Binding of the neuronal protein B-50, but not the metabolite B-60, to calmodulin.
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-50(41-226]. 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.
Coggins
P J
PJ
Department of Medical Physiology, University of Calgary, Alberta, Canada.
Zwiers
H
H
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002846:Chromatography, Affinity; D019922:GAP-43 Protein; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats
D002147:Calmodulin; D019922:GAP-43 Protein; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins