Identification and biochemical characterization of the PP1‐binding protein: Consortin

Abstract

Protein phosphatase 1 (PP1), one of the major serine/threonine protein phosphatases in eukaryotic cells, controls various key biological pathways, including protein synthesis, carbohydrate metabolism, muscle contraction, cell cycle and neuron transmission, et al. The catalytic subunit of PP1 is in vivo associated with different regulatory subunits to form a variety of holoenzymes. These regulatory subunits target the enzyme to specific subcellular compartments and regulate the functions of its substrates. We have conducted the search for the new PP1‐binding proteins of heart cells by yeast two‐hybrid screen, and identified several candidate proteins. One of them is consortin, a connexin trafficking protein. Consortin was found to associate with PP1α in the co‐immunoprecipitation, and GST pull‐down assay. Mutation at the PP1‐binding motif of consortin disrupted binding with PP1. Immunofluorescence microscopic analysis revealed that the PP1/consortin complex was conspicuously localized at ER and Golgi. The recombinant consortin protein can inhibit PP1 with the IC50 of 3±0.2 nM, but fail to inhibit PP2A. Taken together, our results suggested that consortin is a PP1 binding protein and is capable of modulating PP1 activity.