Relationship between the major protein kinase C substrates acidic 80-kDa protein-kinase-C substrate (80K) and myristoylated alanine-rich C-kinase substrate (MARCKS). Members of a gene family or equivalent genes in different species.

Two major protein-kinase-C (PKC) substrates have been described in the literature; an 87-kDa bovine and human PKC substrate, called MARCKS, and an acidic 80-kDa PKC substrate, isolated from rat brain and Swiss 3T3 cells, termed 80K. Since there is only 66-74% sequence similarity between MARCKS and 80K, we have further investigated their relationship in this study. Southern-blot experiments with gene-specific probes demonstrated the presence of the 80K, but not MARCKS, gene in the mouse genome. Furthermore, polymerase-chain-reaction (PCR) analyses using three pairs of primers that specifically recognise either 80K, MARCKS or conserved sequences of both genes, revealed the presence of only the 80K gene in the mouse and rat genomes and only the MARCKS gene in the bovine and human genomes with mRNA expression in the corresponding brain tissues. Northern-blot analysis of a variety of tissues indicated that both 80K and MARCKS have similar patterns of expression. Most components of signal-transduction pathways are present in multiple molecular isoforms as members of a gene family. In contrast, the findings presented in this study indicate that rodent 80K and bovine and human MARCKS are not distinct members of a gene family, but represent the equivalent substrates in different species.     

Identification of three pertussis toxin substrates (41, 40 and 39 kDa proteins) in mammalian brain Comparison of predicted amino acid sequences from G-protein α-subunit genes and cDNAs with partial amino acid sequences from purified proteins

We have determined the partial amino acid sequences of the 40 kDa protein, one of the three pertussis toxin substrates in porcine brain. Purified 40 kDa protein from porcine brain was completely digested with TPCK-trypsin. Digested peptides were separated by reverse-phase HPLC and subjected to analysis by gas-phase protein sequencing. Several sequences of porcine brain 40 kDa protein completely matched with those which were deduced from the nucleotide sequences of the human G_i2α gene and rat G_i2α cDNA. On the other hand, the previously determined sequences of the rat brain 41 and 39 kDa proteins were in complete agreement with the predicted amino acid sequences of rat G_i1α and G_oα cDNAs, respectively.     

Phorbol ester-induced down-regulation of the 80-kDa myristoylated alanine-rich C-kinase substrate-related protein in Swiss 3T3 fibroblasts. Inhibition by staurosporine.

A polyclonal antiserum raised against an oligopeptide with an amino acid sequence corresponding to a sequence of the myristoylated alanine-rich C-kinase substrate (MARCKS) from mouse macrophages and rat brain recognizes the 80-kDa C-kinase substrate from Swiss 3T3 fibroblasts. Using this antiserum for quantitative determination of the 80-kDa MARCKS-related protein, we found that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induces a rapid down-regulation of this protein in the fibroblasts. In accordance with earlier reports, TPA causes phosphorylation of the 80-kDa protein which can be inhibited by staurosporine. Staurosporine also suppresses the TPA-induced down-regulation, possibly indicating that the down-regulation of the MARCKS-related protein is dependent on its phosphorylation by protein kinase C.     

Microtubule-associated protein tau. Identification of a novel peptide from bovine brain

The microtubule-associated protein tau isolated from bovine brain was cleaved with CNBr and the 3 largest peptides of approx. 21, 19 and 18 kDa were obtained. Dephosphorylation of the CNBr digest of tau with alkaline phosphatase changed the electrophoretic mobility of these peptides to 19, 18 and 17 kDa. Amino acid sequencing of the total CNBr digest of tau revealed at least 3 sequences, two of which were highly homologous to previously published mouse and human tau sequences derived from cDNAs. A third amino acid sequence of 17 residues with heterogeneity at position 11 showed no homology with the cDNA-derived tau sequences. These studies suggest that the amino acid sequences of mammalian tau predicted from their cDNAs might be incomplete.     

Purification of a phosphoprotein from rat brain closely related to the 80 kDa substrate of protein kinase C identified in Swiss 3T3 fibroblasts

A phosphoprotein expressed in rat brain is closely related to the 80 kDa substrate of protein kinase C present in 3T3 cells. The protein kinase C substrates from both sources migrate identically on two-dimensional gel electrophoresis and give similar phosphopeptide fragments when digested with protease. Using a series of chromatographic steps, including DEAE-cellulose chromatography, Sephadex G150 gel filtration and reverse phase fast protein liquid chromatography, this phosphoprotein was purified 3800-fold from rat brain. The preparation appears homogenous by one- and two-dimensional gel electrophoresis, is an effective substrate of protein kinase C and contains a high proportion of the acidic amino acids glutamate and aspartate, and of alanine.     

