Molecular comparison of alpha 2-adrenergic receptors from rat adrenocortical carcinoma and human blood platelet

We have previously described a simple two-step purification technique to isolate alpha 2-adrenergic receptors from the rat adrenocortical carcinoma (Jaiswal, R. K. and Sharma, R. K. (1985) Biochem. Biophys. Res. Commun. 130, 58-64). Utilizing this technique we have now achieved approximately 77,000-fold purification to apparent homogeneity of alpha 2-adrenergic receptors from human platelets. We have compared the biochemical characteristics of these receptors with those from the rat, which were purified approximately 40,000-fold to homogeneity. The [125I] receptor proteins from two sources showed: (a) a single radioactive band with a Mr of 64,000 as evidenced by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE); and (b) a single symmetrical peak with a pI of 4.2 by isoelectric focusing polyacrylamide gel electrophoresis. Both proteins showed typical alpha 2-adrenergic binding characteristics with specific binding activities of 13.85 nmol/mg and 14.17 nmol/mg protein. These values are close to the theoretical binding activity of 15.6 nmol/mg protein for 1 mol of the ligand binding 1 mol of the receptor protein. These results attest to the purity of the receptors, to its Mr of 64,000, and to its acidic nature. However, the peptide maps of the radioiodinated alpha 2-adrenergic receptors from rat adrenocortical carcinoma and human blood platelets reveal some distinct differences which may relate to the differences in the pharmacological specificities between rodent and non-rodent alpha 2-adrenergic receptors.

The cell-cycle regulated proliferating cell nuclear antigen is required for SV40 DNA replication in vitro

Cell-free extracts prepared from human 293 cells, supplemented with purified SV40 large-T antigen, support replication of plasmids containing the SV40 origin of DNA replication. A cellular protein (Mr approximately 36,000) that is required for efficient SV40 DNA synthesis in vitro has been purified from these extracts. This protein is recognized by human autoantibodies and is identified as the cell-cycle regulated protein known as proliferating cell nuclear antigen (PCNA) or cyclin.

Comparative biological properties of lamprey gonadotropin-releasing hormone in vertebrates

The biological activities of lamprey GnRH were determined in the lamprey, chicken, sheep, and rat. Lamprey GnRH elevated plasma steroid levels and stimulated ovulation in the lamprey, but had little or no LH-releasing activity in chicken and sheep pituitary bioassays or effect on GnRH receptor-binding activity in the rat pituitary. The lamprey GnRH molecule is structurally distinct from other known vertebrate GnRHs and is the first identified molecule in this family to have different amino acids in the third and sixth positions. These data suggest that the presence of Tyr3 or Glu6 in lamprey GnRH may account for the lack of biological activity in the representatives of the two different vertebrate classes investigated in this study.

Structural evidence that endothelial cell growth factor beta is the precursor of both endothelial cell growth factor alpha and acidic fibroblast growth factor

Two endothelial cell growth factors (ECGF) have been purified from bovine brain and termed alpha- and beta-ECGF [Burgess, W. H., Mehlman, T., Friesel, R., Johnson, W. V. & Maciag, T. (1985) J. Biol. Chem. 260, 11389-11392]. Amino acid sequence analysis indicates that beta-ECGF represents a 20 amino acid amino-terminal extension of alpha-ECGF and a 14 amino acid amino-terminal extension of acidic fibroblast growth factor. These data indicate that both alpha-ECGF and acidic fibroblast growth factor may be derived from beta-ECGF by posttranslational processing. Analysis of the amino-terminal 14 residues of beta-ECGF by fast-atom-bombardment mass spectrometry established the amino acid sequence of this region and the identity of the blocking group at the amino terminus (acetyl).

