AbstractsProtein Phosphatase Mg 2+ /Mn 2+ -Dependent 1K (PPM1K), also named as PP2Cm or branched-chain a-ketoacid dehydrogenase complex phosphatase, is a member of the metal-dependent phosphatase family and an important metabolic regulator. Single nucleotide polymorphisms (SNPs) in PPM1K contributing to protein functional defects have been found to be associated with numerous human diseases, such as cardiovascular disease, maple syrup urine disease, type 2 diabetes, and neurological disease. PPM1K N94K is an identified missense mutant produced by one of the SNPs in the human PPM1K coding sequence. However, the effects of the N94K mutant on its activity and structural property have not been defined. Here, we performed a detailed enzymological study using steady-state kinetics in the presence of pNPP or phospho-peptide substrates and crystallographic analyses of the wild-type and N94K PPM1K. The PPM1K-N94K significantly impaired its Mg 2+ -dependent catalytic activity and structural analysis demonstrated that the N94K mutation induced a conformational change in the key residue in coordinating the Mg 2+ in the active site. Specifically, three Mg 2+ were located in the active site of 1 These authors contributed equally to this work. Abbreviations used: ALS, amyotrophic lateral sclerosis; BCAA, branched-chain amino acid; BCKA, branched-chain a-ketoacid; BCKD, branched-chain a-ketoacid dehydrogenase; BCKDE1a, branched-chain a-ketoacid decarboxylase (E1) alpha subunit; BDP, branched-chain a-ketoacid dehydrogenase phosphatase; BSA, bovine serum albumin; E. coli, Escherichia coli; E1b, branched-chain a-ketoacid decarboxylase/ dehydrogenase; EDTA, Ethylene-diaminetetraacetic acid; HEPES, 4-(2hydroxyethyl)-1-piperazine-ethanesulfonic acid; IPTG, isopropyl b-D-1thiogalactopyranoside; LB, Luria-Bertani broth; MSUD, maple syrup urine disease; PCR, polymerase chain reaction; p-E1b, phospho-E1b; PEG, polyethylene glycol; PMSF, phenylmethane sulfonyl fluoride; pNPP, p-nitrophenyl phosphate; PP2Cm, PP2C phosphatase of mitochondrial matrix residence; PPM1A, protein phosphatase Mg 2+ /Mn 2+ -Dependent 1A; PPM1G, protein phosphatase Mg 2+ /Mn 2+ -Dependent 1G; PPM1K, protein phosphatase Mg 2+ /Mn 2+ -Dependent 1K; PPM, metal-dependent protein phosphatase; RRID, research resource identifier; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TEV, tobacco etch virus; TRIS, tris(hydroxymethyl) aminomethane; WT, wild type.
550the PPM1K N94K instead of two Mg 2+ in the PPM1K wild type. Therefore, our results provide a structure basis for the metal ion-dependent PPM1K-N94K phosphatase activity.Keywords: active site, crystal structure, phosphatase activity, protein phosphatase Mg 2+ /Mn 2+ -dependent 1K, single nucleotide polymorphisms, third metal ion.