Fig. 8: Relating the amino acid preference of PP1c and PP2Ac to holoenzymes.

a The acidic groove is much more pronounced in PP1c compared to PP2Ac. Structures for PP1 catalytic subunit alpha isoform (PDB ID 3EGG, chain A)⁵⁰ and PP2A catalytic subunit alpha isoform (PDB ID 4I5L, chain C)⁶⁹ were retrieved from www.pdb.org (accessed 25 Oct 2019) and inspected in PyMOL v2.3.3. * marks the catalytic cleft containing two Mn²⁺ ions. Color coding between −5 (red) to +5 (blue) K_bT/e_. b Aligned structures of PP1c and PP2Ac (see above for details) highlighting residues which determine differences in acidic properties (orange spheres). The sequence alignment to determine corresponding residues was carried out in Needle (EMBOSS). Color coding of structures: PP1c in blue/black, PP2Ac in red/gray. Residues constituting the acidic groove have previously been defined by Zhang et al.⁷⁰ c Interaction of PP2Ac with B56/B´/PR61 based on the crystal structure of the trimeric holoenzyme with the scaffolding subunit A (PR65) derived from PDB ID 2NPP⁴⁸. Negatively charged amino acids within the binding regions of B56 to PP2Ac are highlighted. d The holoenzyme of PP1 has an intrinsic preference for basic motifs due to the composition of the acidic groove of the catalytic core protein. PP2A holoenzymes are per se not primed towards amino acid sequence features of 14-3-3 or PKA motifs, but need to associate to regulatory subunits such as B56 carrying acidic patches to achieve basophilic sequence specificity. e Both, PP1 and PP2A holoenzymes have a preference for pT due to a higher catalytic efficiency of their respective catalytic subunits towards pT over pS.