Phosphorylation Modulates Calpain‐Mediated Proteolysis and Calmodulin Binding of the 200‐kDa and 160‐kDa Neurofilament Proteins

Abstract: The effects of enzymatic dephosphorylation on neurofilament interaction with two calcium‐binding proteins, calpain and calmodulin, were examined. Dephosphorylation increased the rate and extent of 200‐kDa neurofilament protein proteolysis by calpain. In contrast, dephosphorylation of the 160‐kDa neurofilament protein did not alter the rate or extent of calpain proteolysis. However, the calpain‐induced breakdown products of native and dephosphorylated 160‐kDa neurofilament protein were different. Dephosphorylation did not change the proteolytic rate, extent, or breakdown products of the 68‐kDa neurofilament protein. Calmodulin binding to the purified individual 160‐ and 200‐kDa neurofilament proteins was increased following dephosphorylation. These results suggest that phosphorylation may regulate the metabolism and function of neurofilaments by modulating interactions with the calcium‐activated proteins calpain and calmodulin.