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Publication Abstract from PubMed

Inositol pyrophosphates (PP-InsPs) are 'energetic' intracellular signals that are ubiquitous in animals, plant and fungi; structural and biochemical characterization of PP-InsP metabolic enzymes provides insight into their evolution, reaction mechanisms, and regulation. Here, we describe the 2.35 A resolution structure of the catalytic core of Siw14, a 5-PP-InsP phosphatase from Saccharomyces cerevisiae, and a member of the protein tyrosinephosphatase (PTP) superfamily. Conclusions that we derive from structural data are supported by extensive site-directed mutagenesis and kinetic analyses, thereby attributing new functional significance to several key residues. We demonstrate the high activity and exquisite specificity of Siw14 for the 5-diphosphate group of PP-InsPs. The three structural elements that demarcate a 9.2 A deep substrate-binding pocket each have spatial equivalents in PTPs, but we identify how these are specialized for Siw14 to bind and hydrolyze the intensely negatively-charged PP-InsPs: (a), the catalytic P-loop with the Cx5RT/S PTP-motif contains additional, positively charged residues; (b), a loop between the alpha5 and alpha6 helices, corresponding to the Q-loop in PTPs, contains a lysine and an arginine that e xtend into the catalytic pocket due to displacement of the alpha5 helix orientation through intramolecular crowding caused by three bulky, hydrophobic residues; (c), the general acid loop in PTPs is replaced in Siw14 with a flexible loop that does not use an aspartate or glutamate as a general-acid. We propose that an acidic residue is not required for phosphoanhydride hydrolysis.

Structural and biochemical characterization of Siw14: a protein-tyrosine phosphatase fold that metabolizes inositol pyrophosphates.,Wang H, Gu C, Rolfes RJ, Jessen HJ, Shears SB J Biol Chem. 2018 Mar 14. pii: RA117.001670. doi: 10.1074/jbc.RA117.001670. PMID:29540476^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.