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The effect of myelin basic protein on the endogenous phosphorylation of platelets
Abstract:
Bovine myelin basic protein (BP) induced a shape change and endogenous phosphorylation of a 45,000 (45K) molecular weight protein of intact human platelets. This effect occurred rapidly over an effective concentration range of 5-100 microM BP. BP peptides encompassing residues 1-42, 43-88, and 89-169 from the BP molecule of 169 residues, neither induced phosphorylation of platelets nor blocked the effect of intact BP. Subfractionation of disrupted platelets demonstrated the phosphorylated 45K protein in the 100,000 xg supernate. When isolated platelet membranes were used, no BP induced phosphorylation of a 45K protein could be detected. The amino acid composition of the purified, phosphorylated 45K protein differed from those of other known platelet proteins. BP itself was also phosphorylated by an endogenous platelet protein kinase(s) present both in the 100,000 xg supernatant and in the isolated membrane fraction of platelets. These results indicate that the normal or pathological release of BP from myelin may lead to phosphorylation of an internal protein of platelets and possibly other tissue elements with resultant metabolic and functional changes.
Insights
Bovine myelin basic protein (BP) triggers rapid shape changes and internal protein phosphorylation in human platelets. This suggests BP release may impact platelet function and metabolism.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Myelin basic protein (BP) is a key component of the myelin sheath.
- The role of BP in platelet activation and intracellular signaling is not fully understood.
Purpose of the Study:
- To investigate the effect of bovine myelin basic protein (BP) on human platelets.
- To identify the molecular mechanisms underlying BP-induced platelet responses.
Main Methods:
- Intact human platelets were treated with varying concentrations of BP.
- Platelet shape changes and endogenous protein phosphorylation were analyzed.
- Subcellular fractions of platelets were examined using ultracentrifugation.
- Amino acid composition of phosphorylated proteins was determined.
Main Results:
- Bovine BP induced rapid platelet shape change and phosphorylation of a 45,000 molecular weight (45K) protein within a concentration range of 5-100 microM.
- Specific BP peptides did not induce phosphorylation or block intact BP's effect.
- The phosphorylated 45K protein was located in the platelet supernatant, not membranes.
- BP itself was also phosphorylated by endogenous platelet kinases.
Conclusions:
- Bovine myelin basic protein induces phosphorylation of an internal platelet protein, suggesting a potential mechanism for BP's impact on platelet function.
- The release of BP from myelin, under normal or pathological conditions, may alter platelet metabolism and function.
- Further research is needed to explore the broader implications for other tissue elements.