Evolutionary crossroads of cell signaling: PP1 and PP2A substrate sites in intrinsically disordered regions

Abstract

Phosphorylation of the hydroxyl group of the amino acids serine and threonine is among the most prevalent post-translational modifications in mammalian cells. Phospho-serine (pSer) and -threonine (pThr) represent a central cornerstone in the cell's toolbox for adaptation to signal input. The true power for the fast modulation of the regulatory pSer/pThr sites arises from the timely attachment, binding and removal of the phosphate. The phosphorylation of serine and threonine by kinases and the binding of pSer/pThr by phosphorylation-dependent scaffold proteins is largely determined by the sequence motif surrounding the phosphorylation site (p-site). The removal of the phosphate is regulated by pSer/pThr-specific phosphatases with the two most prominent ones being PP1 and PP2A. For this family, recent advances brought forward a more complex mechanism for p-site selection. The interaction of regulatory proteins with the substrate protein constitutes a first layer for substrate recognition, but also interactions of the catalytic subunit with the amino acids in close proximity to pSer/pThr contribute to p-site selection. Here, we review the current pieces of evidence for this multi-layered, complex mechanism and hypothesize that, depending on the degree of higher structure surrounding the substrate site, recognition is more strongly influenced by regulatory subunits away from the active site for structured substrate regions, whereas the motif context is of strong relevance with p-sites in disordered regions. The latter makes these amino acid sequences crossroads for signaling and motif strength between kinases, pSer/pThr-binding proteins and phosphatases.

Structural mechanism for inhibition of PP2A-B56α and oncogenicity by CIP2A

“…6E ). Notably, among the enriched motifs, 14-3-3 protein binding motif is a firmly established PP2A-B56α target in many signal transduction proteins 49 . Further, recent studies indicate functional relationship between PP2A-B56 and CLK2 in different physiological and pathological context 50 , 51 .…”

“…Thereby, and especially as different B-subunit containing PP2A complexes can have even opposite cellular functions, such as tumour suppression or oncogenesis 54 , understanding the function and regulation of individual PP2A B-subunits is essential. Amino acid sequence determinants for selective recognition of target proteins have recently been discovered for some PPP regulatory subunits 1,10,14,42,49,55 . However, whether the regions of regulatory subunits mediating the substrate interactions.…”

Leishmania PNUTS discriminates between PP1 catalytic subunits through an RVxF–ΦΦ–F motif and polymorphisms in the PP1 C-tail and catalytic domain

“…Treatment of cell lysates with or without calf intestinal phosphatase and conditions we have demonstrated to dephosphorylate pol II ( 64 ) had no effect on Wdr82 gel mobility (data not shown), excluding the possibility that the observed shift in Wdr82 is due to changes in phosphorylation status. The AlphaFold-predicted Wdr82 structure indicates that the N terminus ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ) of Wdr82 has low prediction confidence, followed by potentially solvent-exposed 34 FYTGIN 39 sequence susceptible for cleavage by chymotrypsin and thermolysin ( Fig. S12 A ), suggesting a disordered N terminus region prone to proteolytic cleavage.…”

“…Phosphoprotein phosphatase 1 (PP1) is a major serine/threonine phosphatase, estimated to catalyze one-third of all dephosphorylation events in eukaryotic cells and involved in many essential cellular activities (including cardiac muscle contraction, glycogen metabolism, cell cycle transition, and transcription termination) ( 4 , 5 , 6 ). In contrast to protein serine/threonine kinases, although PP1 exhibits some intrinsic preference for pThr versus pSer and motifs surrounding the phosphorylation sites ( 7 , 8 , 9 ), the substrate specificity of PP1 is largely conferred by regulatory interactors of PP1 (RIPPOs) (previously referred to as PP1-interacting proteins) ( 2 , 10 , 11 , 12 , 13 ). Therefore, to carry out specific functions in a wide variety of cellular activities, PP1 binds over 200 confirmed RIPPOs, forming highly specific holoenzymes in mammalian cells ( 2 , 13 , 14 , 15 ).…”

Derivatives of the Fungal Natural Product Illudalic Acid Inhibit the Activity of Protein Histidine Phosphatase PHPT1

“…Protein phosphorylation is a common post-translational modification that occurs in a variety of cellular contexts and is mediated by the opposing actions of protein kinases and protein phosphatases. [1][2][3][4] In contrast to the wealth of information in the literature about serine, threonine, and tyrosine phosphorylation, [1,[5][6][7][8] relatively little is known about the importance of phosphorylation at other amino acids. [9,10] In particular, elucidating the biological roles of histidine phosphorylation in mammalian cells has been a topic of intense interest [11][12][13][14] and controversy [15] recently.…”