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bioRxiv · 10.1101/2021.03.02.433577

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

Fowle, H.·Zhao, Z.·Xu, Q.·Wang, X.·Adeyemi, M.·Feiser, F.·Kurimchak, A.·Kettenbach, A. N.·Page, R.·Peti, W.·Dunbrack, R. L.·Grana, X.
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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/B55, specifically recognizes substrates and presents them to the enzyme active site. Here, we show how the PP2A regulatory subunit B55 recruits p107, a pRB-related tumor suppressor and B55 substrate. Using molecular and cellular approaches, we identified a conserved region 1 (R1, residues 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 B55 binding and dephosphorylation of the proximal pSer-615 in vitro and in cells. Numerous B55/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 dephosphorylation by PP2A/B55, validating its generality. A data-guided computational model details the interaction of residues from the conserved p107 SLiM, the B55 groove, and phosphosite presentation. Altogether these data provide key insights into PP2A/B55 mechanisms of substrate recruitment and active site engagement, and also facilitate identification and validation of new substrates, a key step towards understanding PP2A/B55[<] role in multiple cellular processes.

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Fowle, H., Zhao, Z., Xu, Q., Wang, X., Adeyemi, M., Feiser, F., Kurimchak, A., Kettenbach, A. N., Page, R., Peti, W., Dunbrack, R. L., Grana, X.. 2021-03-03. PP2A/B55α substrate recruitment as defined by the retinoblastoma-related protein p107. https://doi.org/10.1101/2021.03.02.433577

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