Biomedical subjects

J Kuret

Publications and source records attributed to J Kuret.

At least 37 records · Page 2Linked to original sources

PubMed1996

Prenylated isoforms of yeast casein kinase I, including the novel Yck3p, suppress the gcs1 blockage of cell proliferation from stationary phase.

The GCS1 gene of the budding yeast Saccharomyces cerevisiae mediate the resumption of cell proliferation from the starved, stationary-phase state. Here we identify yeast genes that, in increased dosages, overcome the growth defect of gcs1 delta mutant cells. Among these are YCK1 (CK12) and YCK2 (CKI1), encoding membrane-associated casein kinase I, and YCK3, encoding a novel casein kinase I isoform. Some Yck3p gene product was found associated with the plasma membrane, like Yck1p and Yck2p, but most confractionated with the nucleus, like another yeast casein kinase I isoform, Hrr25p. Genetic studies showed that YCK3 and HRR25 constitute an essential gene family and that Yck3p can weakly substitute for Yck1p-Yck2p. For gcs1 delta suppression, both a protein kinase domain and a C-terminal prenylation motif were shown to be necessary. An impairment in endocytosis was found for gcs1 delta mutant cells, which was alleviated by an increased YCK2 gene dosage. The ability of an increased casein kinase I gene dosage to suppress the effects caused by the absence of Gcs1p suggests that Gcs1p and Yck1p-Yck2p affect parallel pathways.

Amino Acid Sequence↗

PubMed1995

Crystal structure of casein kinase-1, a phosphate-directed protein kinase.

The structure of a truncated variant of casein kinase-1 from Schizosaccharomyces pombe, has been determined in complex with MgATP at 2.0 A resolution. The model resembles the 'closed', ATP-bound conformations of the cyclin-dependent kinase 2 and the cAMP-dependent protein kinase, with clear differences in the structure of surface loops that impart unique features to casein kinase-1. The structure is of unphosphorylated, active conformation of casein kinase-1 and the peptide-binding site is fully accessible to substrate.

Adenosine Triphosphate↗

PubMed1994

Molecular cloning and sequence analysis of two novel fission yeast casein kinase-1 isoforms.

The cDNAs for two casein kinase-1 homologs, hhp1 and hhp2, have been isolated from Schizosaccharomyces pombe and characterized. Their corresponding genes reside on chromosomes II and I, respectively, and encode approximately 42-46 kDa proteins that are related structurally to the HRR25 gene product of budding yeast. On the basis of multiple sequence alignment, the CK1 family appears to consist of three main branches. We predict that the branch containing the hhp genes encodes nuclear kinases involved in the regulation of DNA metabolism.

Amino Acid Sequence↗

PubMed1994

A prenylation motif is required for plasma membrane localization and biochemical function of casein kinase I in budding yeast.

The subcellular distribution of three casein kinase I (CK1) homologs, encoded by the YCK1, YCK2, and HRR25 genes, has been determined in budding yeast through a combination of subcellular fractionation and immunofluorescence methods. Both Yck proteins are tightly associated with the plasma membrane or underlying cytoskeleton and require both high-salt and nonionic detergent for extraction. Association is mediated primarily by the prenylation motif found at the C terminus of both Yck proteins. In contrast, the third CK1 homolog, Hrr25p, is found predominantly in the nucleus and only partially in the plasma membrane. Despite partial colocalization with the Yck proteins, Hrr25p is unable to rescue the yck1 delta yck2 delta phenotype. However, a chimeric kinase containing the N-terminal kinase domain of Hrr25p and the C-terminal region of Yck2p contains full Yck activity in vivo. These data suggest that members of the casein kinase I family have distinct but partially overlapping distributions in the cell that are mediated by their unique C-terminal regions.

Base Sequence↗

PubMed1994

Cytoplasmic forms of fission yeast casein kinase-1 associate primarily with the particulate fraction of the cell.