Primary structure of gonadotropin-releasing hormone from lamprey brain

The primary structure of gonadotropin-releasing hormone (GnRH) isolated from whole brains of lamprey is pGlu-His-Tyr-Ser-Leu-Glu-Trp-Lys-Pro-Gly-NH2. This unique decapeptide was isolated and purified from brain extracts by reverse-phase high performance liquid chromatography. The structure of the peptide was established from chymotryptic fragments that were identified by protein sequence analysis and fast atom bombardment mass spectrometry. The peptide reacts with an antiserum raised against mammalian GnRH and is structurally identified as a member of the GnRH family by the amino and carboxyl termini of pGlu1-His2 and Pro9-Gly10NH2, the conservation of Ser4 in the internal segment of the molecule and its length of 10 amino acids. For the first time, amino acid substitutions are found in positions 3 and 6, critical for biological potency and conformation, respectively. Additionally, a second form of GnRH (lamprey II GnRH), representing about 10% of the total GnRH immunoreactive material in the brain, was isolated; its amino acid composition differs by 3 residues from lamprey I GnRH. Synthetic lamprey I GnRH elevates plasma estradiol in adult female lampreys.

Structural and immunological characterization of the amino-terminal domain of mammalian neural cell adhesion molecules

The neural cell adhesion molecules (N-CAMs) are a group of structurally and immunologically related glycoproteins found in vertebrate neural tissues. Adult brain N-CAMs have apparent molecular weights of 180,000 and 140,000 with an additional form at 120,000 in murine brain. In embryonic brain, N-CAMs are represented by a highly sialylated form with an apparent molecular weight greater than 180,000. We have used monoclonal antibodies that cross-react with N-CAMs of various mammalian species to purify N-CAMs from adult murine and bovine brains and from embryonic murine brains. We determined the amino acid sequences of the amino-terminal domains of these molecules: Leu-Gln-Val-Asp-Ile-Val-Pro-Ser-Gln-Gly-Glu-Ile-Ser-Val-Gly-Glu-Ser. This sequence is highly conserved among all three forms of adult murine brain N-CAM as well as embryonic murine brain N-CAM and adult bovine brain N-CAM. Based on this sequence, we synthesized an undecapeptide and used it to raise a site-directed polyclonal antiserum. This antiserum reacted with the intact N-CAM in liquid phase radioimmunoassays, immunoblotting experiments, and immunofluorescent labeling of cells. The antiserum also reacted with N-CAMs in extracts of brain tissues from different species, confirming the highly conserved nature of the amino-terminal domain of mammalian N-CAMs. Immunofluorescence experiments indicated that this domain resides on the outer surfaces of cells that express N-CAMs, in both primary neuronal cell culture and in cell lines.

Purification and characterization of a neurite extension factor from bovine brain

The extension of neurites by chicken embryo cerebral cortical neurons can be measured quantitatively at low cell density in serum-free, defined medium. An acidic, heat-stable protein fraction from bovine brain has been shown to have neurite extension activity in this assay. We report the use of reversed-phase HPLC to purify a neurite extension factor from this fraction to apparent homogeneity. The protein was characterized by NaDodSO4/PAGE. In the presence of reducing agents, the protein migrated as a single band, with an apparent molecular weight of 6500. In the absence of reducing agents, the protein showed bands at apparent molecular weights of 6500, 21,000-22,000, 30,000, and 40,000. Reduction and S-carboxymethylation of the protein abolished all biological activity and resulted in a shift of the apparent molecular weight to 11,000. The amino acid composition of the purified neurite-extension factor was nearly identical to that of bovine brain S100 beta. The amino acid sequences of peptides derived from trypsin or cyanogen bromide digests of the protein were identical to those found in S100 beta and accounted for 71 of 91 amino acids in the protein. However, three peptides obtained from cyanogen bromide digestion of the nonreduced protein appeared to be disulfide-linked dimers. Our results indicate that a biological activity, neurite extension, which is critical for the development of the nervous system, is associated with a disulfide form of S100 beta.

