PP2A/B55α substrate recruitment as defined by the retinoblastoma-related protein p107

Abstract

Protein phosphorylation is a reversible post-translation modification essential in cell signaling. This study addresses a long-standing question as to how the most abundant serine/threonine Protein-Phosphatase 2 (PP2A) holoenzyme, PP2A/B55α, specifically recognizes substrates and presents them to the enzyme active site. Here, we show how the PP2A regulatory subunit B55α recruits p107, a pRB-related tumor suppressor and B55α substrate. Using molecular and cellular approaches, we identified a conserved region 1(615-626) encompassing the strongest p107 binding site. This enabled us to identify an "HxRVxxV619-625" short linear motif (SLiM) in p107 as necessary for B55α binding and dephosphorylation of pSer-615 in vitro and in cells. Numerous B55α/PP2A substrates, including TAU, contain a related SLiM C-terminal from a proximal phosphosite, "p[ST]-P-x(5-10)-[RK]-V-x-x-[VI]-R". Mutation of conserved SLiM residues in TAU dramatically inhibits PP2A/B55α-mediated dephosphorylation, validating its generality. A data-guided computational model details the residue interactions from the conserved p107 SLiM, the B55α groove, and phosphosite presentation.

VPA mediates bidirectional regulation of cell cycle progression through the PPP2R2A-Chk1 signaling axis in response to HU

“…6D-I). In addition, PPP2R2A D197 was previously reported to be a key site for Tau and P107 recruitment [42,43], suggesting PPP2R2A D197 might serve as a conserved pivotal amino acid in mediating PPP2R2A substrate recognition. This acidic top may use substrate specific sequences to distinguish its different binding partners, and the PPP2R2A D197 or/and PPP2R2A N181 may be key recognition sites for multiple substrates.…”

“…PP2A is a critical Ser/Thr protein phosphatase that relies on its B-regulatory subunits to specifically recruit substrates [42,44,45]. Previous reports have highlighted that PPP2R2A may perform different functions due to the potential presence of different substrate recruitment sites [46][47][48].…”

“…To further investigate which sites in PPP2R2A would be essential for the regulation of Chk1 dephosphorylation and contribute to VPA-bidirectional effects, we used 9 Myc-tagged PPP2R2A variants (Fig. 6A) which lie in the top of the β-propeller [42,43]. By coimmunoprecipitation, we found PPP2R2A D197K and N181A variants showed the most profound impact on the binding of Chk1 when directly compared to wild-type (WT) PPP2R2A (Fig.…”

PP2A‐B55 and its adapter proteins IER2 and IER5 regulate the activity of RB family proteins and the expression of cell cycle‐related genes

“…Phosphorylated p107 is a known substrate for PP2A/B55a [17][18][19], and IER5 enhances p107 dephosphorylation by PP2A. The B55a subunit binds to the 'spacer region' between pockets A and B of p107 [51], whereas IER5 binds to the N-and C-terminal regions. The multiple interactions of IER5-PP2A/B55 and p107 enhance PP2A activity towards p107.…”

Human SLFN5 and its Xenopus Laevis ortholog regulate entry into mitosis and oocyte meiotic resumption

“…For the B55 regulatory subunit it was shown that basic residues flanking a minimal CDK consensus sequence promoted B55 dephosphorylation [ 15 , 19 ]. However, a 20 amino acid polybasic region containing three arginine residues was identified as crucial for PP2A-B55 binding to mCRTC3 and recently a short linear motif (HxRVxxV) could be identified as mediator of B55α binding in p107, a member of the Retinoblastoma tumor suppressor protein family [ 20 , 21 ]. SLFN5 contains only a single small basic motif (RKRK) at its C-terminus and some additional pairs of basic amino acids which are distributed along the protein.…”