BINDING OF THE NEURONAL PROTEIN-B-50, BUT NOT THE METABOLITE-B-60, TO CALMODULIN

Abstract: : Protein kinase C phosphorylates the neurone‐specific protein B‐50 at a single Ser41 residue, which is also the point for a major proteolytic cleavage in vitro, and probably in vivo, that produces a B‐50 phosphorylation‐inhibiting N‐terminal fragment and a large C‐terminal metabolite B‐60 (B‐5041‐226). The intact purified protein will bind to calmodulin in the absence of calcium, but the interaction has an absolute requirement for dephospho‐B‐50. In an attempt to unify two aspects of B‐50 biochemistry, we have examined the interaction of B‐50 binding to calmodulin and B‐50 proteolysis. HPLC‐ and affinity‐purified B‐50 bound to calmodulin, but purified B‐60 did not. To ensure that this effect was not due to the phosphorylation state of pure, isolated B‐60, the metabolite was generated in vitro using a Triton extract of synaptosomal plasma membranes, which contains the as yet uncharacterized B‐50 protease. B‐60 derived from dephospho‐B‐50 also failed to bind calmodulin. The results demonstrate a direct connection between B‐50 binding to calmodulin and B‐50 proteolysis. The position of the proposed calmodulin‐binding domain within intact B‐50 is discussed in light of the failure of calmodulin to bind B‐60. Copyright © 1990, Wiley Blackwell. All rights reserved