Characterization of human brain S100 protein fraction: amino acid sequence of S100 beta

Two major components of human brain S100 fraction were purified by HPLC and an amino acid sequence was elucidated for the S100 beta component. Human S100 proteins showed absorption spectra and amino acid compositions similar to S100 alpha and S100 beta from bovine brain. However, the relative amounts of the human proteins were 4% S100 alpha and 96% S100 beta by weight, while the bovine protein distribution was 47% S100 alpha and 53% S100 beta by weight. An amino acid sequence of human S100 beta was established by analysis of overlapping fragments generated by cyanogen bromide and trypsin cleavage. Three amino acid sequence differences between the human and bovine S100 beta were found at residues 7, 62, and 80. These differences were chemically conservative and compatible with minimum single base changes in the codon structures. These results document that S100 beta is a conserved protein among mammals and provide the necessary foundation for current clinical studies.

Structural characterization of the calcium binding protein s100 from adipose tissue

A partial amino acid sequence for bovine adipose tissue S100 was elucidated by characterization of peptides generated by cyanogen bromide cleavage. The cyanogen bromide peptides were aligned by homology with the bovine brain S100 beta sequence. The results demonstrate that adipose S100 beta is probably identical to brain S100 beta, and suggest that S100 beta is a conserved protein among tissues of the same species.

Drug-protein interactions: isolation and characterization of covalent adducts of phenoxybenzamine and calmodulin

Phenoxybenzamine, an alpha-adrenergic antagonist containing a (chloroethyl)amine group, labels calmodulin in the presence of calcium. The covalent interaction is inhibited by chlorpromazine in a concentration-dependent manner. Adducts of calmodulin and phenoxybenzamine were separated by high-performance liquid chromatography into four major fractions: two containing 0.6 and 1.2 mol of drug per mol of protein and two different fractions each containing 2.0 mol/mol. Each adduct had a reduced ability to activate cyclic nucleotide phosphodiesterase and myosin light chain kinase, and the chlorpromazine binding capacities of the phenoxybenzamine-calmodulin adducts were diminished to the extent of phenoxybenzamine incorporation into each adduct. Isolation and characterization of labeled peptides from phenoxybenzamine-modified calmodulins indicated that peptides encompassing residues 38-75, 107-126, and 127-148 contained phenoxybenzamine label. These studies directly demonstrate the relatedness between the binding activities of two structurally dissimilar calmodulin antagonists, demonstrate that covalent adducts of calmodulin and drugs with equal stoichiometries of labeling can have quantitative differences in activity and sites of modification, and provide direct evidence of distinct drug binding regions in calmodulin located in the amphipathic alpha-helical regions of the second and fourth domains.

Drug-protein interactions: binding of chlorpromazine to calmodulin, calmodulin fragments, and related calcium binding proteins

The quantitative binding of a phenothiazine drug to calmodulin, calmodulin fragments, and structurally related calcium binding proteins was measured under conditions of thermodynamic equilibrium by using a gel filtration method. Plant and animal calmodulins, troponin C, S100 alpha, and S100 beta bind chlorpromazine in a calcium-dependent manner with different stoichiometries and affinities for the drug. The interaction between calmodulin and chlorpromazine appears to be a complex, calcium-dependent phenomenon. Bovine brain calmodulin bound approximately 5 mol of drug per mol of protein with apparent half-maximal binding at 17 microM drug. Large fragments of calmodulin had limited ability to bind chlorpromazine. The largest fragment, containing residues 1-90, retained only 5% of the drug binding activity of the intact protein. A reinvestigation of the chlorpromazine inhibition of calmodulin stimulation of cyclic nucleotide phosphodiesterase further indicated a complex, multiple equilibrium among the reaction components and demonstrated that the order of addition of components to the reaction altered the drug concentration required for half-maximal inhibition of the activity over a 10-fold range. These results confirm previous observations using immobilized phenothiazines [Marshak, D.R., Watterson, D.M., & Van Eldik, L.J. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6793-6797] that indicated a subclass of calcium-modulated proteins bound phenothiazines in a calcium-dependent manner, demonstrate that the interaction between phenothiazines and calmodulin is more complex than previously assumed, and suggest that extended regions of the calmodulin molecule capable of forming the appropriate conformation are required for specific, high-affinity, calcium-dependent drug binding activity.

