The subunit structure of bovine brain 14-3-2

Two aspects of the subunit structure of the bovine brain specific protein 14-3-2 have been examined. On the one hand, native 14-3-2 has been separated into two fractions by hydroxylapatite chromatography. One eluted at the same position when chromatographed on the same column, while the other redistributed into the same two fractions again. Amino acid analysis of these two forms of 14-3-2 gave results that were not significantly different under the condition of analysis. Furthermore, when each peak was subjected to cyanogen bromide cleavage, very similar elution profiles of the resultant fragments were obtained. The two pools also cross-reacted with antiserum to 14-3-2. Reaction of purified 14-3-2 with dimethylsuberimidate caused the formation of covalently bound protein units of 100,000 molecular weight when measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis, as opposed to the 50,000 minimal molecular weight normally detected. On the other hand, analysis of the soluble tryptic peptides of S-[14C]carboxymethyl 14-3-2 yielded only three distinct radioactive peptides, each with one residue of S-carboxymethylcysteine whereas 8 are expected on the basis of the amino acid composition of the 50,000 molecular weight polypeptide chains. Thermolysin digestion of a similarly modified 14-3-2 preparation yielded all of the radioactivity in 5 S-carboxymethylcysteine-containing peptides. The partial amino acid sequence of these peptides indicates that they represent 4 unique areas of the polypeptide chain. Since 8 such peptides were expected, that is, double the number found, the minimum structural unit of the protein must be of 25,000 molecular weight. The results of these experiments do not permit distinction between a duplication of the structure within a single polypeptide chain or the alternate possibility of two polypeptide chains bound by unusually strong non-covalent bonds. These results suggest that 14-3-2 is a covalently linked dimer of 25,000 mol.wt. units that can aggregate to form larger species of 100,000 mol.wt. and higher.     

Specific photoaffinity labeling of Tyr-49 on the light chain in the steroid-combining site of a mouse monoclonal anti-estradiol antibody using two epimeric 6alpha- and 6beta-(5-azido-2-nitrobenzoyl)amidoestradiol photoreagents

A mouse monoclonal anti-7-(O-carboxymethyl)oximinoestradiol antibody was photoaffinity labeled with two cross-reactive 6alpha- and 6beta-(5-azido-2-nitrobenzoyl)amido[17alpha-3H]estradiol photoreagents (6alpha- and 6beta-ANBA-[17alpha-3H]estradiol). Covalently bound radioactivity was found exclusively on the light chain. The maximal level of specific incorporation was 0.18 mol of label per mole of antibody for both photoreagents. In both cases, tryptic digestion of the photolabeled light chain, immunopurification with the immobilized antibody, reverse-phase liquid chromatography, and Edman degradation showed the presence of radioactive peptide GLM-([3H]X)-HGNTLEDGIPSR derived from peptide 46-61 of the light chain sequence (determined from cDNA) in which the unidentified amino acid corresponding to X is a Tyr residue. Two other radioactive peptides were also isolated, one corresponding probably to the methionine sulfoxide derivative of the peptide 46-61 photolabeled with the 6beta-reagent and the other to the N-terminal tetrapeptide 46-49 of the peptide 46-61 photolabeled with the 6alpha-reagent. In all cases, the main peak of radioactivity was released at the fourth Edman cycle, thus suggesting that the same Tyr-49 residue on the light chain was photolabeled. This residue is contiguous to the N-terminal amino acid of the second hypervariable complementary determining region 50-56 of light chain. Covalent labeling was confirmed by mass spectrometry of photolabeled peptides which showed molecular ion values corresponding to the addition of the photoactive 6alpha- or 6beta-ANBA-estradiol nitrene derivatives to the peptide.     

Discriminable stimuli produced by hallucinogens

Bison pancreatic ribonuclease was isolated by affinity chromatography. Thermolysin and tryptic digestion of denaturated protein, and subtilisin digestion of native protein yielded peptides, which were purified and submitted to amino acid analysis. These peptides, together with partial sequence data obtained by Stewart & Stevenson (16) overlap the entire amino acid sequence of bison ribonuclease. No differences with bovine ribonuclease were found, although there may be differences in state of amidation of some residues.     

Hemoglobin Dakar = Hb Grady: demonstration by a new approach to the analysis of the tryptic core region of the alpha chain and oxygen equilibrium properties

Preliminary studies have suggested that in Hb Dakar, histidine alpha112 was substituted by a glutamine. A re-investigation on this hemoglobin is presented in this report. A structural study has been performed using a new approach to analyse the tryptic core region of the human hemoglobin alpha chain. After tryptic digestion of the aminoethylated alpha chain, a secondary digestion of the tryptic core was carried out with chymotrypsin and with another protease, thermolysin. Analyses of the chymotryptic and thermolytic peptides indicated that the structure of Hb Dakar was identical to that of Hb Grady previously described by Huisman et al. who showed the insertion of three amino acid residues in position alpha115 or alpha118. The insertion, which was localized near two residues involved in the alpha1beta1 contact, did not produce a dissociation into dimers. Functional studies demonstrated a a slightly increased oxygen affinity, a lowered cooperativity and a normal Bohr effect. The low amount of the abnormal hemoglobin (8%) may in part be explained by a slight instability of the molecule.     

Studies on subcellular fractions of human platelets by the lactoperoxidase-iodination technique

The iron-saturated and iron-free (apo) forms of bovine transferrin and lactoferrin were digested with trypsin and the digests analysed by column chromatography and electrophoresis. Both of the iron-saturated proteins were more resistant to proteolysis than the corresponding apoproteins, and iron-transferrin was more resistant than iron-lactoferrin. Digestion of iron-transferrin yielded two iron-binding fragments with molecular weights of 32 000 and 38 500 whereas apotransferrin yielded only the larger fragment. In digests of lactoferrin, up to five different fragments with molecular weights ranging from 25 000 to 52 700 were detected, there being no obvious qualitative difference between digests of iron-lactoferrin and apolactoferrin. The susceptibility of apolactoferrin to tryptic digestion was only slightly reduced when apolactoferrin was complexed with beta-lactoglobulin, suggesting that complex-formation is not a mechanism for protecting lactoferrin against intestinal degradation. There was no immunological cross reaction between bovine transferrin or its digestion products against anti-lactoferrin antiserum, or vice-versa.     

Nucleotide binding to autotaxin: crosslinking of bound substrate followed by lysC digestion identifies two labeled peptides

Autotaxin (ATX) is a 125 kDa glycoprotein motility factor and exoenzyme which can catalyze the hydrolysis of either the alpha-beta or at the beta-gamma phosphodiester bond in ATP. Its motility stimulating activity requires an intact 5'-nucleotide phosphodiesterase (PDE) active site. Photolysis-dependent labeling of ATX with alpha-[32P]-8-N3-ATP, lysC digestion, and peptide HPLC resolved two radioactive fractions containing single peptides whose amino-terminal sequences were determined. Peptide A (T210FPNLYTLATG. . .) was derived from the PDE active site and peptide B (Y318GPFGPEMTNP. . .) was not previously known to be involved in any of the activities of ATX. The differential effect of NaCl concentration on the labeling of these two peptides, as well as on the two reaction types catalyzed by ATX, allows a classification of activities which predicts both the position of preferential peptide labeling by bound ATP and also the position of phosphodiester bond hydrolysis.     

RP-HPLC binding domains of proteins

Procedures have been developed to identify the chromatographic binding domains of horse heart cytochrome c (Cyt c) and bovine growth hormone (bGH) during their interaction with reversed-phase sorbent materials. The procedure involves adsorption of the protein solute to the chromatographic sorbent, followed by proteolytic cleavage. Comparison of the proteolytic map obtained for Cyt c and bGH in free solution with the corresponding map obtained when these proteins are adsorbed to the chromatographic sorbent revealed significant differences in the digestion pattern. Following characterization of the peptides generated in both maps, the results indicated that specific regions on the surface of both Cyt c and bGH are inaccessible to tryptic cleavage when adsorbed to the hydrophobic surface of both a C-4 and a C-18 sorbent. Based on the assumption that the region of the protein surface that is in contact with the sorbent remains intact and bound to the sorbent during the digestion step, while the protein surface that is exposed to the solvent is accessible to proteolysis, the regions that were inaccessible to tryptic digestion were found to correspond to hydrophobic domains on the protein surface. These results also suggest that the three-dimensional structures of these proteins remain largely intact upon adsorption to the hydrophobic surface.     

Effect of cholecystokinin-pancreozymin (CCK-PZ) on glycoprotein secretion from mouse gallbladder epithelium: an ultrastructural and cytochemical study

L-Azetidine-2-carboxylic acid, the naturally occurring lower homologue of L-proline, is incorporated into hemoglobin S (sickle hemoglobin) in vitro. Sickle erythrocytes from patients with sickle cell anemia incubated with L-[3H] azetidine-2-carboxylate synthesized radiolabeled hemoglobin which when isolated from cell lysates, co-chromatographed with hemoglobin S on DEAE-cellulose columns. The alpha/beta ratio of azetidine carboxylate incorporation into the globin chains of sickle hemoglobin was 0.94, which is consistent with the presence of four proline residues in each polypeptide chain. Incorporation of azetidine carboxylate into hot trichloroacetic acid-insoluble material in sickle erythrocytes indicated that the homologue was present in the polypeptide backbone of the globin chains of sickle hemoglobin. Amino acid analysis of the hot trichloroacetic acid-insoluble material from sickle erythrocytes which had been incubated with radiolabeled azetidine carboxylate indicated that 75% of the radioactivity could be accounted for as intact homologue while 20% of the radioactivity co-chromatographed with alanine. These results suggest that azetidine carboxylate is incorporated unaltered into hemoglobin S in addition to being metabolized to alanine in sickle erythrocytes prior to incorporation into protein. The kinetics of thermal precipitation of hemoglobin S (oxygen ligand) into which radioactive azetidine carboxylate or radioactive proline had been incorporated in vitro is identical. This observation, together with the behavior of hemoglobin S and the globin chains from hemoglobin S containing azetidine carboxylate during ion-exchange chromatography, indicates that homologue replacement of prolyl residues does not significantly alter the overall charge or stability of the hemoglobin S tetramer. Azetidine carboxylate did not inhibit uptake of radiolabeled proline by sickle erythrocytes suggesting that the homologue does not adversely affect amino acid transport in these cells.     

Lysine 207 as the site of cross-linking between the 3'-end of Escherichia coli initiator tRNA and methionyl-tRNA formyltransferase

The specific formylation of initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is important for initiation of protein synthesis in Escherichia coli. In attempts to identify regions of MTF that come close to the 3'-end of the tRNA, we oxidized 32P-3'-end-labeled E. coli initiator methionine tRNA with sodium metaperiodate and cross-linked it to MTF. The cross-linked MTF was separated from uncross-linked MTF by DEAE-cellulose chromatography, and the tRNA in the cross-linked MTF was hydrolyzed with nuclease P1 and RNase T1, leaving behind an oxidized fragment of [32P]AMP attached to MTF. Trypsin digestion of the cross-linked MTF followed by high pressure liquid chromatography of the digest yielded two peaks of radioactive peptides, I* and II*. These peptides were characterized by N- and/or C-terminal sequencing and by matrix-assisted laser desorption ionization mass spectroscopy. Peptide I* contained amino acids Gln186-Lys210 with Lys207 as the site of the cross-link. Peptide II*, a partial digestion product, contained amino acids Gln186-Arg214 also with Lys207 as the site of the cross-link. The molecular masses of peptides I* and II* indicate that the final product of the cross-linking reaction between the periodate-oxidized AMP moiety of the tRNA and Lys207 is most likely a morpholino derivative rather than a reduced Schiff's base.     

A single histidine is required for activity of cytochrome c peroxidase from Paracoccus denitrificans

The diheme cytochrome c peroxidase from Paracoccus denitrificans was modified with the histidine-specific reagent diethyl pyrocarbonate. At low excess of reagent, 1 mol of histidine was modified in the oxidized enzyme, and modification was associated with loss of the ability to form the active state. With time, the modification reversed, and the ability to form the active state was recovered. The agreement between the spectrophotometric measurement of histidine modification and radioactive incorporation using a radiolabeled reagent indicated little modification of other amino acids. However, the reversal of histidine modification observed spectrophotometrically was not matched by loss of radioactivity, and we propose a slow transfer of the ethoxyformyl group to an unidentified amino acid. The presence of CN- bound to the active peroxidatic site of the enzyme led to complete protection of the essential histidine from modification. Limited subtilisin treatment of the native enzyme followed by tryptic digest of the C-terminal fragment (residues 251-338) showed that radioactivity was located in a peptide containing a single histidine at position 275. We propose that this conserved residue, in a highly conserved region, is central to the function of the active mixed-valence state.     

3H](azidophenyl)ureido taxoid photolabels peptide amino acids 281-304 of alpha-tubulin

The taxoid binding site on porcine brain tubulin was covalently labeled, in the presence or absence of Taxotere, with the photoaffinity reagent [3H]-p-(azidophenyl)ureido taxoid derivative [3H]TaxAPU [Combeau, C., Commercon, A., Mioskowski, C., Rousseau, B., Aubert, F., & Goeldner, M. (1994) Biochemistry 33, 6676-6683]. After disulfide reduction and carboxymethylation, the alkylated tubulin samples were treated with trypsin and the mixtures of peptides were first fractionated by gel filtration over Sephadex G50. Anion exchange chromatography of the radioactive areas showed, for one area, three major radioactive signals which were further analyzed by reversed phase C18 HPLC, leading to well-resolved radioactive peaks. Microsequencing of these different peaks gave a complete sequence of a tryptic fragment on alpha-tubulin (alpha-281-304) and two partial peptide sequences of a tryptic fragment on beta-tubulin (beta-217-229) in addition to sequences of mixture of peptides. The radioactive signals were lost while concentrating the samples for microsequencing, preventing the identification of the modified amino acids. These results identify the first peptide on alpha-tubulin which binds to the taxoids and confirm the involvement of both alpha- and beta-tubulin in the taxoid binding site.     

Haemoglobins of the shark, Heterodontus portusjacksoni II. Amino acid sequence of the alpha-chain

The amino acid sequence of the alpha-chain of the principal haemoglobin from the shark, H. portusjacksoni has been determined. The chain has 148 residues and is acetylated at the amino terminal. The soluble peptides obtained by tryptic and chymotryptic digestion of the protein or its cyanogen bromide fragments were isolated by gel filtration, paper ionophoresis and paper chromatography. The amino acid sequences were determined by the dansyl-Edman procedure. The insoluble "core" peptide from the tryptic digestion contained 34 residues and required cleavage by several prosteases before the sequence was established. Compared with human alpha-chain there are 88 amino acid differences including the additional seven residues which appear on the amino terminal of the shark chain. There is also one deletion and one insertion. The chain contains no tryptophan but has four cysteinyl residues which is the highest number of such residues recorded for a vertebrate globin. In the alpha1beta1 contact sites there are four changes in the oxyhaemoglobin form and six deoxy form. Nine of the 16, alpha1beta1 contact sites show variation while three of the haem contact sites have changed in comparison to the residues known to be involved in these interactions in horse haemoglobin alpha-chain. Use of the sequence data to estimate a time of divergence of the shark from the main vertebrate line yielded the value of 410 +/- 46 million years. The data, in general, support the palaeontological view that bony fishes arose before the elasmobranchs.     

