Structural characterization of a biologically active human lipocortin 1 expressed in Escherichia coli

Lipocortin or annexin 1 is a calcium-dependent phospholipid-binding protein which probably acts as a glucocorticoid- regulated anti-inflammatory factor. cDNA for human lipocortin 1 was cloned in the pT7.7 expression plasmid under the control of the inducible bacteriophage T7 RNA polymerase promoter. Upon induction with isopropyl thio-beta-D-galactoside, large amounts of the protein were produced and accumulated in Escherichia coli in a soluble form. The recombinant protein was purified to homogeneity by means of two subsequent ion-exchange chromatographic steps. The final yield was about 30 mg/l bacterial culture. Electrospray mass spectrometric analysis of the purified protein demonstrated that the recombinant product corresponds to the native human lipocortin 1, without the initial methionine and with a free N-terminal alanine; tryptic peptide mapping by fast-atom-bombardment mass spectrometry showed that the recombinant protein contains cysteine residues at positions 263 and 324 with free thiol groups, whereas Cys270 and Cys343 are probably involved in an intrachain disulfide bridge. Recombinant human lipocortin 1 reduces the carrageenin-induced paw oedema in rat in vivo and inhibits porcine pancreatic phospholipase A2 activity in vitro; in both cases, a dose-related response is observed.

Mass spectrometric analysis of the HMGY protein from Lewis lung carcinoma. Identification of phosphorylation sites

The primary structure of the Lewis lung carcinoma protein HMGY belonging to the nuclear group of proteins HMGI (high mobility group I) was determined using electrospray and fast atom bombardment mass spectrometry. It was demonstrated that the sequence of the tumor protein corresponds to the amino acid sequence derived from the cDNA from cultured cells and that the N-terminal serine residue is N-acetylated. Moreover, the two high performance liquid chromatography-purified forms Y1 and Y2 of the protein HMGY were shown to differ at the level of serine phosphorylation, since they contain three phosphate and two phosphate groups, respectively, in the C-terminal region. No other modification was detected in the remaining part of the molecule.

Study of interaction of styrene oxide with angiotensin by mass spectrometry

The present study describes how mass spectrometry was extensively applied to the characterization and quantification of modified amino acids within the polypeptide chain of Angiotensin I, chosen as model substrate, combining the use of fast atom bombardment mass spectrometry with gas chromatography--mass spectrometry. The reaction products after in vitro incubation of Angiotensin I with styrene oxide, a well known carcinogen, under different conditions, have been characterized: a prominent reactivity of several potential nucleophilic sites of Angiotensin I was shown, including two histidine residues and a tyrosine residue; it is worth noting that it has never been stated that tyrosine is highly reactive with styrene oxide. The results obtained demonstrate the usefulness of mass spectrometry for the structural determination of chemically modified amino acids in peptides and proteins, and the presence of a reliable relationship between reaction conditions and the production of alkylated amino acids. This characterization procedure offers the possibility of identifying reactive sites following exposure to unknown alkylating agents.

Characterization of Hemoglobin Lepore Variants by Advanced Mass-Spectrometric Procedures

We describe an analytical protocol for characterizing the molecular structure of hemoglobin (Hb) Lepore variants by using two different mass-spectrometric approaches. The first method consists of direct examination of the chromatographically separated hybrid globins by electro-spray mass spectrometry; the variant Lepore globin is identified through the accurate determination of its molecular mass. Alternatively, the anomalous globins are digested with trypsin and their structures are determined by fast atom bombardment mass-spectrometric analysis of the peptide mixture. The application of this procedure to the identification of Hb Lepore Boston and Hb Lepore Baltimore is described.

Characterization of hemoglobin lepore variants by advanced mass-spectrometric procedures

We describe an analytical protocol for characterizing the molecular structure of hemoglobin (Hb) Lepore variants by using two different mass-spectrometric approaches. The first method consists of direct examination of the chromatographically separated hybrid globins by electro-spray mass spectrometry; the variant Lepore globin is identified through the accurate determination of its molecular mass. Alternatively, the anomalous globins are digested with trypsin and their structures are determined by fast atom bombardment mass-spectrometric analysis of the peptide mixture. The application of this procedure to the identification of Hb Lepore Boston and Hb Lepore Baltimore is described.