Structural and functional properties of calmodulin from the eukaryotic microorganism Dictyostelium discoideum

Calmodulin was purified from the eukaryotic microorganism Dictyostelium discoideum and characterized in terms of its nearly complete primary structure and quantitative activator activity. The strategy for amino acid sequence analysis took advantage of the highly conserved structure of calmodulin and employed a new procedure for limited cleavage of calmodulin that uses a protease from mouse submaxillary gland. Fourteen amino acid sequence differences between Dictyostelium and bovine calmodulin were identified unequivocally, as well as an unmethylated lysine at residue 115 instead of N epsilon, N epsilon, N epsilon-trimethyllysine. Seven of the amino acid substitutions in Dictyostelium calmodulin are novel in that the residues at these positions are invariant in all calmodulin sequences previously examined, most notably an additional residue at the carboxy terminus. Comparison of the Dictyostelium calmodulin sequence with other calmodulin sequences shows that the region with the greatest extended sequence identity includes parts of the first and second structural domains and the interdomain region between domains 1 and 2. Dictyostelium calmodulin activated bovine brain cyclic nucleotide phosphodiesterase in a manner indistinguishable from that of bovine brain calmodulin. However, Dictyostelium calmodulin activated pea NAD kinase to a maximal level 4.6-fold greater than that produced by bovine brain calmodulin. This functional difference demonstrates the potential biological importance of the limited number of amino acid sequence differences between Dictyostelium calmodulin and other calmodulins and provides further insight into the structure, function, and evolution of the calmodulin family of proteins.

Calcium-dependent interaction of S100b, troponin C, and calmodulin with an immobilized phenothiazine

We have purified the brain-specific protein S100b by affinity-based adsorption chromatography on phenothiazine-Sepharose conjugates and studied the interaction of this and other calcium-modulated proteins with the immobilized antipsychotic drug. Bovine brain calmodulin, rabbit skeletal muscle troponin C, and bovine brain S100b bind to phenothiazine-Sepharose in a calcium-dependent manner. These three proteins competitively inhibit the calcium-dependent binding of 125I-labeled chicken gizzard calmodulin to the immobilized drug. However, carp parvalbumin and chicken intestinal vitamin D-dependent calcium binding protein do not inhibit the phenothiazine--calmodulin interaction. These results suggest that the known amino acid sequence homology among calmodulin, troponin C, and S100b may be reflected in a similar functional domain present in these proteins but absent in parvalbumin and vitamin D-dependent protein.

The site of alpha-chymotryptic activation of pigeon erythrocyte adenylate cyclase

Treatment of intact pigeon erythrocytes with trypsin or alpha-chymotrypsin does not alter the isoproterenol-dependent adenylate cyclase activity in plasma membranes prepared after proteolysis. However, both proteases affect adenylate cyclase activity when isolated membranes are digested. Thus, the proteases probably act at the cytoplasmic side of the membranes. This conclusion is supported by the finding that proteases are able to inhibit NADH cytochrome c oxidoreductase, an enzyme located on the inner face of the plasma membrane. In isolated membranes, trypsin inhibits adenylate cyclase. Chymotrypsin (2.5 microgram/ml, 10 min, 37 degrees C) activates adenylate cyclase about 3-fold when the enzyme activity is measured with NaF, guanosine 5'-(beta, gamma-imino)-triphosphate, or guanosine 5'-(beta, gamma-imino)-triphosphate and isoproterenol. Chymotrypsin also activates adenylate cyclase in membranes pretreated with cholera toxin. Activation by chymotrypsin is not expressed when adenylate cyclase is assayed with 5 mM Mn2+ without guanine nucleotides or fluoride. However, the chymotryptic activation is expressed when guanosine 5'-(beta, gamma-imino)-triphosphate is present together with Mn2+. We conclude that interaction of the guanine nucleotide regulatory subunit with the catalytic subunit of adenylate cyclase is required for expression of chymotryptic activation.