Phosphorylation and functions of inhibitor-2 family of proteins.
Protein phosphatase-1 (PP1) is an essential protein Ser/Thr phosphatase that is extraordinarily conserved from yeast to human, and Inhibitor-2 (I-2) is the most ancient of the heat-stable proteins specific for PP1. We identified novel I-2 homologues in Caenorhabditis elegans (Ce) and Xenopus laevis (Xe) and compared them to the I-2 proteins from Homo sapiens (Hs), Saccharomyces cerevisiae (GLC8), and Drosophila melanogaster (Dm). The Ce I-2 and Dm I-2 showed the highest potency inhibition of rabbit PP1 with IC50 near 5 nM compared to Hs I-2 and Xe I-2 with IC50 between 10 and 50 nM and GLC8 with >100-fold lower activity. Inhibition of PP1 bound to Nek2 kinase activated the kinase to phosphorylate a C-Nap1 domain substrate. All the species of I-2 except GLC8 activated the Nek2::PP1 to the same extent as microcystin-LR. Only Hs I-2 and Xe I-2, not the I-2 proteins more divergent in sequence, directly activated human Aurora-A kinase. Various species of I-2 have a common PxTP phosphorylation site that showed a wide range of reactivity with GSK3, ERK, or CDC2/cyclinB1 kinases. The Suc1 subunit of CDC2/cyclinB1 enhanced reactivity with I-2, consistent with this being a site of mitotic phosphorylation. The results show species specificity among the I-2 family within the context of conserved PP1 inhibitory activity and variable phosphorylation by Pro-directed kinases.
Li
Mingguang
M
Center for Cell Signaling and Department of Microbiology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA.
Satinover
David L
DL
Brautigan
David L
DL
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017931:DNA Primers; D004268:DNA-Binding Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D056488:Histone Chaperones; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
D002868:Chromosomal Proteins, Non-Histone; D017931:DNA Primers; D004268:DNA-Binding Proteins; D056488:Histone Chaperones; C513473:SET protein, human; D014157:Transcription Factors