Mass spectrometric methodologies for the analysis of biotechnologically produced protein pharmaceuticals

The biotechnological production of protein pharmaceuticals is: i) initially a research problem, to which Chemistry is essential; ii) second, a problem of "quality control". The concept of "quality control" in terms of biotechnological products is quite different from the control of traditional products as there is still no history of the safety of the long term effects of these products in man. The "quality control" of a biotechnological product refers both to the individual production process and to the product itself. The methods for "quality control" can very greatly for two different processes, even if they lead to the same product. The "quality control" of a biotechnological product is concerned above all with the following: i) development and characterization of the production of recombinant organism; ii) culture and fermentation control, including the control of all equipment and product used; iii) control of the recovery and purification processes; iv) structural control of the final product. Mass spectrometry, belonging widely to the chemical sciences, plays an important role in biotechnology because of its capability to set-up several fast, sensitive and specific analytical and structural methods, which are invaluable for the full characterization of proteins, representing the ultimate objective of genetic manipulation. This paper review some recent studies concerned with the extensive use of mass spectrometry for the structural analysis of recombinant proteins of pharmaceutical interest.

Characterization by mass spectrometry of a recombinant hepatitis delta virus antigen and its proteolytic products

The recombinant hepatitis delta virus antigen was obtained as a chimaeric protein fused to the C-terminus of the phage MS2 RNA polymerase. Following induction of the temperature-sensitive promoter, two major polypeptides of about 34 kDa and 29 kDa, and two minor peptides about 21 kDa and 18 kDa, were obtained on PAGE. The 34-kDa protein was identified as the expected recombinant protein by confirming 82% of the primary structure using fast-atom-bombardment mass spectrometry. The most represented degradation product, i.e. the 29-kDa polypeptide, was also characterized by means of mass spectrometry and found to be produced by cleavage between amino acids 261 and 265. The presence of two main protein bands, with a similar difference in size, is also a typical feature of delta antigens, both extracted and recombinant, and it is considered to be derived either from heterogeneity of viral sequences, which can encode hepatitis delta antigen proteins of 195 and 214 amino acids, or from proteolysis of a single precursor. Since the data were obtained with a single viral sequence coding for 195 amino acids fused to 106 residues from MS2 polymerase, there is direct evidence that intrinsic structural properties of the protein sequence are able to cause a specific proteolysis resulting in the presence of two major forms, of which the smaller is 35-40 amino acids at the C-terminus. The recombinant protein can be used as an antigenic substitute of viral antigens both for immunoassays and for the preparation of anti-(hepatitis delta virus) antisera.

River buffalo (Bubalus bubalis L.) AA phenotype haemoglobins: characterization by immobiline polyacrylamide gel electrophoresis and high performance liquid chromatography and determination of the primary structure of the constitutive chains by mass spectrometry

1. Polyacrylamide gel electrophoresis in ultra-narrow immobilized pH gradient shifted the "Hb fast" band of AA buffalo phenotype haemoglobin into two components which were named Hb1 and Hb3. 2. Urea/Triton electrophoresis and reversed-phase HPLC demonstrated that Hb1 and Hb3 differ in the presence of two structurally distinct alpha chains (alpha 1 and alpha 3), also suggesting that the alpha chains must differ for neutral amino acid substitution. 3. Extensive mass spectrometric analysis on several digests (FAB overlapping) meant to determine the complete sequence of the constituent chains. 4. Two amino acid replacements (Lys 18----His and Asn 116----His) were present in the beta chain with respect to the bovine (A phenotype) chain, whereas the alpha 1 and alpha 3 globins were found to contain four amino acid replacements compared to the bovine alpha, three of which were identical (Glu 23----Asp, Glu 71----Gly and Phe 117----Cys) and, notably, an insertion of Ala at position 123-124. 5. Furthermore, alpha 1 contains Phe at position 130 whereas alpha 3 contains Ser at position 132 (following the modified numbering as a consequence of the Ala insertion).

Single-step purification and structural characterization of human interleukin-6 produced in Escherichia coli from a T7 RNA polymerase expression vector

