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ADP-ribosylation of myelin basic protein and inhibition of phospholipid vesicle aggregation
C Yamamori1, M Terashima, H Ishino
1Department of Psychiatry, Shimane Medical University, Izumo, Japan.
Abstract:
Four isoforms of myelin basic protein (MBP) from chicken brain were ADP-ribosylated by chicken heterophil ADP-ribosyltransferase. The 21-kD isoform was the most preferential substrate of this transferase. With this isoform, the Km values were estimated to be 330 mumol/l for NAD and 30 mumol/l for MBP, and the optimal pH for ADP-ribosylation was 8.5. The stoichiometry of ADP-ribose incorporation into 21-kD MBP was 3.5 mol of ADP-ribose/mol MBP. We found the inhibition of ADP-ribosylation of MBP by hydroxylamine and L-arginine indicating that this modification was likely to be mediated by arginine residues. Proteolytic peptide maps of ADP-ribosylated MBP by chicken ADP-ribosyltransferase and cholera toxin showed partially different radio active bands. When 21-kD MBP was ADP-ribosylated by chicken transferase, the potential for phospholipid vesicle aggregation was reduced in proportion of the degree of ADP-ribosylation. The possibility that ADP-ribosylation of MBP may control stabilization of myelin through regulation of its affinity for phospholipid in vivo would need to be considered.
Insights
Chicken heterophil ADP-ribosyltransferase modifies myelin basic protein (MBP). This ADP-ribosylation of MBP reduces its ability to aggregate phospholipids, potentially impacting myelin stabilization.
Area of Science:
- Biochemistry
- Neuroscience
- Molecular Biology
Background:
- Myelin basic protein (MBP) is crucial for myelin sheath formation and stability in the central nervous system.
- ADP-ribosylation is a post-translational modification that can alter protein function.
Purpose of the Study:
- To investigate the ADP-ribosylation of chicken brain myelin basic protein (MBP) by chicken heterophil ADP-ribosyltransferase.
- To determine the characteristics of this enzymatic modification and its effect on MBP function.
Main Methods:
- ADP-ribosylation assays using purified MBP isoforms and chicken heterophil ADP-ribosyltransferase.
- Kinetic analysis (Km values) and pH optimum determination.
- Inhibition studies using hydroxylamine and L-arginine.
- Proteolytic peptide mapping.
- Phospholipid vesicle aggregation assays.
Main Results:
- The 21-kD MBP isoform was identified as the preferred substrate.
- Optimal ADP-ribosylation occurred at pH 8.5 with Km values of 330 µmol/l for NAD and 30 µmol/l for MBP.
- Modification involves arginine residues and reduces MBP's ability to induce phospholipid vesicle aggregation.
- ADP-ribosylation by chicken transferase and cholera toxin yielded distinct peptide maps.
Conclusions:
- ADP-ribosylation by chicken heterophil ADP-ribosyltransferase modifies MBP, particularly the 21-kD isoform.
- This modification, likely targeting arginine residues, impairs MBP's interaction with phospholipids.
- The findings suggest a potential regulatory role for MBP ADP-ribosylation in myelin stabilization in vivo.