ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Protein phosphatase 1 catalytic subunit (PP1C) is highly enriched in isolated rat postsynaptic densities. Gel overlay analyses using digoxigenin (DIG)-labeled PP1C revealed four major rat brain PP1C-binding proteins (PP1bps) with molecular masses of ≈216, 175, 134, and 75 kDa, which were (1) more abundant in brain than other rat tissues; (2) differentially expressed in microdissected brain regions; and (3) enriched in isolated cortex postsynaptic densities. PP1bp175, PP1bp134, PP1bp75, and PP1C were partially released from forebrain particulate extracts by incubation at low ionic strength, which destabilizes the actin cytoskeleton. Size-exclusion chromatography of solubilized extracts separated two main PP1 activities (≈600 and ≈100 kDa). PP1bps and PP1Cγ1 were enriched in the ≈600-kDa peak, but PP1Cβ was enriched in the ≈100-kDa peak. Furthermore, PP1bp175 and PP1bp134 exhibited lower binding of recombinant DIG-PP1Cβ than recombinant DIG-PP1Cγ1 or DIG-PP1Cα. Solubilized PP1bp175 and PP1bp134 interact with PP1C under native conditions, because they both (1) coeluted from size-exclusion and ion-exchange columns; (2) bound to microcystin-LR-Sepharose; and (3) coprecipitated using PP1C antibodies. Trypsinolysis of the ≈600-kDa form of PP1 increased phosphorylase a phosphatase activity approximately fourfold, suggesting that interaction of PP1C with these PP1bps modulates its activity. Thus, brain PP1 activity is likely targeted to the cytoskeleton, including postsynaptic densities, by isoform-selective binding of PP1C to these targeting/regulatory subunits, contributing to the specificity of its physiological roles.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1471-4159.1997.69030920.x
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