Dephosphorylation of neurofilament proteins enhances their susceptibility to degradation by calpain.
The degradation of phosphorylated and dephosphorylated neurofilament proteins by the Ca2+-activated neutral proteinase calpain was studied. Neurofilaments were isolated from bovine spinal cord, dephosphorylated by alkaline phosphatase (from Escherichia coli) and radioiodinated with [125I]-Bolton-Hunter reagent. The radioiodinated neurofilament proteins (untreated and dephosphorylated) were incubated in the presence and absence of calpain from rabbit skeletal muscle, and the degradation rates of large (NF-H), mid-sized (NF-M) and small (NF-L) neurofilament polypeptides were analysed by SDS/polyacrylamide-gel electrophoresis and autoradiography. The degradation of dephosphorylated neurofilament proteins occurred at a higher rate, and to a greater extent, than did that of the phosphorylated (untreated) neurofilament proteins. The dephosphorylated high-molecular-mass neurofilament (NF-HD) was proteolyzed 6 times more quickly than the untreated NF-H. The degradation rate of the NF-M and NF-L neurofilament proteins was also enhanced after dephosphorylation, but less than that of NF-H. This indicates that the dephosphorylation of neurofilament proteins can increase their sensitivity to calpain degradation.
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Laboratory of Neurochemistry, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, MD 20892.
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002154:Calpain / Q000378:metabolism*; D002417:Cattle; D007381:Intermediate Filament Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011817:Rabbits; D013997:Time Factors
D007381:Intermediate Filament Proteins; D000469:Alkaline Phosphatase; D002154:Calpain