Sequence determination of eglin C using combined microtechniques of amino acid analysis, peptide isolation, and automatic Edman degradation

The complete amino acid sequence of a proteinase inhibitor, eglin c (Mr 8100), has been determined with less than 150 micrograms of the protein using the following microtechniques: (a) amino acid analysis with a low-nanogram amount of protein hydrolysate using dimethylaminoazobenzene sulfonyl chloride, (b) peptide isolation at the picomole level using the dimethylaminoazobenzene isothiocyanate (DABITC) precolumn derivatization method, and (c) automatic Edman degradation. One amino acid residue has been corrected for the previously reported sequence. The Contribution of each technique to the microsequencing is discussed. In addition, a new high-performance liquid chromatography system that gives a complete baseline separation of all phenylthiohydantoin-amino acids is described.

A new method for the selective isolation of cysteine-containing peptides. Specific labelling of the thiol group with a hydrophobic chromophore

A new method for the selective isolation of cysteine-containing peptides was designed. The method is based on the specific labelling of thiol groups with a hydrophobic chromophore followed by enzymic fragmentation of the labelled protein and reversed-phase high-pressure liquid-chromatographic separation of the peptide mixture. This new method has several distinct advantages: (1) the hydrophobic-chromophore-labelled cysteine-containing peptides are easily separated from non-cysteine-containing peptides by reversed-phase high-pressure liquid chromatography; (2) only cysteine-containing peptides are detected in the visible region with sensitivity at the low picomole level; this high sensitivity allows isolation of nanogram amounts of pure cysteine-containing peptide; (3) during sequence determination of the chromophore-labelled cysteine-containing peptides, the cysteine residues are released as coloured anilinothiazolinone derivatives and can be detected directly in the picomole range; (4) with proteins bearing several disulphide groups, each disulphide group may undergo a different degree of reduction, and therefore the recovery of individual cysteine-containing peptides may be used to deduce the disulphide linkages present in the native protein. Two thiol-specific reagents, 4-dimethylaminoazobenzene-4'-iodoacetamide and 4-dimethylaminoazobenzene-4'-N-maleimide, were synthesized and characterized. The method was successfully used to isolate five cysteine-containing peptides from a completely reduced monoclonal-antibody kappa-light chain raised against the azobenzenearsonate determinant and six cysteine-containing peptides from a kappa-light chain raised against streptococcal group A polysaccharide. The principle of this method is applicable to the isolation of any peptide containing amino acid residues that can be specifically labelled with a hydrophobic chromophore.

The complete amino acid sequence of the light chain variable region of two monoclonal anti-p-azobenzene-arsonate antibodies bearing the cross-reactive idiotype

Two monoclonal anti-p-azobenzene-arsonate antibodies produced by cell fusion of A/J spleen lymphocytes were selected. It had previously been shown that they both expressed the cross-reactive idiotype (CRI) and that the amino terminal sequence of their heavy chain variable region differed by only one amino acid substitution within the first 55 residues, at residue 41 in the second framework region. A novel, sensitive peptide-mapping method had indicated that the light chain of these two antibodies differed by at least three amino acid substitutions. Here, the complete amino acid sequence of the light chain variable region is presented. There are only 3 amino acid substitutions between the two antibodies, located in the first and second complementarity determining regions and the third framework region respectively. Although the variable region of the light chains of these two monoclonal antibodies show such a high degree of homology they differ by 26 and 27 substitutions from the reference sequence of the light chain of CRI+ anti-ABA serum antibodies. In addition, they are homologous to 4 other such CRI+ monoclonal antibody light chain sequences published so far, in which only 2 of the above 3 substitutions are not represented. The contribution of the light chain to the CRI is discussed.

Heterogeneity of cross-reactive idiotypes. Serological and structural analysis of monoclonal anti-p-azobenzene-arsonate antibodies expressing major and minor idiotypes