Human interleukin-6 or B-cell stimulatory factor-2 is a cytokine involved in acute phase and immune response. Cloning of cDNA for human interleukin-6 in the pT7.7 expression plasmid under the control of a bacteriophage T7 RNA polymerase promoter system allows rapid production of the cytokine in Escherichia coli. Upon cell induction with isopropyl thiogalactopyranoside, recombinant human interleukin-6 is overexpressed and forms insoluble inclusion bodies. Solubilization of the protein with 6 M guanidine hydrochloride and refolding in the presence of a reduction/oxidation system results in a quantitative recovery of recombinant human interleukin-6. This material is already 70% pure and can be further purified to homogeneity with a single passage over a weak anionic-exchange column. Extended structural characterization of the purified protein by electrospray mass spectrometry, automated Edman degradation and peptide mapping by high-pressure liquid chromatography/fast-atom-bombardment mass spectrometry demonstrates that recombinant human interleukin-6 is identical to the natural protein both in amino acid sequence and S-S bridge content. However, it contains a minor component accounting for about 20% of the entire translated protein which exhibits a Met-Ala dipeptide extension at the N-terminus. Purified recombinant human interleukin-6 is biologically active because it is able to induce at least 70-fold the human C-reactive promoter transfected in human hepatoma Hep 3B cells and is stable for several months in 10% glycerol at 4 degrees C. The expression system described in the present work has the main advantage of producing a high yield of recombinant human interleukin-6 (about 25 mg/l) combined with a very simple purification scheme.

Human alpha-fetoprotein primary structure: a mass spectrometric study

The amino acid sequence of human alpha-fetoprotein, a 67-kDa protein present in mammalian embryonic serum, was verified by fast atom bombardment mass spectrometric (FAB/MS) analyses of three different enzymatic digests of the protein. Human alpha-fetoprotein obtained from a large-scale cell culture was digested with trypsin and V-8 protease either separately on two different samples or combined on the same one. The V-8 protease digest of the protein was partially fractionated by HPLC; the other samples were directly analyzed by FAB/MS without previous purification steps. About 90% of the alpha-fetoprotein amino acid sequence was verified by mass spectrometric analysis; this also confirmed that the cell-derived protein is identical with the hepatoma-derived protein. FAB analysis revealed that the N terminus of the mature protein is arginine rather than threonine, with the threonine occupying the second position. Therefore, the processing site of the alpha-fetoprotein signal peptide during maturation of the protein occurs at the N-terminal side of the arginine residue formerly indicated as residue-1. Thus mature alpha-fetoprotein contains 591 amino acids rather than 590.

Capillary zone electrophoresis and mass spectrometry for the characterization of genetic variants of human hemoglobin

This paper describes a simple and rapid analytical method for the structural identification of abnormal human hemoglobins. Globin chains obtained by precipitation of erythrocyte hemolysate in cold acetone are directly analyzed by capillary zone electrophoresis in coated capillaries without any prior treatment. The speed and the high resolving power of capillary zone electrophoresis allow fast differentiation of hemoglobins with similar charges. Capillary zone electrophoretic tryptic mapping has also been performed for each globin, so that complete variant characterization can be achieved by direct comparison of the variant tryptic map with the corresponding normal one. Coupling electrophoretic data with analysis of enzymatic digests by mass spectrometry according to the "fast atom bombardment mapping" procedure makes it possible to quickly identify amino acid variations. This paper describes how the method can be applied to the characterization of common and uncommon variants and underlines the advantages and limitations of the procedure along with its potential uses in structural analysis of proteins.

Mass spectrometric identification of the amino donor and acceptor sites in a transglutaminase protein substrate secreted from rat seminal vesicles

Four different transglutaminase-modified forms of a protein secreted by the rat seminal vesicles (SV-IV) were synthesized in vitro and characterized. FAB maps of both the native protein and its derivatives, produced by the purified guinea pig liver enzyme in the presence or absence of the polyamine spermidine, were obtained by mass spectrometric analysis after proteolytic digestions. Two differently derivatized SV-IV molecular forms, both possessing only one glutamine residue out of two (Gln-86) cross-linked to endogenous lysine residues, were produced when spermidine was omitted from the reaction mixture: (i) an insoluble homopolymer in which Lys-2, -4, -59, -78, -79, and -80 were involved in the linkage; (ii) a soluble form of the protein with an intramolecular epsilon-(gamma-glutamyl)lysine isopeptide bond between Gln-86 and Lys-59. Two species of SV-IV-spermidine adducts were obtained when the protein was treated with transglutaminase in the presence of high concentrations of the polyamine. The first one was characterized by one spermidine molecule covalently bound to Gln-86 and the second one by two spermidine molecules respectively bound to Gln-9 and Gln-86.

A third instance of the high oxygen affinity variant, Hb Heathrow [beta 103(G5)Phe- greater than Leu]: identification of the mutation by mass spectrometry and by DNA analysis

Hb. Heathrow [beta 103(G5)Phe- greater than Leu] was identified in an Englishman with a life-long history of polycythemia, his father had been similarly affected. A hemoglobin variant was suspected from the high oxygen affinity of the patient's blood. The Hb Heathrow abnormal beta chain was resolved from the normal beta chain by high performance liquid chromatography, and the abnormal peptide and the amino acid replacement were identified by mass spectrometry. The corresponding base change (C- greater than G at codon 103) was demonstrated by sequence analysis of the polymerase chain reaction amplified exon 2 of the genomic beta-globin gene. This is only the third known instance of Hb Heathrow.

Fast atom bombardment mass spectrometric analysis of haemoglobin variants: use of V-8 protease in the identification of Hb M Hyde Park and Hb San Jose

The characterization of two human haemoglobin variants, Hb M Hyde Park and Hb San José, by fast atom bombardment mass spectrometry is reported. The identification of the site and nature of the amino acid substitution was performed by analysis of the peptide mixture generated by proteolytic digestion of the variant beta-globin chains with V-8 protease. The use of this protease was instrumental in the unambiguous identification of the replaced residues because the tryptic map alone was unable to unequivocally locate the modification. Spectra obtained were easily interpreted and the characterization of Hb M Hyde Park (beta, 92 Hys leads to Tyr) and Hb San José (beta 7 Glu leads to Gly) was accomplished essentially by the same procedure already described for the tryptic map. These results are suggestive of alternative approaches in haemoglobin variants characterization using different proteolytic enzymes when tryptic data alone do not lead to unambiguous results.

Mass spectrometric characterization of recombinant human interleukins 1 beta

The cDNA coding for amino acid residues 121-269 of human interleukin 1 beta was cloned and expressed at Sclavo Research Center by C. Baldari et al. (1987, EMBO J. 6, 229-234) using Saccharomyces cerevisiae as the host cell. The purified protein showed a very low specific activity when compared to that of a mature recombinant interleukin expressed from Escherichia coli. Preliminary experiments indicated the occurrence of post-translational events in the yeast-derived protein. In an attempt to correlate the structural modifications and the biological activity of recombinant interleukins, the two proteins were characterized by fast atom bombardment mass spectrometry (FAB/MS) following the FAB-mapping procedure. The amino acid sequence of interleukin expressed in E. coli was identical to that expected whereas the mass spectrometric analysis of the recombinant S. cerevisiae protein confirmed the occurrence of covalent modifications. In particular, the asparagine residue at position 7 (numbering follows the mature active protein sequence) was shown to be glycosylated and the two cysteine residues at position 8 and 71 were involved in an S-S bridge. The results demonstrate the value of FAB/MS in the quality control of recombinant interleukins.

The primary structure of papaya mosaic virus coat protein: a revision

The presence of an acetyl blocking group at the N-terminus of the coat protein of papaya mosaic virus has been identified by FAB mass spectrometry. Furthermore, we have found that the N-terminal sequence of the protein is four amino-acid residues (AC-Ser-Lys-Ser-Ser-) longer than that previously reported, while Glu instead of Gln is the C-terminal residue. The present paper shows that PMV-protein is made up of 215 amino acid residues, with a molecular mass of 22,960 Da.

Synthesis and characterization of a recombinant fragment of human alpha-fetoprotein with antigenic selectivity versus albumin

A DNA sequence coding for human alpha-fetoprotein amino acid sequence 38-119 was synthesized and cloned in a bacterial expression vector. The alpha-fetoprotein sequence was selected as the least homologous to albumin, since the two proteins have an overall amino acid identity of approximately 38%. A chimeric protein was obtained which was purified by preparative electrophoresis and characterized in its primary structure by fast atom bombardment mass spectometry. About 70% of the alpha-fetoprotein sequence was physically mapped and found to correspond to the amino acids encoded in the synthetic gene. The use of this recombinant protein allowed the selection of monoclonal antibodies recognizing both the recombinant fragment and native alpha-fetoprotein. These antibodies should allow the development of an immunoassay for alpha-fetoprotein with absolute selectivity versus albumin. This might result in more sensitive clinical determinations, avoiding the possibility of cross-reactions.

Characterization of abnormal human haemoglobins by fast atom bombardment mass spectrometry

A procedure using fast atom bombardment mass spectrometry for mapping the proteolytic digest of alpha-, beta- and gamma-globin chains of normal human haemoglobin was developed. It required the separation of globins prior to their analysis by mass spectrometry of their enzymatic digests. Almost all the expected peptides were identified by direct analysis of the peptide mixture. Peptide recognition along the globin chain sequences was easily made on the basis of their molecular weight and the assignments performed were confirmed submitting the whole peptide mixture to a single step of Edman degradation. The procedure was successfully applied to the structural characterization of three variant human beta-globin chains, demonstrating the general applicability of this mapping procedure in the analysis of haemoglobinopathies.

