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Limited proteolysis of myelin basic protein in a system mimetic of the myelin interlamellar aqueous space
1Biomédicale des Saints-Pères, Laboratoire des Systèmes Moléculaires Organisés, Paris, France.
Abstract:
We have investigated the early steps of myelin basic protein (MBP) degradation in a membrane mimetic system (reverse micelles), resembling the interlamellar aqueous spaces where the protein is located in the myelin sheath. MBP, unfolded in buffer, refolds on incorporation into the micelles, resulting in reduced accessibility to three proteolytic enzymes, trypsin, cathepsin D, and Staphylococcus aureus V8 protease, in comparison with aqueous solution. Eleven cleavage sites seen in buffer are removed from proteolytic attack in micellar solution. These sites delineate a protected protein domain displaying a potential beta-sheet structure capable of interacting with the myelin membrane. An additional site not seen in buffer is attacked in the micelles. Experiments with a structure inducer, 15% 1-propanol in buffer, reveal that the refolding pattern of MBP in reverse micelles is specific to the membrane biomimetic system and is not produced by organic solvent per se. Micellar digestions of MBP generate long peptides, two of which, isolated after tryptic digestion, have been found to be immunodominant in multiple sclerosis patients. The findings suggest the structure induced in MBP by the micelles resembles that leading to production of the self-peptides recognized by T cells during proteolytic breakdown of MBP in autoimmune demyelinating diseases.
Insights
Myelin basic protein (MBP) refolds in a membrane-like environment, altering its protein degradation sites. This structural change in MBP may mimic autoimmune responses in demyelinating diseases.
Area of Science:
- Biochemistry
- Neuroscience
- Structural Biology
Background:
- Myelin basic protein (MBP) is a key component of the myelin sheath.
- Understanding MBP degradation is crucial for studying autoimmune demyelinating diseases.
Purpose of the Study:
- To investigate the early degradation of MBP in a membrane-mimetic system.
- To understand how MBP structure changes in a myelin sheath-like environment.
Main Methods:
- Utilized reverse micelles as a membrane mimetic system.
- Assessed proteolytic enzyme accessibility to MBP in micellar solution versus aqueous solution.
- Analyzed refolding patterns using a structure inducer (1-propanol).
Main Results:
- MBP refolds in reverse micelles, reducing accessibility to proteolytic enzymes.
- Eleven cleavage sites in aqueous solution were protected in micellar solution.
- A specific beta-sheet structure in MBP was identified within the micelles.
- Long peptides generated from micellar digestion were found to be immunodominant in multiple sclerosis patients.
Conclusions:
- The refolding of MBP in reverse micelles is specific to the membrane biomimetic system.
- The induced structure in MBP resembles self-peptides involved in autoimmune demyelination.
- Findings suggest a link between MBP structure, proteolytic breakdown, and T-cell recognition in autoimmune demyelinating diseases.