title: Identification of a novel PSR as the substrate of an SR protein kinase in the true slime mold.
abstract: Here, a novel cDNA encoding a serine/arginine (SR)-rich protein, designated PSR, was isolated from the true slime mold Physarum polycephalum and expressed in Escherichia coli. The deduced amino acid (aa) sequence reveals that PSR contains RS repeats at its C-terminus, similar to the conventional PSRPK substrate ASF/SF2. To study the novel protein, we generated a variety of mutant constructs by PCR and site-directed mutagenesis. Our analysis indicated that the purified recombinant PSR was phosphorylated by PSRPK in vitro and the SR-rich domain (amino acids 460-469) in the PSR protein was required for phosphorylation. In addition, removal of the docking motif (amino acids 424-450) from PSR significantly reduced the overall catalytic efficiency of the phosphorylation reaction. We also found that the conserved ATP-binding region (62)LGWGHFSTVWLAIDEKNGGREVALK(86) and the serine/threonine protein kinases active-site signature (184)IIHTDLKPENVLL(196) of PSRPK played a crucial role in substrate phosphorylation and Lys(86) and Asp(188) were crucial for PSRPK phosphorylation of PSR. These results suggest that PSR is a novel SR-related protein that is phosphorylated by PSRPK.
authors.affiliation: Institute of Genetics and Cytology, Northeast Normal University, Changchun, P.R. China.
authors.forename: Yong-Xia
authors.initials: YX
authors.lastname: Zhang
authors.forename: Miao
authors.initials: M
authors.lastname: Xing
authors.forename: Xuan
authors.initials: X
authors.lastname: Fei
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Zhang
authors.forename: Sheng-Li
authors.initials: SL
authors.lastname: Tian
authors.forename: Ming-Hua
authors.initials: MH
authors.lastname: Li
authors.forename: Shi-De
authors.initials: SD
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D008969:Molecular Sequence Data; D009235:Myxomycetes / Q000201:enzymology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D011494:Protein Kinases