Two novel casein kinase-1 homologs, cki1+ and cki2+, have been isolated from Schizosaccharomyces pombe and characterized. Both genes reside on chromosome II and encode approximately 50-kDa proteins that are related structurally and enzymatically to the YCK gene products of budding yeast. Subcellular fractionation experiments demonstrate that Cki1 and Cki2 are both cytoplasmic enzymes that do not overlap in subcellular distribution and that probably play distinct roles within the cell. Although gene disruption experiments show that neither cki1+ nor cki2+ is essential for cell viability, overexpression of cki2 leads to a severe growth defect and aberrant morphology. Cells become round or pear shaped and separate poorly following septation. These results suggest that of the four members of the casein kinase-1 family recognized in fission yeast, one member, Cki2, may contribute to the regulation of cell morphology.

Amino Acid Sequence↗

PubMed1994

Expression, purification, crystallization, and preliminary x-ray analysis of casein kinase-1 from Schizosaccharomyces pombe.

The catalytic domain of Schizosaccharomyces pombe casein kinase-1 (the product of the cki1 gene) has been overexpressed in Escherichia coli, purified by chromatographic methods, characterized in vitro, and crystallized in the presence and absence of nucleotide substrate. The best crystals belong to the trigonal space group P3(1)21 or its enantiomorph, have unit cell parameters a = b = 79 A, c = 121 A, and diffract x-rays to 2.0-A resolution. Kinetic characterization of the purified catalytic domain and other C-terminal deletion mutants of Cki1 suggests that it is subject to two forms of regulation. One mechanism involves autophosphorylation, and results in a 4-fold decrease in the affinity for protein substrate. In contrast, truncation of intact Cki1 results in a 3-fold activation in its catalytic rate. This activation may arise from the removal of an inhibitory domain present in the intact enzyme.

Amino Acid Sequence↗

PubMed1994

Budding and fission yeast casein kinase I isoforms have dual-specificity protein kinase activity.

We have examined the activity and substrate specificity of the Saccharomyces cerevisiae Hrr25p and the Schizosaccharomyces pombe Hhp1, Hhp2, and Cki1 protein kinase isoforms. These four gene products are isotypes of casein kinase I (CKI), and the sequence of these protein kinases predicts that they are protein serine/threonine kinases. However, each of these four protein kinases, when expressed in Escherichia coli in an active form, was recognized by anti-phosphotyrosine antibodies. Phosphoamino acid analysis of 32P-labeled proteins showed phosphorylation on serine, threonine, and tyrosine residues. The E. coli produced forms of Hhp1, Hhp2, and Cki1 were autophosphorylated on tyrosine, and both Hhp1 and Hhp2 were capable of phosphorylating the tyrosine-protein kinase synthetic peptide substrate polymer poly-E4Y1. Immune complex protein kinases assays from S. pombe cells showed that Hhp1-containing precipitates were associated with a protein-tyrosine kinase activity, and the Hhp1 present in these immunoprecipitates was phosphorylated on tyrosine residues. Although dephosphorylation of Hhp1 and Hhp2 by Ser/Thr phosphatase had little effect on the specific activity, tyrosine dephosphorylation of Hhp1 and Hhp2 caused a 1.8-to 3.1-fold increase in the Km for poly-E4Y1 and casein. These data demonstrate that four different CKI isoforms from two different yeasts are capable of protein-tyrosine kinase activity and encode dual-specificity protein kinases.

Amino Acid Sequence↗

PubMed1993

Isolation and properties of YCK2, a Saccharomyces cerevisiae homolog of casein kinase-1.

A soluble fragment of YCK2, a casein kinase-1 isoform from Saccharomyces cerevisiae, has been purified and characterized in vitro. The procedure enriches enzyme activity to a final specific activity of 4.7 mumol min-1 mg-1 (when assayed with casein as substrate). Structural analysis reveals that the preparation arises from N-terminal modification and C-terminal proteolysis of the initially synthesized 546-residue protein, consisting of residues 2-495 +/- 1. Kinetic analysis demonstrates that YCK2 is similar to casein kinase-1 isolated from other organisms in its inability to use GTP as nucleotide substrate, in its sensitivity to heparin and ribofuranosyl-benzimidazole inhibitors, and in its peptide substrate selectivity. The enzyme is unusual, however, in that it is insensitive to the potent mammalian casein kinase-1 inhibitor N-(2-aminoethyl)-5-chloroisoquinoline-8-sulfonamide.

