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A novel metalloproteinase associated with brain myelin membranes. Isolation and characterization
A Chantry1, N A Gregson, P Glynn
1Department of Neurochemistry, Institute of Neurology, London, United Kingdom.
Abstract:
Brain myelin membrane preparations contain a metalloproteinase activity which degrades myelin basic protein (MBP). The activity was associated with lentil lectin-binding glycoproteins solubilized from myelin and could be detected in the presence of the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate (CHAPS). The metalloproteinase represented about 5% of this glycoprotein fraction and was isolated from it by chromatography on DEAE-Sephacel, CM-Sepharose, and Superose 6. The proteinase had an apparent relative molecular weight (Mr) of approximately 58,000 both by gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Mr value was unaffected by the presence of reducing agents but was diminished to about 52,000 by treating the proteinase with endoglycosidase F. The purified proteinase cleaved many bonds in MBP but did not generate trichloroacetic acid-soluble products. Two major polypeptides, putatively MBP1-73 and MBP74-170, were prominent in digests of MBP by either the purified enzyme or myelin membranes. The proteinase was active between pH 7 and 9 and was inhibited by phenanthroline and dithiothreitol but not phosphoramidon or inhibitors of serine or cysteine proteinases. Histones, but not azocasein, also served as substrates for the proteinase. From its enzymic and molecular characteristics the myelin-derived metalloproteinase appears distinct from previously described enzymes.
Insights
Researchers identified a novel metalloproteinase in brain myelin that degrades myelin basic protein (MBP). This enzyme, distinct from others, cleaves MBP into specific fragments, offering new insights into myelin structure and degradation.
Area of Science:
- Neuroscience
- Biochemistry
- Enzymology
Background:
- Brain myelin contains metalloproteinase activity capable of degrading myelin basic protein (MBP).
- This activity is linked to specific glycoproteins within the myelin membrane.
Purpose of the Study:
- To isolate and characterize the metalloproteinase responsible for myelin basic protein degradation.
- To determine the enzyme's biochemical properties and substrate specificity.
Main Methods:
- Solubilization of glycoproteins from myelin using CHAPS detergent.
- Purification of the metalloproteinase via ion-exchange and size-exclusion chromatography.
- Determination of molecular weight, substrate cleavage patterns, and inhibitor profiles.
Main Results:
- A metalloproteinase of approximately 58,000 Mr was purified, showing reduced size after endoglycosidase F treatment.
- The enzyme cleaved MBP into specific fragments (MBP1-73 and MBP74-170) without producing soluble products.
- Optimal activity was observed between pH 7-9, with inhibition by phenanthroline and dithiothreitol; histones were substrates, but azocasein was not.
Conclusions:
- A novel myelin-derived metalloproteinase distinct from previously described enzymes was identified.
- The enzyme's specific cleavage of MBP suggests a role in myelin structure maintenance or turnover.
- Further characterization could elucidate its function in neurological processes.