Macromolecular interactions of [14C-ring]melphalan in blood

The pharmacokinetics and macromolecular interactions of [14C-ring]melphalan (L-PAM) in blood were studied in rats following a single oral dose (20 mg/kg, 0.1 mCi/kg). Radioactivity levels were monitored in blood over a period of 72 hr. The highest levels of radioactivity were observed at 2 hr. The decline of radioactivity from the blood was biphasic with T1/2 alpha = 7 hr and T1/2 beta = 75 hr. The radioactive species in plasma corresponded to unchanged L-PAM and its two known hydrolytic products 4,2-hydroxyethyl 2-chloroethylamino-L-phenylalanine (L-MOH) and 4-[bis(2-hydroxyethyl)amino]-L-phenylalanine (L-DOH). In addition, four other major, previously unknown, metabolites of L-PAM were detected in plasma. At 72 hr, most of the radioactivity was bound to macromolecular components, 26% to plasma macromolecules and 62% in red blood cells. Covalent binding to blood cells was mainly to membrane proteins. Binding to hemoglobin and other soluble components of the red cells was also observed, with a 5000-fold greater affinity for membranes. These studies suggest extensive interaction of melphalan, or its metabolites, with membrane and soluble proteins of red blood cells.     

Primary structure of chicken cardiac myosin S-1 heavy chain

The sequence of the NH2-terminal 830 amino acid residues of chicken cardiac ventricular muscle myosin subfragment-1 (S-1) was determined. S-1 was obtained by limited chymotryptic digestion, and cleaved into three characteristics fragments (23, 41, and 22 kDa fragments) by limited tryptic digestion. These fragments were isolated by gel filtration on a Sephadex G-100 column, followed by cation-exchange chromatography on a CM-52 column and reverse-phase HPLC. The isolated fragments were sequenced completely. Peptides overlapping the 23 and 41 kDa fragments and also overlapping the 41 and 22 kDa fragments were obtained by cleaving S-1 with cyanogen bromide, and sequenced completely. We also obtained a minor fragment, the 20 kDa fragment, in addition to the three characteristic fragments. Amino acid compositions of the cyanogen bromide peptides of the 20 kDa fragment indicated that a portion of S-1 heavy chains had lost their COOH-terminal 21 residues during limited tryptic digestion. Methylated amino acid residues were found at four positions: epsilon-N-monomethyllysine at position 32, epsilon-N-trimethyllysine residues at 127 and 549, and 3-N-methylhistidine at 754.     

Two-nucleotide codon change in a hemoglobin polymorphism of the Celebes black ape (Macaca nigra)

A hemoglobin polymorphism involving variant beta-chains was demonstrated in the Celebes black ape, Macaca nigra. Fingerprinting and amino acid analysis of the tryptic peptides from the two chain types have shown that they differ by a single amino acid substitution, between lysine and aspartic acid, which requires a two-nucleotide change in the corresponding codon. Another substitution in the same codon is found as a species between the black ape and that of other macaques.     

Mapping of phosphorylation sites of gel-isolated proteins by nanoelectrospray tandem mass spectrometry: potentials and limitations

Precursor ion scans have proven to be extremely useful for the characterization of unseparated peptide mixtures. In conjunction with the nanoelectrospray source, precursor ion scans provide a sensitive tool for the detection of posttranslationally modified peptides and have been used to determine phosphorylation sites of proteins digested in solution. In this report, we extend our previous work to the determination of protein phosphorylation sites of gel-isolated proteins. The in-gel digestion procedure developed in our laboratory for protein microsequencing was found to be suitable for phosphorylation mapping as well. The risk of losing hydrophilic peptides in the desalting step was decreased by using column packing material designed for the purification of oligonucleotides and by adjusting the pH conditions to the needs of phosphopeptide analysis. With this method, the tryptic phosphopeptides of beta-casein were detected after in-gel digestion at a sensitivity of 250 fmol of protein applied to the gel. The phosphorylation sites of two other proteins, Src-delta U and Op18, have similarly been mapped. Subpicomole to low-picomole amounts of protein starting material are needed in general, although we and others have reported attomole sensitivity for the detection of model phosphopeptides using precursor ion scans. This indicates that the success in determining phosphorylation sites depends crucially on the digestion, extraction, and detection efficiency for individual phosphopeptides.     