Amino Acid Sequence↗

PubMed1992

A solid-phase screen for protein kinase substrate selectivity.

Cassette mutagenesis was used to synthesize an Escherichia coli expression library of unique phosphorylation sites. The cassette encodes a central serine residue surrounded by every combination of Ala, Arg, Gln, Glu, Gly, and Pro residues over a 7-residue segment (a total of 6(7) approximately 2.8 x 10(5) sequences). The cassette was inserted into the gene of a suitable carrier protein and expressed in E. coli with the T7 expression system, and the resultant library was subjected to solid-phase protein phosphorylation assays on nitrocellulose filters. When the library was screened with TPK1 delta, the modified catalytic subunit of the Saccharomyces cerevisiae cAMP-dependent protein kinase, individual colonies that expressed substrates for this kinase were identified. By DNA sequencing through the cassette region of positive clones, the consensus recognition sequence for TPK1 delta was deduced and found to conform with the well-established substrate selectivity of its mammalian homolog (Arg-Arg-Xaa-Ser). Because a large number of clones can be sequenced rapidly, and the positions of invariant residues composing a recognition site identified, this approach may be useful as a general screen of protein kinase substrate selectivity.

Amino Acid Sequence↗

PubMed1992

Two genes in Saccharomyces cerevisiae encode a membrane-bound form of casein kinase-1.

Two cDNAs encoding casein kinase-1 have been isolated from a yeast cDNA library and termed CKI1 and CKI2. Each clone encodes a protein of approximately 62,000 Da containing a highly conserved protein kinase domain surrounded by variable amino- and carboxy-terminal domains. The proteins also contain two conserved carboxy-terminal cysteine residues that comprise a consensus sequence for prenylation. Consistent with this posttranslational modification, cell fractionation experiments demonstrate that intact CKI1 is found exclusively in yeast cell membranes. Gene disruption experiments reveal that, although neither of the two CKI genes is essential by itself, at least one CKI gene is required for yeast cell viability. Spores deficient in both CKI1 and CKI2 fail to grow and, therefore, either fail to germinate or arrest as small cells before bud emergence. These results suggest that casein kinase-1, which is distributed widely in nature, plays a pivotal role in eukaryotic cell regulation.

Amino Acid Sequence↗

PubMed1991

Crystallization and preliminary X-ray analysis of the cAMP-dependent protein kinase catalytic subunit from Saccharomyces cerevisiae.

A truncated variant of TPK1, the yeast cAMP-dependent protein kinase catalytic subunit, was overexpressed in an engineered strain of Saccharomyces cerevisiae, purified by liquid chromatography, and crystallized from solutions of 2-propanol and magnesium at alkaline pH. The crystals are hexagonal dipyramids, space group P6(1)22 (P6(5)22), with unit-cell parameters a = b = 61 A, c = 320 A. Large single crystals suitable for diffraction analysis are obtainable by microseeding, and diffract beyond 2.8-A resolution. Crystal density measurements reveal 12 kinase monomers per unit cell with a single kinase monomer per asymmetric unit.

Base Sequence↗

PubMed1988

Purification and characterization of C1, the catalytic subunit of Saccharomyces cerevisiae cAMP-dependent protein kinase encoded by TPK1.