Identification of three pertussis toxin substrates (41, 40 and 39 kDa proteins) in mammalian brain. Comparison of predicted amino acid sequences from G-protein alpha-subunit genes and cDNAs with partial amino acid sequences from purified proteins

We have determined the partial amino acid sequences of the 40 kDa protein, one of the three pertussis toxin substrates in porcine brain. Purified 40 kDa protein from porcine brain was completely digested with TPCK-trypsin. Digested peptides were separated by reverse-phase HPLC and subjected to analysis by gas-phase protein sequencing. Several sequences of porcine brain 40 kDa protein completely matched with those which were deduced from the nucleotide sequences of the human Gi2 alpha gene and rat Gi2 alpha cDNA. On the other hand, the previously determined sequences of the rat brain 41 and 39 kDa proteins were in complete agreement with the predicted amino acid sequences of rat Gi1 alpha and Go alpha cDNAs, respectively.     

Molecular cloning of mouse protein kinase C (PKC) cDNA from Swiss 3T3 fibroblasts

A set of complementary DNAs (cDNAs) that encode the complete 672-amino acid sequence for mouse protein kinase C (PKC) type alpha have been isolated from a mouse Swiss 3T3 cDNA library. Extensive rescreening of this cDNA library only resulted in the isolation of clones of the same PKC species, indicating that Swiss 3T3 fibroblasts express exclusively PKC-alpha. This enzyme is encoded by two different mRNAs that exhibit a substantial heterogeneity in their 3'-noncoding regions. This heterogeneity could have been derived from alternative splicing of the pre-mRNAs or be due to differential usage of the polyadenylation motif. The expression of PKC mRNA in fibroblasts is very low and it is not influenced by treatment with the tumor promoter 12-O-tetradecanoyl-13-phorbol-acetate.     

Peptide phosphorylation by calcium-dependent protein kinase from maize seedlings.

Ca2+-dependent protein kinase (CDPK-1) was purified from maize seedlings, and its substrate specificity studied using a set of synthetic peptides derived from the phosphorylatable sequence RVLSRLHS15VRER of maize sucrose synthase 2. The decapeptide LARLHSVRER was found to be efficiently phosphorylated as a minimal substrate. The same set of peptides were found to be phosphorylated by mammalian protein kinase Cbeta (PKC), but showed low reactivity with protein kinase A (PKA). Proceeding from the sequence LARLHSVRER, a series of cellulose-membrane-attached peptides of systematically modified structure was synthesised. These peptides had hydrophobic (Ala, Leu) and ionic (Arg, Glu) amino acids substituted in each position. The phosphorylation of these substrates by CDPK-1 was measured and the substrate specificity of the maize protein kinase characterised by the consensus sequence motif A/L-5X-4R-3X-2X-1SX+1R+2Z+3R+4, where X denotes a position with no strict amino acid requirements and Z a position strictly not tolerating arginine compared with the other three varied amino acids. This motif had a characteristic sequence element RZR at positions +2 to +4 and closely resembled the primary structure of the sucrose synthase phosphorylation site. The sequence surrounding the phosphorylatable serine in this consensus motif was similar to the analogous sequence K/RXXS/TXK/R proposed for mammalian PKC, but different from the consensus motif RRXS/TX for PKA.     

Abnormal protein kinase C down regulation and reduced substrate levels in non-phorbol ester-responsive 3T3-TNR9 cells.

The cell line TNR9 (E. Butler-Gralla and H. R. Herschman, J. Cell. Physiol. 107:59-67, 1981) in a Swiss 3T3 cell variant that expresses protein kinase C (PKC) but is mitogenically nonresponsive to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). We have found that PKCs purified from variant and parental cells are identical as judged by kinase activity, protease mapping, and column chromatography. We analyzed cellular levels and subcellular location of PKC in TPA-treated 3T3 and TNR9 cells via immunoprecipitation of [35S]methionine-labeled protein and assay of immune-complex PKC kinase activity. TNR9 cells grew to higher densities than parental 3T3 cells. TNR9 cells at maximal density did not down regulate PKC in response to long-term TPA treatment. We compared the 80-kilodalton (kDa) PKC substrate phosphorylation in 3T3 and TNR9 cells by using two-dimensional gels and found that TNR9 cells treated with TPA for 30 min contained only 10 to 15% as much 32Pi associated with the 80-kDa as did parental cells. The TNR9 80-kDa substrate was present at reduced levels compared with the parental-cell 80-kDa substrate as judged by immunoblot and silver staining. Thus, the loss of mitogenic responsiveness to TPA in TNR9 cells is accompanied by resistance to TPA-mediated down regulation of PKC and reduced phosphosubstrate levels.     

