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1.
Biochem Biophys Res Commun ; 435(4): 567-73, 2013 Jun 14.
Article in English | MEDLINE | ID: mdl-23685145

ABSTRACT

TIMAP is an endothelial-cell predominant member of the MYPT family of PP1c regulatory subunits. This study explored the TIMAP-PP1c interaction and substrate specificity in vitro. TIMAP associated with all three PP1c isoforms, but endogenous endothelial cell TIMAP preferentially co-immunoprecipitated with PP1cß. Structural modeling of the TIMAP/PP1c complex predicts that the PP1c C-terminus is buried in the TIMAP ankyrin cluster, and that the PP1c active site remains accessible. Consistent with this model, C-terminal PP1c phosphorylation by cdk2-cyclinA was masked by TIMAP, and PP1c bound TIMAP when the active site was occupied by the inhibitor microcystin. TIMAP inhibited PP1c activity toward phosphorylase a in a concentration-dependent manner, with half-maximal inhibition in the 0.4-1.2 nM range, an effect modulated by the length, and by Ser333/Ser337 phosphomimic mutations of the TIMAP C-terminus. TIMAP-bound PP1cß effectively dephosphorylated MLC2 and TIMAP itself. By contrast, TIMAP inhibited the PP1cß activity toward the putative substrate LAMR1, and instead masked LAMR1 PKA- and PKC-phosphorylation sites. This is direct evidence that MLC2 is a TIMAP/PP1c substrate. The data also indicate that TIMAP can modify protein phosphorylation independent of its function as a PP1c regulatory subunit, namely by masking phosphorylation sites of binding partners like PP1c and LAMR1.


Subject(s)
Endothelial Cells/metabolism , Membrane Proteins/chemistry , Membrane Proteins/metabolism , Models, Molecular , Protein Phosphatase 1/metabolism , Animals , Cattle , Cells, Cultured , Receptors, Laminin/metabolism , Ribosomal Proteins
2.
Biochem J ; 449(3): 649-59, 2013 Feb 01.
Article in English | MEDLINE | ID: mdl-23088536

ABSTRACT

The serine/threonine PP-1c (protein phosphatase-1 catalytic subunit) is regulated by association with multiple regulatory subunits. Human ASPPs (apoptosis-stimulating proteins of p53) comprise three family members: ASPP1, ASPP2 and iASPP (inhibitory ASPP), which is uniquely overexpressed in many cancers. While ASPP2 and iASPP are known to bind PP-1c, we now identify novel and distinct molecular interactions that allow all three ASPPs to bind differentially to PP-1c isoforms and p53. iASPP lacks a PP-1c-binding RVXF motif; however, we show it interacts with PP-1c via a RARL sequence with a Kd value of 26 nM. Molecular modelling and mutagenesis of PP-1c-ASPP protein complexes identified two additional modes of interaction. First, two positively charged residues, Lys260 and Arg261 on PP-1c, interact with all ASPP family members. Secondly, the C-terminus of the PP-1c α, ß and γ isoforms contain a type-2 SH3 (Src homology 3) poly-proline motif (PxxPxR), which binds directly to the SH3 domains of ASPP1, ASPP2 and iASPP. In PP-1cγ this comprises residues 309-314 (PVTPPR). When the Px(T)PxR motif is deleted or mutated via insertion of a phosphorylation site mimic (T311D), PP-1c fails to bind to all three ASPP proteins. Overall, we provide the first direct evidence for PP-1c binding via its C-terminus to an SH3 protein domain.


Subject(s)
Adaptor Proteins, Signal Transducing/chemistry , Adaptor Proteins, Signal Transducing/metabolism , Apoptosis Regulatory Proteins/chemistry , Apoptosis Regulatory Proteins/metabolism , Protein Phosphatase 1/chemistry , Protein Phosphatase 1/metabolism , Adaptor Proteins, Signal Transducing/genetics , Amino Acid Sequence , Animals , Apoptosis Regulatory Proteins/genetics , Humans , Models, Molecular , Molecular Sequence Data , Multiprotein Complexes/chemistry , Multiprotein Complexes/genetics , Multiprotein Complexes/metabolism , Mutagenesis, Site-Directed , Neoplasms/genetics , Neoplasms/metabolism , Protein Interaction Domains and Motifs , Protein Phosphatase 1/genetics , Rabbits , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Homology, Amino Acid , Surface Plasmon Resonance , Tumor Suppressor Protein p53/chemistry , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/metabolism , src Homology Domains
3.
J Biol Chem ; 279(41): 43198-206, 2004 Oct 08.
Article in English | MEDLINE | ID: mdl-15280359

ABSTRACT

Protein phosphatase-1 and protein phosphatase-2B (calcineurin) are eukaryotic serine/threonine phosphatases that share 40% sequence identity in their catalytic subunits. Despite the similarities in sequence, these phosphatases are widely divergent when it comes to inhibition by natural product toxins, such as microcystin-LR and okadaic acid. The most prominent region of non-conserved sequence between these phosphatases corresponds to the beta12-beta13 loop of protein phosphatase-1, and the L7 loop of toxin-resistant calcineurin. In the present study, mutagenesis of residues 273-277 of the beta12-beta13 loop of the protein phosphatase-1 catalytic subunit (PP-1c) to the corresponding residues in calcineurin (312-316), resulted in a chimeric mutant that showed a decrease in sensitivity to microcystin-LR, okadaic acid, and the endogenous PP-1c inhibitor protein inhibitor-2. A crystal structure of the chimeric mutant in complex with okadaic acid was determined to 2.0-A resolution. The beta12-beta13 loop region of the mutant superimposes closely with that of wild-type PP-1c bound to okadaic acid. Systematic mutation of each residue in the beta12-beta13 loop of PP-1c showed that a single amino acid change (C273L) was the most influential in mediating sensitivity of PP-1c to toxins. Taken together, these data indicate that it is an individual amino acid residue substitution and not a change in the overall beta12-beta13 loop conformation of protein phosphatase-1 that contributes to disrupting important interactions with inhibitors such as microcystin-LR and okadaic acid.


Subject(s)
Calcineurin/chemistry , Phosphoprotein Phosphatases/chemistry , Phosphoprotein Phosphatases/genetics , Amino Acid Sequence , Crystallography, X-Ray , Dose-Response Relationship, Drug , Escherichia coli/metabolism , Humans , Kinetics , Marine Toxins , Microcystins , Models, Chemical , Models, Molecular , Molecular Sequence Data , Mutagenesis , Mutagenesis, Site-Directed , Mutation , Okadaic Acid/pharmacology , Peptides, Cyclic/pharmacology , Phosphoric Monoester Hydrolases/chemistry , Point Mutation , Protein Binding , Protein Conformation , Protein Phosphatase 1 , Protein Structure, Secondary , Protein Structure, Tertiary , Recombinant Proteins/chemistry , Substrate Specificity
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