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ADP-ribosyltransferase activity in myelin membranes isolated from human brain
C Boulias1, F G Mastronardi, M A Moscarello
1Division of Biochemistry Research, Hospital for Sick Children, Toronto, Ontario, Canada.
Abstract:
An ADP-ribosyltransferase has been identified in compact myelin and in several white matter fractions which contain less compact myelin, fractionated on the basis of increasing protein/lipid ratios. One fraction the P3A contained the greatest activity although the activity in compact myelin was only slightly less. The ADP-ribosyltransferase activity of solubilized myelin was stimulated by increasing amounts of GTP gamma S and was specific for the beta-isomer of NAD. Although ADP-ribosylation was demonstrated with the heterotrimeric G proteins in the 40-50 kDa range, the substrate for the ADP-ribosyltransferase in the 20 kDa range was identified as MBP. ADP-ribosyltransferase; myelin basic protein; signal transduction.
Insights
Researchers found an ADP-ribosyltransferase enzyme in myelin, crucial for brain signal transduction. This enzyme targets myelin basic protein (MBP), suggesting a role in myelin function and repair.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Myelin, the protective sheath around nerve fibers, plays a critical role in efficient signal transmission in the central nervous system.
- Dysfunction in myelin is implicated in various neurological disorders, highlighting the need to understand its molecular components and regulatory mechanisms.
Purpose of the Study:
- To identify and characterize an ADP-ribosyltransferase enzyme within myelin.
- To determine the substrates and regulatory factors of this myelin-associated ADP-ribosyltransferase.
Main Methods:
- Fractionation of white matter to isolate myelin and subfractions based on protein/lipid ratios.
- Assay of ADP-ribosyltransferase activity using GTPγS and specific NAD isomers.
- Identification of protein substrates using SDS-PAGE and molecular weight analysis.
Main Results:
- An ADP-ribosyltransferase was detected in compact myelin and various white matter fractions, with highest activity in the P3A fraction.
- Enzyme activity was stimulated by GTPγS and showed specificity for the beta-isomer of NAD.
- The enzyme ADP-ribosylated heterotrimeric G proteins (40-50 kDa) and, significantly, myelin basic protein (MBP) in the 20 kDa range.
Conclusions:
- A novel ADP-ribosyltransferase is present in myelin, with a strong association with myelin basic protein.
- This finding suggests a potential role for ADP-ribosylation in myelin structure, function, or signal transduction pathways within the white matter.