Structural characterization of synthetic model peptides of the DNA-binding cI434 repressor by electrospray ionization and fast atom bombardment mass spectrometry

The structural characterization of two synthetic model peptides of the cI434 repressor is described. Unequivocal determination of the structure was achieved by means of electrospray ionization mass spectrometry of the intact peptides and by fast atom bombardment mass spectrometric identification of complementary peptide fragments obtained by tryptic and chymotrypic digestion and partial separation by reversed-phase high-performance liquid chromatography. The results show the potential of this approach for characterizing synthetic peptides of relatively high molecular weight.     

Solution structure and peptide binding of the SH3 domain from human Fyn

BACKGROUND: The Src family of tyrosine kinases is involved in the propagation of intracellular signals from many transmembrane receptors. Each member of the family contains two domains that regulate interactions with other molecules, one of which is the Src homology 3 (SH3) domain. Although structures have previously been determined for SH3 domains, and ideas about peptide-binding modes have been proposed, their physiological role is still unclear. RESULTS: We have determined the solution structure of the SH3 domain from the Src family tyrosine kinase Fyn in two forms: unbound and complexed with a peptide corresponding to a putative ligand sequence from phosphatidylinositol 3' kinase. Fyn SH3 shows the typical SH3 topology of two perpendicular three-stranded beta sheets and a single turn of 3(10) helix. The interaction of SH3 with three potential ligand peptides was investigated, demonstrating that they all bind to the same site on the molecule. A previous model for ligand binding to SH3 domains predicts binding in one of two orientations (class I or II), each characterized by a consensus sequence. The ligand with the closest match to the class I consensus sequence bound with highest affinity and in the predicted orientation. CONCLUSIONS: The Fyn SH3 domain has a well-defined structure in solution. The relative binding affinities of the three ligand peptides and their orientation within the Fyn SH3 complex were consistent with recently proposed models for the binding of 'consensus' polyproline sequences. Although the affinities of consensus and non-consensus peptides are different, the degree of difference is not very large, suggesting that SH3 domains bind to polyproline peptides in a promiscuous manner.     

Structural analysis and quantitative evaluation of the modifications produced in human hemoglobin by methyl bromide using mass spectrometry and Edman degradation

The present study reports a procedure developed for the identification and quantitative analysis of the adducts formed by interaction of methyl bromide with human hemoglobin, based on combined analysis by electrospray mass spectrometry and automated Edman degradation of either intact globin chains or tryptic peptides of globin chains. The procedure has allowed identification of the reactive sites in human hemoglobin, and has been applied to the analysis of samples modified in vitro by methyl bromide. The results obtained represent the basis for the complete structural characterization of the modified hemoglobin and demonstrate the usefulness of the proposed analytical approach for the evaluation of the degree of alkylation and the identification of modified amino acids in proteins.     

Uptake and metabolism of serotonin by rat adrenal tissue in vitro

After incubation of separate zones of rat adrenals with radioactively labelled serotonin--at concentrations at which the amine had been previously shown to stimulate aldosterone biosynthesis--the tissue radioactivity was several times higher in the capsular ("zona glomerulosa") than in the decapsulated portions of the glands. High doses of unlabelled serotonin diminished the accumulation of radioactivity, but only when added simultaneously with the tracer. In the course of the incubation, radioactive 5-hydroxy-3-indoleacetic acid, i.e. the deaminated metabolite of serotonin, rapidly appeared in the medium. Most of the radioactive material accumulated by the adrenal was recovered in the cytosol fraction and was no longer identical with serotonin, but consisted mainly of 5-hydroxy-3-indoleacetic acid and another, unidentified metabolite. Unaltered serotonin was found in capsular adrenal tissue extracts only when a monoamine oxidase inhibitor (nialamide) has been added to the incubation medium. Rapid uptake and metabolism thus appeared to be the predominant features of the interaction of incubated adrenal tissue with serotonin. These events may have obscured the possible binding of very small amounts of serotonin to receptor sites. The observed accumulation of radioactivity in adrenal tissue was mainly due to delayed outflow of intracellulary formed metabolite, since 5-hydroxy-3indoleacetic acid was neither taken up by incubated adreanls nor bound by adrenal cytosol. No evidence of serotonin storage in the zona glomerulosa was found in these studies.