes and external lamellae of myelin sheaths [4,7], MOG has been proposed to play a role either in the completion and maintenance of myelin sheath [5,8], or in the adhesion of adjacent myelinated tracts [9]. However, in vivo and in vitro studies suggested that MOG may be a target autoantigen in autoimmune demyelinating diseases of the central nervous system. In animals with experimental autoimmune encephalomyelitis, an experimental model for multiple sclerosis, the injection of MOG peptides can initiate [12,13] and tolerization assays in a non-human primate model of experimental autoimmune encephalomyelitis led to a lethal encephalopathy [14]. The physiopathological mechanism responsible for this particular and deleterious effect of MOG humoral immunoreactivity may result from the fixation of a component of complement, C1q, to the extracellular domain of MOG [15].Sequence comparison of MOG cDNAs from rat, bovine, ...

Myelin/oligodendrocyte glycoprotein–deficient (MOG-deficient) mice reveal lack of immune tolerance to MOG in wild-type mice

“…Indeed, the size of the responding unfractionated or CD4 + T cell population, as assessed by IFN-γ ELISPOT, was indistinguishable between MOG +/+ and MOG -/-mice. Moreover, our analysis revealed new immunogenic peptides localized in both hydrophobic regions of MOG (20). Strikingly, both MOG +/+ and MOG -/-mice mount a similar T cell in vitro response to these peptides, indicating that the lack of tolerance to the Ig-like domain extends also to the transmembrane and cytoplasmic domains of MOG.…”

“…Total protein extracts (100 µg) of mouse brain were run on an SDS polyacrylamide gel, then electroblotted onto a nitrocellulose membrane (Amersham Biosciences Corp.). The membrane was incubated with anti-MOG antibodies directed against the carboxy-terminal or the Ig-like extracellular domain of MOG (1:1,000 dilution) (20), then with secondary peroxidase-conjugated goat anti-rabbit IgG (Sigma-Aldrich, St. Louis, Missouri, USA) and then processed according to ECL protocol (Amersham Biosciences Corp.).…”

Antibodies to native myelin oligodendrocyte glycoprotein are serologic markers of early inflammation in multiple sclerosis

“…CHO cells were transfected with a full-length construct corresponding to the major ␣-1 form of human MOG as described (28). CHO cells were cultured in T-225 flasks (Costar), in RPMI medium 1640 supplemented with 10% FCS, 1ϫ Glutamax, 1 mM sodium pyruvate, and 50 g͞ml gentamycine.…”

Commentary: Sorting the wheat from the chaff: identifying demyelinating components of the myelin oligodendrocyte glycoprotein (MOG)‐specific autoantibody repertoire

“…MOG is a quantitatively minor type I membrane glycoprotein that is preferentially incorporated into the outermost surface of the myelin sheath [37] where a single extracellular immunoglobulin-like domain -MOG immunoglobulin domain (MOG Igd ) -is exposed to the extracellular milieu [38][39][40]. It is this domain of the molecule that is recognized by demyelinating MOG-specific antibodies.…”