In the yeast Saccharomyces cerevisiae, three genes TPK1, TPK2, and TPK3 encode catalytic subunits of cAMP-dependent protein kinase. We have purified and characterized the catalytic subunit, C1, encoded by the TPK1 gene. In order to purify C1 completely free of C2 and C3, a strain was constructed that contained only the TPK1 gene and genetic disruptions of the other two TPK genes. The cellular level of C1 was increased by expressing the genes for C1 (TPK1) and yeast regulatory subunit (BCY1) on multiple copy plasmids within this strain. Purification was accomplished by a two-column procedure in which holoenzyme was chromatographed on Sephacryl-200, then bound to an anti-regulatory subunit immunoaffinity column. Pure C1 was released from the antibody column by addition of cAMP. The protein migrated on a sodium dodecyl sulfate-polyacrylamide gel with an Mr of 52,000. Kinetic analysis showed that the apparent Km for ATP and Leu-Arg-Arg-Ala-Ser-Leu-Gly was 33 and 101 microM, respectively. The kcat was determined to be 640 min-1. The protein weakly autophosphorylated, incorporating less than 0.1 mol of phosphate/mol of catalytic subunit. NH2-terminal sequencing revealed that the protein was blocked.

Carrier Proteins↗

PubMed1988

Mutagenesis of the regulatory subunit of yeast cAMP-dependent protein kinase. Isolation of site-directed mutants with altered binding affinity for catalytic subunit.

Oligonucleotide-directed mutagenesis was used to produce mutants in the hinge region of the regulatory subunit (R) of the Saccharomyces cerevisiae cAMP-dependent protein kinase. The mutant proteins were expressed in Escherichia coli, purified, urea treated to produce cAMP-free regulatory (R), and analyzed in vitro for catalytic (C) subunit inhibitory activity in the presence and absence of cAMP. When assayed in the absence of cAMP, wild type R dimer inhibited C with an IC50 of 40 nM. Replacement of amino acid residue Ser-145 (the autophosphorylation site of yeast R) with Ala or Gly produced mutants which were 2-10-fold better inhibitors of C, while replacement with Glu, Asp, Lys, or Thr produced mutants which were 2-5-fold worse inhibitors of C relative to wild type R. When assayed in the presence of cAMP, all R subunits had a decreased affinity for C subunit, with Ser-145 and Thr-145 undergoing autophosphorylation. These results suggest that the amino acid at position 145 of R contributes to R-C interaction and therefore influences the equilibrium of yeast protein kinase subunits in vitro.

Amino Acid Sequence↗

PubMed1988

A mutation in the catalytic subunit of cAMP-dependent protein kinase that disrupts regulation.

A mutant catalytic subunit of adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase has been isolated from Saccharomyces cerevisiae that is no longer subject to regulation yet retains its catalytic activity. Biochemical analysis of the mutant subunit indicates a 100-fold decreased affinity for the regulatory subunit. The mutant catalytic subunit exhibits approximately a threefold increase in Michaelis constant for adenosine triphosphate and peptide cosubstrates, and is essentially unchanged in its catalytic rate. The nucleotide sequence of the mutant gene contains a single nucleotide change resulting in a threonine-to-alanine substitution at amino acid 241. This residue is conserved in other serine-threonine protein kinases. These results identify this threonine as an important contact between catalytic and regulatory subunits but only a minor contact in substrate recognition.

Amino Acid Sequence↗

PubMed1986

Identification of high levels of protein phosphatase-1 in rat liver nuclei.

Rat liver nuclei contain a protein phosphatase that is indistinguishable from the catalytic subunit of protein phosphatase-1 in its molecular mass, sensitivity to inhibitor-1 and inhibitor-2 and specificity for the beta-subunit of phosphorylase kinase. This activity is not bound to the outer nuclear membrane, but located within the nucleus. The average level of protein phosphatase-1 activity in nuclei is at least 5-fold higher than its average extranuclear concentration.

Animals↗

PubMed1986

Identification of the sites on rabbit skeletal muscle protein phosphatase inhibitor-2 phosphorylated by casein kinase-II.