Hybridoma-derived monoclonal anti-p-azobenzene-arsonate (ABA) antibodies were obtained from fusions of ABA-KLH primed A/J spleen cells with three different myeloma cell lines. Of the 156 antibody secreting hybridomas 24% carried the cross-reactive idiotype (CRI), which is known to be shared by 20-70% of anti-ABA serum antibodies in A/J mice. The isotypes, SDS-PAGE patterns and the partial amino acid sequences of the V-regions of one CRI negative and six CRI positive hybridoma proteins were determined. These antibodies were IgGl, kappa and IgG2b, kappa. Some idiotype carrying monoclonal antibodies appeared to be serologically identical. Although the partial VH amino acid sequences of these monoclonal antibodies showed great homology with each other and with serum antibody, several sequence variations in framework residues as well as in the first and second complementarily determining regions (CDRs) were found. The cross-reactive idiotype of the anti-ABA antibodies, therefore, exhibits structural microheterogeneity, i.e. it consists of a family of non-identical but closely related molecules as previously reported (Alkan et al., 1980; Estess et al., 1980; Marshak-Rothstein et al. 1980). Here the N-terminal sequence of the VH regions from 14 CRI+ and 8 CRI- antibodies as well as the VL regions from 11 CRI+ and 8 CRI- monoclonal antibodies are compared. Analysis of the available data demonstrated that there are pairs of hybridoma proteins (both CRI+ and CRI-) which have identical sequences for VH or VL. This suggests that there exist a minimum of 4 germ line genes coding for CRI+ VH, CRI+ VL, CRI- VH and CRI- VL respectively. In addition, CRI+ VL has always been found in association with a CRI+ VH.

Sphingosine determination at the picomole level using dimethylaminoazobenzene sulphonyl chloride

A sensitive method (lower detection limit 5 picomoles) is proposed for the determination of sphingoid bases liberated from mammalian glycosphingolipids by acid hydrolysis. The azo dye 4-dimethylaminoazobenzene-4'-sulfonyl chloride reacts with the primary amino group of the sphingosine bases, forming a stable derivative. Excess reagent, which is degraded during the derivatization, and free amino sugars as common hydrolysis products of glycosphingolipids are completely separated by reversed-phase high-performance liquid chromatography. This method was applied to the determination of the glycosphingolipid content of mouse spleen and thymus.

A sensitive peptide mapping method. Identification of three amino acid substitutions within two anti-azobenzenearsonate monoclonal antibody light chains

Peptide mixtures, precolumn-derivatized with dimethylaminoazobenzene isothiocyanate, have been separated by reversed-phase high-performance liquid chromatography to generate a dimethylaminoazobenzene thiocarbamoyl peptide map. The eluted peptide derivatives are detected in the visible region with a sensitivity of 2-5 pmol and can be collected for direct structural analysis. This technique was applied to compare the sequence homology of two immunoglobulin light chains which were derived from two anti-azobenzenearsonate monclonal antibodies, namely 10K44-7A1 and 10K26-12A1. The complete variable region sequences of 10K44-7A1 and 10K26-12A1 light chains were established based on the sequence analysis of tryptic peptides, intact light chains and reference sequences obtained previously [Siegelman M. and Capra, J.D. (1981) Proc. Natl Acad. Sci. USA, 78, 7679-7683]. Altogether, three amino acid substitutions have been detected within complementary determining regions 1 and 2, and framework region 3, all requiring only a single base change at the DNA level. This new technique provides detection limits and the feasibility of analysing peptides which are not obtainable with conventional techniques.

Murine VK25 isotype sequence: monoclonal antibody 2S1.3 specific for the group A streptococcal polysaccharide

Antibodies 2S1.3 and 2S1.1 are hybridoma derived gamma 3K murine immunoglobulins with specificity for N-acetylglucosamine beta 1 leads to 3-linked to L-rhamnose, the immunodeterminant of the streptococcal group A polysaccharide. The VL 2S1.3 amino acid sequence is the second complete one reported with this specificity, and it is the first fully determined VK25 structure. The VK regions of this and the previously described monoclonal anti-A-CHO antibody 7S34.1 are compared with 17 selected partial and complete murine VK regions, preferentially from anti-polysaccharide antibodies. Both VK 2S1.3 and 7S34.1 increase the variability of existing murine VK regions; however, they are, as anti-A-CHO antibodies, most homologous to each other sharing the so far unique residue argine 74. The amino acid sequence of the constant region of 2S1.3 light chain was also determined. It was found to be identical with that of MOPC21, but different from MOPC41 and MOPC70 in residue positions 127, 129, 163 and 166.

A complete separation of dimethylaminoazobenzenesulphonyl-amino acids. Amino acid analysis with low nanogram amounts of polypeptide with dimethylaminoazobenzenesulphonyl chloride

A chromatographical system has been developed to give a complete baseline separation of all dimethylaminoazobenzenesulphonyl (DABS)-amino acids for high-sensitivity amino acid analysis [Chang, Knecht & Braun (1981) Biochem. J. 199, 547--556]. The system, which uses a Merck RP-18 column with phosphate buffer (12 mM, pH 6.5)/acetonitrile mixture, allows reliable analysis of DABS-amino acids at the 1--2 pmol level. The accuracy of this new system is demonstrated by the composition analysis of two immunoglobulin light chains (214 amino acid residues) with differences at only three amino acid residue positions.

Estimation of the local statistical noise in emission computed tomography

A simple modification of the filtered backprojection algorithm is presented for the computation of the local statistical noise in emission computed tomography. The technique is general in that any distribution of radioactivity may be accommodated. When applied to positron emission tomography, it is shown that the effects of photon absorption, random coincidences, radioactive decay, and detector nonuniformity may be included. Calculations have shown the effects of resolution, object size, and photon absorption on the statistical noise of disk-shaped emitters. Comparison of calculation and experiment show close agreement both in magnitude and spatial variation. Measurements of the noise level in tomograms of the brain obtained during continuous inhalation of 150-CO2 demonstrate that estimates of radioactivity concentration with a precision of a few percent are readily attainable.

N-terminal sequence analysis of polypeptide at the picomole level

This paper describes a manual method for N-terminal sequence analysis of polypeptides at subnanomole sensitivity. The polypeptide is degraded stepwise by using the dimethylaminoazobenzene isothiocyanate/phenyl isothiocyanate double-coupling method, and the released dimethylaminoazobenzenethiohydantoins of amino acids were identified by reversed-phase high-pressure liquid chromatography. The dimethylaminoazobenzenethiohydantoins are coloured compounds and can be detected in the visible region with the sensitivity limit of 1 pmol (signal-to-baseline noise ratio 5). A high-pressure liquid-chromatographic method was developed for complete analysis of all amino acid dimethylaminoazobenzenethiohydantoin derivatives, including the by-products of serine and threonine. Thus, without use of an automatic sequenator or radioactive materials, it is possible to determine the complete sequence of peptides and N-terminal sequence of proteins with less than 1 nmol of material.

Amino acid analysis at the picomole level. Application to the C-terminal sequence analysis of polypeptides

Amino acids labelled with dimethylaminoazobenzenesulphonyl chloride can be separated by reversed-phase high-pressure liquid chromatography and detected in the visible region (436 nm). All 19 naturally occurring amino acids can be separated on a Zorbax ODS column by employing two different gradient systems consisting of an acetonitrile/aqueous buffer mixture. As little as 2--5 pmol of an individual dimethylaminoazobenzenesulphonyl-amino acid can be quantitatively analysed with reliability, and only 10--30 ng of the dimethylaminoazobenzenesulphonylated protein hydrolysate is needed for each complete amino acid analysis. This new technique is as sensitive as any of the current amino acid analysis methods involving ion-exchange separation plus fluorescence detection, and is technically much simpler. By the combination of this sensitive amino acid-analysing technique with carboxypeptidase, we have been able to determine the C-terminal sequence of polypeptides at the picomole level.

Isolation and characterization of polypeptide at the picomole level. Pre-column formation of peptide derivatives with dimethylaminoazobenzene isothiocyanate

Polypeptides coupled with dimethylaminoazobenzene isothiocyanate through their amino groups to form dimethylaminoazobenzenethiocarbamoyl- (DABTC-)peptides can be separated by reversed-phase high-pressure liquid chromatography and detected in the visible region (436 nm). As little as 1 ng (2 pmol) of a DABTC-pentapeptide can be identified against a stable base-line with the signal-to-noise ratio of 10. The DABTC-peptides can also be recovered from the column, and their N-terminal amino acids (obtained by direct treatment with aqueous acid) and amino acid compositions and sequences can be all analysed at the picomole level. The power of this method is demonstrated by the complete separation and characterization of model peptides, peptide hormones and peptides derived from enzymic fragmentation of proteins. This new technique should provide a sensitive and efficient tool for peptide analysis at the nanogram level.

Immunochemistry of human plasma apolipoprotein C-II as studied by radioimmunoassay

The immunoreactivity of human plasma apolipoprotein C-II was investigated using a specific radioimmunoassay. In whole plasma, the mean value quantitated was 2.21 +/- 0.415 mg/dl, while in delipidated plasma, a mean value of 3.84 +/- 1.186 mg/dl was obtained, suggesting that the antigenic sites of the apolipoprotein were not fully detected in unmodified plasma by our antibody preparation. Two detergents, Tween-20 and Triton X-100, were studied to determine if they could enhance the immunoreactivity of apolipoprotein C-II in whole plasma. At concentrations of 0.012-0.06%, Tween-20 markedly increased the immunoreactivity of whole plasma, but not of delipidated plasma, indicating that antigenic sites of plasma apolipoprotein C-II has been exposed by Tween-20. In contrast, Triton X-100 had no effect on the immunoreactivity of whole plasma apolipoprotein C-II. A radioimmunoassay conducted in the presence of 0.06% Tween-20, resulted in a mean value in whole plasma (3.39 +/- 1.11 mg/dl) that was not significantly different from that obtained when the assay was done on delipidated samples. The immunoreactivity of VLDL apolipoprotein C-II was also drastically enhanced following lipolysis by bovine milk lipoprotein lipase, supporting the hypothesis that antigenic sites are masked by the lipids. Finally, the mechanism responsible for the effect of Tween-20 on apolipoprotein C-II immunoreactivity was investigated. The results obtained from circular dichroism and ultracentrifugation suggest that the detergent may dissociate the apolipoprotein from lipoprotein particles, thus fully exposing the antigenic sites for reaction with antibodies.

Manual solid phase sequence analysis of polypeptides using 4-N-N,-dimethylaminoazobenzene 4'-isothiocyanate

A manual solid-phase method for sequence analysis of polypeptides is described. The immobilized polypeptide was subjected to stepwise degradation by Edman-type reagent, using the 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate phenyllisothiocyanate double coupling method. The N-terminal amino acids were released (after conversion reaction) as 4-N,N-dimethylaminoazobenzene 4'-thiohydantoin (identified by thin layer chromatography) and phenylthiohydantoin derivatives. The method required 2--10 nmol polypeptide.

The destruction of serine and threonine thiohydantoins during the sequence determination of peptides by 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate

1. A mechanism for the destruction of serine and threonine thiohydantoins during protein sequence analysis by the Edman-type degradation is proposed. The mechanism begins with the dehydration of serine and threonine side chains (at the cyclization stage) which occurs mainly in anhydrous acid solution. The dehydrated derivatives finally polymerize by way of the reactive methylene group (enamine) to form polymers with various molecular weights. In aqueous acid solution, the dehydrated thiohydantoins of serine and threonine undergo hydration (according to the Markovnikov rule) and ring fission, which leads to the irreversible breakdown of thiohydantoin ring. The serine derivative shows a much greater tendency to undergo these side-reactions than the threonine derivative. 2. In the presence of oxygen, the alkaline hydrolysis of amino acid thiohydantoins goes through an oxidation-deamination reaction at the C-N bond of the thiohydantoin ring and leads to the formation of thiourea derivative and keto acids. This reaction mechanism accounts for the low recoveries of amino acid obtained from the alkaline hydrolysis of amino acid thiohydantoins.

High-sensitivity sequence analysis of peptides and proteins by 4-NN-dimethylaminoazobenzene 4'-isothiocyanate

A manual high-sensitivity sequencing method is described, in which 4-NN-dimethylaminoazobenzene 4'-isothiocyanate is used for the stepwise degradation of amino acid residues from the peptides. The 4-NN-dimethylaminoazobenzene 4'-thiazolinones of amino acids that were released, after conversion into their thiohydantoin derivatives, were identified by t.l.c. on polyamide sheets. This new method is simple and sensitive, and requires only 2-10nmol of peptides or proteins for extended sequence analysis. The method was tested on the sequence analysis of a hexapeptide (Leu-Trp-Met-Arg-Phe-Ala), bradykinin, glucagon and native lysozyme. Results show that the proposed procedure is a sensitive method for the sequence determination of short peptides as well as for the partial sequence determination of intact proteins.

Improved chromatographic identification of coloured amino acid thiohydantoins

A new N-terminal reagent for peptides and proteins, 4-N,N-dimethylamino-naphthylazobenzene-4'-isothiocyanate, is described which gives purple thiohydantoin derivatives; chromatographic separation of 24 amino acid thiohydantoins is reported. Such standard purple derivatives can be used as markers in the separation of the red 4-N,N-dimethylaminoazobenzene-4'-thiohydantoins. Conversely, standard red thiohydantoins can be used as markers in the separation of unknown purple amino acid thiohydantoins. In two-dimensional thin-layer chromatography, the precision of identifying the unknowns can be greatly improved by running markers with a colour different from the unknowns on the same side of the sheet.

