Comprehensive snapshots of an unusual reaction cycle for an atypical protein tyrosine phosphatases (PTP)

Inositol pyrophosphates (PP‐InsPs) are “energetic” intracellular signals that are ubiquitous in animals, plants, and fungi. We are characterizing new proteins that regulate PP‐InsP metabolism and/or function as their ‘receptors'. Here, we describe our structural characterization of At1g05000, an Arabidopsis member of the cysteine‐based protein tyrosine phosphatase family that exhibits higher reactivity towards PP‐InsPs than phosphoproteins. We provide 20 high resolution crystal structures which describe how this atypical PTP has been repurposed to become the most active of known PP‐IPs phosphatases. These structures include complexes with different ligands including inositol pyrophosphates, polyphosphates and nucleotides; together they reveal pre‐reactant, reactant, intermediate and product states. As a consequence, we describe an atypical mechanism: an exceptionally electropositive ‘P’‐loop that immobilizes the β‐phosphate for hydrolysis; the opposite end of the substrate is anchored by Lys and Arg residues in a loop that is pushed into the binding pocket due to intramolecular crowding; a canonical catalytic acid is sacrificed to avoid electrostatic clashing with the substrate; a conserved water is identified to function as the proton donor; two catalytic important residues, His156 and Arg188, form π‐cation interactions that are important for positioning substrate and the catalytic water; hydrolyzed phosphate ion is rotated during catalysis. Overall, our data support a substrate‐driven reaction mechanism. Furthermore, this work opens up new directions for studying regulatory interactions of PP‐InsPs with human protein tyrosine phosphatases. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .