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Marburg's variant of multiple sclerosis correlates with a less compact structure of myelin basic protein
D R Beniac1, D D Wood, N Palaniyar
1Department of Molecular Biology and Genetics, University of Guelph, Ontario, Canada.
Abstract:
Multiple sclerosis (MS) is an autoimmune disease in which the myelin sheath of the central nervous system is degraded, and the 18.5 kDa isoform of myelin basic protein (MBP) is reduced in cationicity. In a unique case of acute, fulminating MS (Marburg's variant), MBP is considerably less cationic than MBP from both normal, and chronic MS-afflicted individuals. This electron microscopical study has identified that, in vitro, the less cationic Marburg MBP isomer forms a more extended protein-lipid complex than MBP from healthy or chronic MS-afflicted individuals. This correlation implies that chemical modifications to MBP in vivo contribute directly to the structural instability of myelin, and subsequent autoantigenic presentation of this protein, observed in vivo in MS.
Insights
Multiple sclerosis involves myelin sheath degradation. A unique Marburg variant shows less cationic myelin basic protein (MBP), forming extended complexes, suggesting chemical changes drive myelin instability in MS.
Area of Science:
- Neuroimmunology
- Structural Biology
- Biochemistry
Background:
- Multiple sclerosis (MS) is a central nervous system autoimmune disease targeting the myelin sheath.
- Myelin basic protein (MBP), a key myelin component, exhibits reduced cationicity in MS patients.
- The Marburg variant of MS presents with significantly less cationic MBP compared to normal or chronic MS individuals.
Purpose of the Study:
- To investigate the structural properties of less cationic myelin basic protein (MBP) found in a unique case of acute, fulminating multiple sclerosis (Marburg's variant).
- To explore the in vitro relationship between MBP cationicity, protein-lipid complex formation, and myelin structural integrity.
- To correlate in vitro findings with in vivo implications for myelin instability and autoantigenic presentation in MS.
Main Methods:
- Electron microscopy was employed to visualize and analyze protein-lipid complexes formed by different MBP isomers.
- Comparative analysis of MBP cationicity was performed between normal individuals, chronic MS patients, and the Marburg variant case.
- In vitro studies focused on the structural characteristics of complexes formed by MBP from these distinct groups.
Main Results:
- The less cationic MBP isomer from the Marburg MS variant formed a more extended protein-lipid complex in vitro compared to MBP from healthy individuals or those with chronic MS.
- This structural difference was observed using electron microscopy.
- A direct correlation was identified between reduced MBP cationicity and altered complex formation.
Conclusions:
- Chemical modifications to myelin basic protein (MBP) in vivo are strongly implicated in altering its structure and cationicity.
- These modifications contribute to the structural instability of the myelin sheath observed in multiple sclerosis.
- The altered MBP structure may facilitate subsequent autoantigenic presentation, driving the autoimmune response in MS.