The plasma cell membrane glycoprotein, PC-1, is a threonine-specific protein kinase stimulated by acidic fibroblast growth factor.

A 32P-labeled protein that co-purified with acidic fibroblast growth factor (aFGF) receptor from bovine liver proved to be a distinct membrane protein, which itself has kinase activity that is stimulated by aFGF. The protein was designated MAFP for major aFGF-stimulated phosphoprotein. MAFP was purified from bovine liver using immunoaffinity chromatography with monoclonal antibody to MAFP following Triton X-100 extraction of plasma membranes and wheat germ lectin-Sepharose 4B column chromatography. The purified MAFP showed molecular masses of 130 kDa and 260 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions, respectively. Purified MAFP elicited aFGF-stimulated Thr-specific autophosphorylation activity and phosphorylation activity toward protein substrates (myelin basic protein and histone). Amino acid sequence analyses of 16 peptide fragments of MAFP, produced by endoproteinase Lys-C digestion followed by reduction and S-pyridylethylation, showed approximately 80-100% homology with the cDNA-deduced amino acid sequences of human and mouse plasma cell membrane glycoprotein, PC-1 (Buckley, M. F., Loveland, K. A., McKinstry, W. J., Garson, O. M., and Goding, J. W. (1990) J. Biol. Chem. 265, 17506-17511), suggesting that MAFP is the bovine version of PC-1. The amino acid sequences of bovine MAFP, human and mouse PC-1 reveal a putative ATP binding site in their extracellular domains. These results suggest that MAFP(PC-1) is an ectoprotein kinase. In addition to the kinase activity, MAFP(PC-1) was also found to possess alkaline nucleotide phosphodiesterase activity. It is now clear that several of the unique properties previously attributed to the aFGF receptor kinase are actually properties of this novel Thr-specific ectoprotein kinase, which co-purifies with the aFGF receptor and is responsive to stimulation by aFGF.     

Multisite phosphorylation of the 80 kDa (MARCKS) protein kinase C substrate in C3H/10T1/2 fibroblasts. Quantitative analysis of individual sites by solid-phase microsequencing.

A synthetic peptide, KKKKRFSFKKSFKLSGFSFKK, containing the phosphorylation sites of the acidic 80-87 kDa protein kinase C substrate was used to identify phosphopeptides in enzyme digests of this protein from mouse fibroblast C3H/10T1/2 cells. Stimulation of phosphorylation occurred, in vivo, with TPA at Ser7, Ser11 and Ser18, and, with two less potent phorbol esters, at Ser7 and Ser18. Okadaic acid effected a net phosphorylation of Ser7 and/or Ser11. Solid-phase sequencing showed that, in vitro, the order of initial rate of phosphorylation was Ser11 greater than Ser7 greater than Ser18, while Ser18 was preferentially phosphorylated when either Ser7 or Ser11 was occupied. No significant phosphorylation of Ser15 was detected.     

Sequence homologies between p36, the substrate of pp60src tyrosine kinase and a 67 kDa protein isolated from bovine aorta

A 67 kDa actin-binding protein was isolated from bovine aorta. Partial amino acid sequence determination of two large thermolysin peptides were used to compare 67 kDa bovine aorta protein and p36 the substrate of pp60src tyrosine kinase. Sequence analysis shows that 67 kDa bovine aorta protein shares common domains with p36 and possesses the consensus aminoacid sequences of mammalian Ca2+-dependent membrane-binding protein and p36/gelsolin.     

Two human 35 kd inhibitors of phospholipase A2 are related to substrates of pp60v-src and of the epidermal growth factor receptor/kinase

We have purified two 35 kd phospholipase A2 inhibitors from human placenta, which we refer to as lipocortin I and II. Both proteins exhibit similar biochemical properties and occur in placenta at about 0.2% of the total protein. By peptide mapping, sequence, and immunological analyses, we show that lipocortin I and the 35 kd substrate for the EGF-receptor/kinase from A431 cells are the same protein. By similar criteria, we determine that lipocortin II is the human analogue of pp36, a major substrate for pp60src, which has been characterized in chicken embryo fibroblasts and in bovine brush border preparations. The amino acid sequences of lipocortin I and II that we deduced from cDNA clones share 50% homology, indicating that they probably evolved from a common gene.     

