Preparation and partial structural characterization of alpha1T-glycoprotein from normal human plasma

alpha1T-glycoprotein (alpha1T) was isolated from normal human plasma in the immunochemically homogeneous state. The partial amino acid sequence and carbohydrate chains of this glycoprotein were determined. To achieve this, the carboxymethylated alpha1T was analyzed by sequencing some of the lysylendoprotease, V8 protease, tryptic, and cyanogen bromide peptides as well as the N-terminal sequence of the protein. A large number of amino acid residues (460 amino acids) was determined by chemical procedure. The peptide sequences were compared with that of other proteins. A high degree of homology was found for proteins of the albumin family. Further, human alpha-albumin, a new member of this protein family, showed an amino acid sequence identical to that of alpha1T indicating that these two proteins are very similar in amino acid sequence and composition. These proteins are closely related to alpha-fetoprotein; however, five carbohydrate chains were found on alpha1T at Asn12, Asn88, Asn362, Asn381, and Asn467 as biantennary complex type chains and the chain on Asn362 possessed a rare consensus sequence of Asn-X-Cys. Thus, alpha1T distinguishes itself by possessing five N-glycans, a finding reported here for the first time for the ALB family.

Determination of the molecular structure of the human free secretory component

Here, we present the experimental data, leading to determination of the primary structure, the linkage of the carbohydrates and the arrangements of the disulfide bonds of the human free secretory component. Methods of protein chemistry were used. The protein can be divided into five homology regions and is a member of the immunoglobulin superfamily.

Structure and conformational analysis of lipid-associating peptides of apolipoprotein B-100 produced by trypsinolysis

Apolipoprotein B-100 (apo B-100) contains putative lipid-associating regions that are, in part, responsible for its overall structure in human plasma low-density lipoproteins. Some of these regions have been identified by reassembly of the total tryptic peptides of apo B-100 with bovine brain sphingomyelin, 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and dimyristoylphosphatidylcholine (DPMC). Although more than 500 tryptic peptides are predicted from the known number of arginines and lysines in apo B-100, significant amounts of only 13 peptides spontaneously associate with all three phospholipids. These peptides share some structural characteristics, as predicted by several algorithms, that distinguish them from the water-soluble apolipoproteins. Most apolipoproteins associate with lipids via amphipathic helices and are highly helical in native and reassembled lipoproteins. Analysis of all apo B-100 lipophilic peptides by circular dichroism and by use of a predictive algorithm reveals no evidence of amphipathic helices. Although the predictive algorithm suggested that the lipophilic peptides of apo B-100 contain the sequence determinants for beta-sheet, no spectroscopic evidence for this structure was found. We conclude that the lipophilic regions of apo B-100 liberated by trypsinolysis are highly hydrophobic, although their secondary structures do not fit any simple model.

The primary structure of human apolipoprotein A-IV

Human apolipoprotein (apo) A-IV was purified from chylous ascites fluid. Proteolytic peptides produced by trypsin and Staphylococcus aureus V8 proteinase digestions were purified by high-performance liquid chromatography and sequenced. Human apoA-IV contains 376 amino acid residues. The peptide-derived sequence generally matches two previously reported DNA-derived amino acid sequences except for discrepancies in five positions. In order to examine these discrepancies further, one complete apoA-IV cDNA clone and another partial clone were sequenced. Comparison of all the available information indicates that the peptide-derived sequence reported here is accurate. Sequencing errors probably account for some of the discrepancies between the two primary sequences predicted by earlier nucleotide analyses. In certain positions, however, bona fide sequence heterogeneity or cloning artifact cannot be excluded.

Analysis of 4-N,N-dimethylaminoazobenzene 4'-thiohydantoin amino acids at sub-picomole levels by high-performance liquid chromatography: simultaneous manual sequencing of picomole quantities of several polypeptides

A single-column high-performance liquid chromatographic separation of 4-N,N-dimethylaminoazobenzene 4'-thiohydantoin amino acid derivatives, generated during polypeptide sequence analysis by the 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate/phenylisothiocyanate double coupling technique, is described. Recovery of the serine and threonine derivatives was improved by substituting boron trifluoride-diethyl etherate for trifluoroacetic acid in the thiazolinone cleavage reactions. Residues, including the S-carboxymethyl derivative of cysteine, were assigned after a single injection and a cycle time of 30 min. Quantities of 4-N,N-dimethylaminoazobenzene 4'-thiohydantoin amino acid derivatives as low as 100 fmol were detected. Interference of sequencing artefacts with residue assignment was avoided. This technique allows simultaneous manual sequencing of several proteins or peptides at the level of a few picomoles.

The complete amino acid sequence of proapolipoprotein A-I of chicken high density lipoproteins

The complete amino acid sequence of proapolipoprotein (proapo) A-I of chicken high density lipoproteins was determined by sequencing overlapping peptides produced by trypsin, S. aureus V8 protease, and cyanogen bromide cleavage. There are 240 amino acid residues in mature chicken apoA-I. By direct sequence analysis of a cyanogen bromide peptide, we also determined the sequence of a 6-amino-acid prosegment which is present at approx. 10% the molar amount of the mature peptide in chicken plasma. Sequence comparison among apoA-I from chicken, human, rabbit, dog and rat, and secondary structure analysis indicate that while the degree of sequence homology is only moderate (less than 50% between chicken and man), there is good conservation of apoA-I secondary structure, especially in the N-terminal two-thirds of the protein in these widely separated species.

Hybrid glycophorins from human erythrocyte membranes. I. Isolation and complete structural analysis of the hybrid sialoglycoprotein from Dantu-positive red cells of the N.E. variety

The hybrid glycophorin in Dantu-positive human erythrocytes of the N.E. variety was not cleaved by treatment of intact cells with various proteases, in contrast to normal glycophorins. Therefore, it could be purified by phenol/saline extraction of membranes from trypsin-treated and chymotrypsin-treated red cells and subsequent gel filtration in the presence of Ammonyx-LO. The complete structure of the hybrid molecule, comprising 99 amino acid residues, was elucidated by sequence analyses of peptides prepared by chymotrypsin, trypsin, cyanogen bromide or V8 proteinase treatment. The N-terminal 39 residues and the glycosylation of the molecule were found to be indistinguishable from those of blood-group-s-specific glycophorin B. Conversely, the residues 39-99 were shown to be identical with the residues 71-131 of the major blood-group M-active or N-active sialoglycoprotein (glycophorin A). Hemagglutination inhibition assays revealed that the Dantu antigen represents a labile structure. The receptor might be located within the residues approximately 28-40 of the hybrid glycophorin, as judged from the effects of modifications of membranes. Our data provide an explanation for the previous findings that Dantu-positive cells (N.E. type) exhibit a protease-resistant N antigen and a qualitatively altered s antigen.

Complete amino-acid sequence of the natural ATPase inhibitor from the mitochondria of the yeast Candida utilis

The complete alignment of the 63 residues of the mitochondrial ATPase inhibitor from the yeast Candida utilis has been determined. The sequence study was carried out mainly by automatic (liquid and solid-phase) methods. Peptides were obtained by enzymatic digestion with clostripain and purified by reverse-phase high-performance liquid chromatography. The ATPase inhibitor contains three sets of repetitive sequences and eight clusters of charged residues, as also found in the inhibitor of Saccharomyces cerevisiae, with which it shares 58.7% homology of conserved residues. When the two yeast ATPase inhibitor sequences were compared to that of beef heart, 20 residues remained common to the three alignments, although the latter protein contained a long histidine-rich insertion, only found in this inhibitor. Most of the homologous residues were clustered near the center of the protein, which by partial proteolytic digestion of the beef heart ATPase inhibitor [Dianoux, A.C. et al. (1982) FEBS Lett. 140, 223-228] has already been shown to be involved in the biological function.

The primary structure of apolipoprotein A-I from rabbit high-density lipoprotein

The amino acid sequence of rabbit apolipoprotein A-I (apo A-I) has been determined by degradation and alignment of two overlapping sets of peptides obtained from tryptic and staphylococcal digestions. All of the peptides of rabbit apo A-I resulting from digestion by staphylococcal protease were isolated and sequenced except residues 33-37. A digestion with trypsin was employed to find overlapping and missing peptides. The N-terminus of rabbit apo A-I was confirmed by sequencing the intact protein up to 20 residues while the C-terminus was identified through its homology with human apo A-I. The protein contains 241 residues in its single chain. Its primary structure is highly homologous to the reported canine apo A-I (80%) and human apo A-I (78%), but exhibits less similarity with rat apo A-I (60%). Like human apo A-I, rabbit apo A-I contains very little histidine (2) and methionine (1); it does however have two residues of isoleucine. Based on a comparison of the hydrophobic-hydrophilic character of apo A-I residues with that of the two synthetic peptides that activated lecithin: cholesterol acyltransferase (Pownall et al. and Yokoyama et al.), we found that the five segments with the highest corresponding homologies on the protein are located within the N-terminal half. This suggests that the N-terminal half of apo A-I contains the major portion of regions activating lecithin: cholesterol acyltransferase.

High frequency antigens of human erythrocyte membrane sialoglycoproteins, III. Studies on the EnaFR, Wrb and Wra antigens

The nature of the common erythrocyte antigens EnaFR and Wrb, that are both absent from En(a-) cells, and the rare Wra receptor, apparently encoded by an allele of Wrb, was investigated. Various modification, fractionation or cleavage products of erythrocyte membranes were used in hemagglutination inhibition assays. The EnaFR and Wrb antigens were shown to represent labile structures within the residues approx. 62-72 of the major (MN) sialoglycoprotein that require lipids, at least for complete expression of antigenic activity. During the course of these experiments, the arrangement of the MN glycoprotein's peptide chain with respect to the lipid bi-layer was also studied, using various proteinases. Furthermore, the MN glycoprotein was found to aggregate with the major membrane protein (band 3) in the presence of Triton X-100. The Wra antigen was shown to exhibit properties that differ considerably from those of the Wrb receptor. Analyses on the MN glycoprotein, isolated from the red cells of the only known Wra homozygote and two WraWrb individuals, did not reveal any amino-acid exchange within the residues 40-96 of the molecule. Therefore, the Wr locus that determines the presence or absence of the Wrb antigen on the MN glycoprotein might influence the post-translational modification of amino-acid residues, the structure of tightly bound lipids or the aggregation of the MN glycoprotein with a different protein such as band 3.

Immunological studies on the beef heart natural ATPase inhibitor: localization of an antigenic determinant in the inhibitor molecule

Antibodies were raised against the beef heart mitochondrial ATPase inhibitor. This antiserum prevented the ability of the ATPase inhibitor to inhibit the F1 ATPase activity. Peptide fragments obtained by enzymatic cleavage of the inhibitor protein were tested by immunoblotting or ELISA for their response to the anti-inhibitor antiserum. An antigenic determinant was located in the sequence spanning His 48 to Lys 58 of the inhibitor molecule.

The amino acid sequence of a lambda light chain presenting abnormal physicochemical and antigenic features

The amino acid sequence of the light chain of a human monoclonal IgA1 (Mem) was established, in part by analogy with already known sequences. By homology its variable part was shown to belong to the V lambda I subgroup while the isotype-associated amino acid residues characterized it as Mcg+, Kern+ and Oz-. The normal primary structure of this chain was in contrast to its abnormal physical and antigenic properties: (a) its apparent molecular mass estimated by SDS/polyacrylamide gel electrophoresis, by gel filtration chromatography and by gradient ultracentrifugation was found to be lower by approximately equal to 10% than the values (23.5 kDa) of 'normal' light chain used as controls; (b) the lambda I chain Mem, when tested in native state was not antigenically reactive. These abnormalities were reverted when the chain was treated with 8 M urea. These data suggest that the abnormal behaviour of lambda I chain Mem is at a conformational level.

Identification of peptides containing tryptophan, tyrosine, and phenylalanine using photodiode-array spectrophotometry

The characteristic absorption spectra of aromatic amino acids between 240 and 310 nm were used to identify tryptophan, tyrosine, and phenylalanine-containing peptides. In acidic solution, the absorption spectra of these amino acids exhibit minima or maxima at 255, 270, and 286 nm. Based on these characteristics, the content of the aromatic amino acid in peptide can be estimated. For this study, 2 nmol of tryptic peptides from human apolipoprotein A-1 was separated by high-performance liquid chromatography using a reverse-phase column. The peptide fragments were monitored by a photodiode-array spectrophotometer. This new approach offers a rapid, simple, sensitive, and direct identification of peptides containing aromatic amino acids. Those containing Trp, which may be of interest for DNA sequencing and important in sequence analysis of proteins, can be selectively purified using this technique.

Inactivation of human high- and low-molecular-weight urokinases. Analysis of their active site

We previously demonstrated that 3,4-dihydro-3,4-dibromo-6-bromomethylcoumarin (dihydrocoumarin I) inhibited high-molecular-weight urokinase through a mechanism-based (suicide) inactivation (M. Reboud-Ravaux, G. Desvages and F. Chapeville (1982) FEBS Lett. 140, 58-62). In order to define the site of alkylation, peptic peptides were prepared from urokinase (heavy form) treated first by tritiated dihydrocoumarin I. After separation by reverse-phase HPLC, the labelled fragments were sequenced. His-46 in the B-chain of urokinase (heavy form) had been selectively alkylated, proving that this amino acid forms part of the active site. 3,4-Dihydro-3-benzyl-6-chloromethylcoumarin (dihydrocoumarin II) was more reactive than dihydrocoumarin I against urokinase (heavy form) by a factor of 130. Low-molecular-weight urokinase was inactivated by dihydrocoumarin II slightly more slowly than urokinase (heavy form), showing a decrease of 30% in the corresponding second-order rate constant. In contrast, dihydrocoumarin I displayed an analogous reactivity against light and heavy forms of urokinase. As expected, in the absence of the alkylating moiety, such as in 3,4-dihydro-3-benzylcoumarin (dihydrocoumarin III), no inactivation was observed. It is note-worthy that dihydrocoumarin II which carried an extra-aromatic group fitted well within the active site of light and heavy urokinases, suggesting a nonpolar character for their primary binding site.

Solid-phase protein and peptide sequencing using either 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate or phenylisothiocyanate

Automated solid-phase sequencing using 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate (DABITC) double coupling or regular phenylisothiocyanate (PITC) degradation procedures have been investigated. Employing sensitive high-performance liquid chromatography for the identification of amino acid thiohydantoin derivatives (PTH and DABTH), both methods were capable of sequencing immobilized peptides or proteins at the subnanomole levels. In the sequencing program using DABITC, alternate methanol and dichloroethane washes and automated conversion using methanolic HCl containing dithiothreitol were introduced to obtain clean thiazolinones and to ensure high recovery yields of the thiohydantoins. Using regular PITC degradation with a 59-min program, the background peaks of the side products could be reduced to enhance HPLC identification. Peptides or proteins attached to the glass beads or resins via the carboxyl terminii or epsilon-amino groups of lysyl residues could be readily sequenced up to 30 identifiable degradation cycles, where the sequencing is generally terminated due to the increased background components.

Primary structure of human class II histocompatibility antigens. Reversed-phase high-performance liquid chromatography for integral membrane proteins

The amino acid sequence of the human HLA-DR2 class II antigen was determined with the aid of high-performance liquid chromatography. By applying exclusively Hypersil-ODS as the stationary phase in combination with three buffer systems, the amino acid sequences of the extracellular parts of the DR alpha- and DR beta-chains could be established. Moreover, the sensitivity of the procedure allowed the determination of the primary structures of additional class II polypeptides isolated together with the DR2 alpha- and the DR2 beta-chains. Significant insight into the heterogeneity of class II molecules was thereby obtained. In addition, a simple, rapid and selective method of general applicability is described for the isolation of membrane fragments of integral membrane proteins. Using Sep-Pak cartridges with a mobile phase containing 60% formic acid and varying 1-propanol concentrations, the highly hydrophobic peptides can selectively be separated from the hydrophilic fragments.

Separation of dimethylaminoazobenzenethiohydantoin amino acids by high-performance liquid chromatography at low picomole concentrations

The separation of all common dimethylaminoazobenzenethiohydantoin (DABTH) amino acids derived from modified Edman sequencing can be achieved by using high-performance liquid chromatography. All derivatives, including DABTH-Ile and DABTH-Leu, can be readily separated in a solvent mixture of sodium acetate buffer and 1% ethylene dichloride in acetonitrile. The high absorbance of the DABTH amino acids at 436 nm makes possible the quantitative determination of these derivatives at picomole concentrations in a relatively short time (30-40 min).

Affinity labelling of the allosteric site of the L-lactate dehydrogenase of Lactobacillus casei

Kinetic investigations employing the substrate analogues 2-oxoglutarate and phospho(enol)pyruvate indicate that the allosteric L-lactate dehydrogenase (EC 1.1.1.27) of Lactobacillus casei has a non-catalytic pyruvate-binding site to which, in addition to pyruvate, the allosteric effector fructose 1,6-bisphosphate can also be found. A modification using the 14C-labelled substrate analogue 3-bromopyruvate induces a loss of regulation by fructose 1,6-bisphosphate. The histidine residue labelled by 3-bromopyruvate is homologous to histidine-188 which is part of the anion-binding site of the non-allosteric vertebrate L-lactate dehydrogenases. Thus, the allosteric site of the allosteric L-lactate dehydrogenases corresponds to the anion-binding site of the non-allosteric vertebrate enzymes.

The complete primary structure of the allosteric L-lactate dehydrogenase from Lactobacillus casei

The polypeptide chain of the allosteric L-lactate dehydrogenase (EC 1.1.1.27) of Lactobacillus casei consists of 325 amino acid residues. Despite the strikingly different enzymatic characteristics of the allosteric L-lactate dehydrogenase of L. casei and of the non-allosteric vertebrate enzymes, the sequence of the allosteric enzyme shows a distinct homology with that of the non-allosteric vertebrate enzymes (average identity: 37%). An especially high sequence homology can be identified within the active center (average identity: 70%). A clear deviation of the L. casei enzyme from the vertebrate enzyme is the lack of the first 12 amino acid residues at the N terminus and an additional 7 amino acid residues at the C terminus. The localization of the binding site of the allosteric effector D-fructose 1,6-bisphosphate and pH and effector-induced changes of the spectroscopic properties are discussed on the basis of the primary structure.

Complete amino acid sequences of two protease inhibitors in the venom of Bungarus fasciatus

Two analogous protease inhibitors, VIIIb and IX in the venom of Bungarus fasciatus were reduced and carboxymethylated. Tryptic peptides were separated by cellulose thin-layer peptide mapping technique, and amino acid sequences were analyzed by DABITC/PITC double coupling method. Alignment of all tryptic peptides was established by analyses of chymotryptic peptides and further confirmed by Staphylococcus aureus V8 protease digestion. IX consisted of 65 amino acid residues. VIIIb consisted of 62 residues, identical to the N-terminal 62-amino acid sequence of IX.

The primary structure of the constant part of mu-chain-disease protein BOT

The complete primary structure of the constant part of the mu-chain-disease protein, BOT, was established. It includes the whole CH2, CH3 and CH4 domains. two amino acid changes were found, at positions 309 (Ser leads to Gly) and 333 (Val leads to Gly) (GAL numbering). In two additional monoclonal mu chains (SCO and CO), the same positions showed an amino acid variability. From these data it may be concluded that four types of mu chains exist in the human: (1) GAL type with Ser-309 and Val-333; (2) OU type with Gly-309 and Val-333; (3) SCO type with Ser-309 and Gly-333; (4) BOT/CO type with Gly-309 and Gly-333. The meaning of this molecular polymorphism is discussed.