Inhibitor-2 was phosphorylated by casein kinase-II in vitro at a rate similar to that of glycogen synthase, a physiological substrate of this protein kinase. The major phosphorylation sites were identified as serines-86, -120 and -121, the peptide containing serines-120 and -121 being labelled about 2.5-fold more rapidly than that containing serine-86. The 13 residues C-terminal to serine-121 (SGEEDSDLSPEERE) contain seven acidic amino acids, while the six residues following serine-86 (SDTETTE) contain three. These results are consistent with the known specificity requirements of casein kinase-II. The three serines are C-terminal to the threonine (residue 72) whose phosphorylation by glycogen synthase kinase-3 is potentiated by prior phosphorylation with casein kinase-II. This reinforces the view that a C-terminal phosphoserine residue is important for the specificity of glycogen synthase kinase-3. Identification of the residues phosphorylated by casein kinase-II will facilitate further studies on the in vivo phosphorylation state of inhibitor-2.

Amino Acid Sequence↗

PubMed1985

Ca2+/calmodulin-dependent microtubule-associated protein 2 kinase: broad substrate specificity and multifunctional potential in diverse tissues.

In previous studies, we described a soluble Ca2+/calmodulin-dependent protein kinase which is the major Ca2+/calmodulin-dependent microtubule-associated protein 2 (MAP-2) kinase in rat brain [Schulman, H. (1984) J. Cell Biol. 99, 11-19; Kuret, J. A., & Schulman, H. (1984) Biochemistry 23, 5495-5504]. We now demonstrate that this protein kinase has broad substrate specificity. Consistent with a multifunctional role in cellular physiology, we show that in vitro the enzyme can phosphorylate numerous substrates of both neuronal and nonneuronal origin including vimentin, ribosomal protein S6, synapsin I, glycogen synthase, and myosin light chains. We have used MAP-2 to purify the enzyme from rat lung and show that the brain and lung kinases have nearly indistinguishable physical and biochemical properties. A Ca2+/calmodulin-dependent protein kinase was also detected in rat heart, rat spleen, and in the ring ganglia of the marine mollusk Aplysia californica. Partially purified MAP-2 kinase from each of these three sources displayed endogenous phosphorylation of a 54 000-dalton protein. Phosphopeptide analysis reveals a striking homology between this phosphoprotein and the 53 000-dalton autophosphorylated subunit of the major rat brain Ca2+/calmodulin-dependent protein kinase. The enzymes phosphorylated MAP-2, synapsin I, and vimentin at peptides that are identical with those phosphorylated by the rat brain kinase. This enzyme may be a multifunctional Ca2+/calmodulin-dependent protein kinase with a widespread distribution in nature which mediates some of the effects of Ca2+ on microtubules, intermediate filaments, and other cellular constituents in brain and other tissues.

Animals↗

PubMed1985

Multisite phosphorylation of glycogen synthase from rabbit skeletal muscle. Identification of the sites phosphorylated by casein kinase-I.

A casein kinase was highly purified from rabbit skeletal muscle whose substrate specificity and enzymatic properties were virtually identical to those of casein kinase-I from rabbit reticulocytes. Prolonged incubation of glycogen synthase with high concentrations of skeletal muscle casein kinase-I and Mg-ATP resulted in the incorporation of greater than 6 mol phosphate/mol subunit and decreased the activity ratio (+/- glucose-6P) from 0.8 to less than 0.02. The sites phosphorylated by casein kinase-I were all located in the N and C-terminal cyanogen bromide peptides, termed CB-1 and CB-2. At an incorporation of 6 mol phosphate/mol subunit, approximately equal to 2 mol/mol was present in CB-1 and approximately equal to 4 mol/mol in CB-2. Within CB-1, casein kinase-I phosphorylated the serines that were 3, 7 and 10 residues from the N-terminus of glycogen synthase, with minor phosphorylation at threonine-5. Within CB-2, approximately equal to 90% of the phosphate incorporated was located between residues 28 and 53, and at least five of the seven serine residues in this region were phosphorylated. The remaining 10% of phosphate incorporated into CB-2 was located between residues 98 and 123, mainly at a serine residue(s). Two of the major sites labelled by casein kinase-I (serine-3 and serine-10 of CB-1) are not phosphorylated by any other protein kinase. This will enable the role of casein kinase-I as a glycogen synthase kinase in vivo to be evaluated.

Amino Acid Sequence↗