Analysis of the genes of the OEE1 and OEE3 proteins of the photosystem II complex from Chlamydomonas reinhardtii

The sequences of the nuclear genes of the 33 kDa (OEE1) and the 16 kDa (OEE3) polypeptides of the oxygen evolving complex of Chlamydomonas reinhardtii have been established. Comparison between the OEE1 protein sequences of C. reinhardtii and higher plants and cyanobacteria reveals 67 and 47% homology. In contrast, C. reinhardtii and higher plants have only 28% overall homology for OEE3 which is mostly limited to the central portion of the protein. The transit peptides of the C. reinhardtii proteins consist of 52 (OEE1) and, most likely, 51 (OEE1) amino acids. They have a basic amino terminal region and, at least in the case of OEE1, a hydrophobic segment at their carboxy terminal end typical of thylakoid lumen proteins. Comparison of the genomic and cDNA clones indicates that the OEE1 and OEE3 genes contain five and four introns, respectively, some of which are located within the coding sequences of the transit peptides.     

Amino acid sequences of peptides from a chymotryptic digest of a urea-soluble protein fraction (U.S.3) from oxidized wool

1. A chymotryptic digest of the protein fraction U.S.3. from oxidized wool was separated into 51 peptide fractions by chromatography on a column of cation-exchange resin. 2. The less acidic fractions were separated into their component peptides by a combination of cation-exchange-resin chromatography, paper chromatography and paper electrophoresis. 3. The amino acid sequences of 34 of these peptides were elucidated, and those of 14 others partially determined. 4. Overlaps between the tryptic and chymotryptic peptides from fraction U.S.3 have enabled ten extended amino acid sequences to be deduced, the longest containing 20 amino acid residues. 5. The relevance of the results to the structures of the helical and non-helical regions of wool is discussed.     

Acidic and basic fibroblast growth factors stimulate tyrosine kinase activity in vivo

We assessed the ability of acidic and basic fibroblast growth factor (FGF) to stimulate tyrosine kinase activity in intact cells. Immunoblot with polyclonal antiphosphotyrosine antibodies detected a 90-kDa phosphotyrosine-bearing protein in lysates of Swiss 3T3 cells exposed to pituitary-derived FGF, recombinant acidic FGF, or recombinant basic FGF, but not from unstimulated cells or cells exposed to epidermal growth factor or platelet-derived growth factor. Phosphotyrosine and its analogue phenyl phosphate, but not phosphoserine, phosphothreonine, or tyrosine itself, blocked recognition of the 90-kDa protein by antiphosphotyrosine antiserum. A monoclonal antiphosphotyrosine antibody also recognized the 90-kDa protein and was used to partially purify the protein by immunoaffinity chromatography. Phosphoamino acid analysis of the 90 kDa band revealed that it contained 20% phosphotyrosine, 35% phosphothreonine, and 45% phosphoserine. Tyrosine phosphorylation of the 90-kDa protein was detectable within 30 s and reached a plateau within 10 min of FGF addition. The addition of suramin, which blocks the interaction of FGF with its receptor, caused rapid disappearance of the 90 kDa band. Cell fractionation experiments were consistent with the 90-kDa protein being membrane-associated, but cross-linking studies revealed that the FGF receptor had an Mr between 145 and 210 kDa in Swiss 3T3 cells, distinct from the 90-kDa major substrate for tyrosine phosphorylation. These data demonstrate that both acidic and basic FGF activate a tyrosine kinase in vivo leading to phosphorylation of a unique 90-kDa substrate, and they suggest that protein modification by phosphorylation at tyrosine is involved in eliciting the mitogenic effect of FGF.     

Purification and characterization of aromatase from human placenta

Aromatase from human placenta has been purified to homogeneity (MW 55,000). Enzymatic activity can be reconstituted with reductase from pig liver in an aqueous buffer or after incorporation of the enzyme into liposomes. In both cases the enzyme converts androstenedione to estrone and testosterone to estradiol. Aromatase shows a typical CO-spectrum when reduced with dithionite and a type I spectral shift with both substrates. The NH2 terminal amino acid sequence is hydrophobic but shows no homology to that of other cytochromes P-450. Five cysteine peptides have been isolated by HPLC following tryptic digestion of the [14C]-carboxymethylated protein. Amino acid sequences of these peptides reveal that histidine is the carboxy-terminal amino acid of the protein and that significant homology exists with corresponding peptides from other cytochromes P-450. Unique oligonucleotides (62 and 30 MER) synthesized on the basis of a 45 amino acid sequence near the center of the molecular have been used to clone the aromatase gene from a cDNA expression library from human placenta in lambda gt11.