A novel manual method for protein-sequence analysis

A novel manual method for protein-sequence analysis is described. Three peptides, the hexapeptide (Leu-TRP-Met-Arg-Phe-Ala), insulin A chain and glucagon were used to test this technique. Peptides (1 or 2 nmol) were hydrolysed with acid and their qualitative amino acid compositions were confirmed by reacting with 4-NN-dimethylaminoazobenzene-4'-sulphonylchloride and 4-NN-dimethylaminoazobenzene 4'-isothiocyanate. Sequence determination of 20-200 nmol of peptide was then performed by the combined use of phenyl isothiocyanate and 4-NN-dimethylaminoazobenzene 4'-isothiocyanate, a new procedure that is analogous to the dansyl-Edman method with the replacement of dansyl chloride by 4-NN-dimethylaminoazobenzene 4'-isothiocyanate as the N-terminal residue determination reagent. On t.l.c. this new N-terminal reagent gave brightly coloured 4-NN-dimethylaminoazobenzene-4-thiohydantoins of amino acids and showed the following advantages: (1) the detection sensitivity is in the pmol range; (2) u.v. observation is not required; (3) there is no destruction of acid-labile amino acids; (4) two-dimensional t.l.c. separation is adequate to identify 24 amino acids, except leucine and isoleucine (this pair of amino acids can be resolved by using 4-NN-dimethylaminoazobenzene-4'-sulphonyl chloride); (5) the determination of a new N-terminal residue (from coupling to t.l.c. identification) takes only 3 h; (6) the colour difference beteen isothiocyanate, thiocarbamoyl and thiohydantoin derivatives facilitates the identifications.

4-NN-dimethylaminoazobenzene 4'-isothiocyanate, a new chromophoric reagent for protein sequence analysis

4-NN-Dimethylaminoazobenzene 4'-isothiocyanate was synthesized for the purpose of improving the ease and sensitivity of peptide sequence analysis. The method of 4-NN-dimethylaminoazobenzene 4'-isothiocyanate synthesis, the preparation of 24 4-NN-dimethylaminoazobenzene-4'-thiohydantoins of amino acids and their t.l.c. separation are described. All the thiohydantoins, except those of leucine and isoleucine, could be satisfactorily separated by chromatography on a two-dimensional polyamide sheet. The sensitive azo group permits the detection of 4-NN-dimethylaminoazobenzene-4'-thiohydantoins of amino acids as red spots down to pmol amounts directly on the sheet. A simple sensitive method for sequencing dipeptides and the first two or three N-terminal amino acids of proteins is also reported. The colour change of the spots from purple to blue to red after being exposed to HCl vapour, corresponding to the chemical change from 4-NN-dimethylaminoazobenzene-4' isothiocyanate to the 4-NN-dimethylaminoazobenzene-4'-thiocarbamoyl amino acid derivative to the 4-NN-dimethylaminoazobenzene-4'-thiohydantoin amino acid derivative, reveals a very interesting and valuable feature of this reagent.

Amino acid sequence of flagellin of Bacillus subtilis 168. I. Cyanogen bromide peptides

Sequence studies are presented on the cyanogen bromide peptides derived from the flagellin of Bacillus subtilis 168. Eight unique CNBr peptides, ranging in length from 4 to 113 residues, were isolated in pure state. These peptides accounted for the amino acid composition of flagellin. The NH2-terminal methionyl residue of the protein reacted only partially with CNBr. Partial cleavage was observed at a Met-Glu bond (residues 22 to 23) of the protein.

Amino acid sequence of flagellin of Bacillus subtilis 168. III. Tryptic peptides, N-bromosuccinimide peptides, and the complete amino acid sequence

Of the 28 expected tryptic peptides from Bacillus subtilis 168 flagellin, 24 were isolated and sequenced. Several overlapping tryptic peptides were also characterized. Studies were also performed on two peptides of 142 and 162 residues isolated after cleavage of the flagellin molecule at the single tyrosine residue (residue 142) with N-bromosuccinimide. These studies together with the previous data on the cyanogen bromide peptides and the tryptic peptides from maleylated flagellin permitted the complete amino acid sequence to be established: (see article). The primary structure reveals no obvious regularities or major repetitions of homologous sequences. Hydrophobic residues are distributed randomly in the amino acid sequence. However, the distribution of charged residues is strikingly asymmetric. The NH2-terminal region (residues 1 to 101) possesses a net charge of 6 plus, the middle of the molecule (residues 102 to 203), a net charge of 9 minus, and the COOH terminal region (residues 204 to 304), a net charge of 4 minus.

On the amino-acid sequence of flagellin from Bacillus subtilis 168: comparison with other bacterial flagellins

A partial amino-acid sequence of Bacillus subtilis 168 flagellin is presented. The region of unassigned sequence in this 304-residue polypeptide chain spans residues 158-173. Comparison of the 27-residue aminoterminal CNBr peptide of B. subtilis 168 flagellin with that derived from the flagellin of the serologically unrelated strain of B. subtilis, W23, shows only three conservative substitutions, whereas the 16-residue carboxyl-terminal peptides derived from these flagellins were identical. The comparison of the very limited sequence information available on the flagellins of Salmonella and Proteus with that on B. subtilis indicates homology between these proteins.