Fast atom bombardment (FAB) and chemical ionization (CI) mass spectrometry of γ-carboxyglutamic acid, 5-substituted-4,4-dicarboxyprolines, and their monodecarboxy derivatives glutamic acid and 5-substituted-4-carboxyprolines

DL-γ-Carboxyglutamic acid (Gla) reacts easily and quantitatively with aldehydes to give the racemic diastereoisomers of 5-substituted-4,4-dicarboxyprolines. After heating at 100 °C for 30 minutes these amino acids lose a carboxyl group from C-γ of Gla and C-4 of the proline ring to give glutamic acid and the racemic diastereoisomers of cyclic analogs of glutamic acid respectively. This paper reports a study of the above-mentioned compounds by using FAB mass spectrometry in comparison with CI analysis. FAB turned out to be an adequate ionization technique for dealing with such nonvolatile and thermolabile amino acids, and may thus allow the development of a rapid and sensitive method for detecting γ-carboxyglutamic acid in urine and in other biological matrices in pathological cases (i.e., renal stones and blood serum).

Substance P as a transglutaminase substrate: identification of the reaction products by fast atom bombardment mass spectrometry

Substance P was found to be an effective acyl donor substrate of transglutaminase in vitro, the reaction products having been examined by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fast atom bombardment mass spectrometry. Electrophoretic experiments showed that Substance P incorporated 14C-labeled polyamines when incubated with purified guinea pig liver transglutaminase and Ca2+. Extensive use of fast atom bombardment mass spectrometry allowed to establish that: i) a 1:1 adduct Substance P-spermine is formed; ii) only a single glutamine residue out of two, i.e. Gln-5, acts as acyl donor, iii) the single lysine residue of the neuropeptide is unable to act as acyl acceptor. A direct analytical methodology to detect transglutaminase reaction products is described.

Beta-endorphin modification by transglutaminase in vitro: identification by FAB/MS of glutamine-11 and lysine-29 as acyl donor and acceptor sites

FAB-Mapping strategy was successfully exploited to characterize the reaction products of the transglutaminase-mediated modifications of human beta-endorphin in vitro. The GLN-11 residue of the neuropeptide was shown to be an effective acyl donor site for the enzyme, being able to bind spermine in the presence of Ca2+. Moreover, only one out of five lysyl residues (LYS-29) was demonstrated to act as acyl acceptor crosslinking with GLN-11.

Identification by fast atom bombardment mass spectrometry of Hb Indianapolis [beta 112(G14)Cys----Arg] in a family from Naples, Italy

We have characterized a beta 112 Arg hemoglobin in an individual from Naples, Italy, with minimal clinical problems. Blood tests revealed only slight reticulocytosis and hemoglobin instability. Furthermore, high value of alkali resistance tests for Hb F were observed. Isoelectricfocusing of globins showed the occurrence of a band migrating between the normal alpha and beta globin chains. The fairly stable variant chain was purified by fast protein liquid chromatography. A mass map of the tryptic digest was obtained by fast atom bombardment mass spectrometry clearly showing that we were dealing with a beta chain variant. However, the peptide 105-120 was missing and two new ones were present, i.e.: 105-112 and 113-120; we assumed these peptides to be generated because of the substitution of 112 Cys with an arginine residue. Further confirmation stemmed from the fast atom bombardment mass spectra of the tryptic digest submitted to a single Edman degradation step and to carboxypeptidase B further hydrolysis. The beta-globin chain variant was thus mass mapped to an extent of about 98%. Such a variant, named Hb Indianapolis, was first reported by Adams et al, as an extremely unstable variant producing the phenotype of a severe beta-thalassemia. Contrary to the findings of the above authors the occurrence of the same variant in a clinically normal individual from a Spanish family has recently been reported. Because the clinical manifestations in the latter case are similar to those observed by us, the conclusion can be drawn that beta 112 Arg hemoglobin is not a biologically unstable variant but should be regarded as belonging to the class of unstable hemoglobins giving rise to only marginal clinical problems.

Effect of matrix modification by strong mineral acids on the positive fast atom bombardment mass spectra of peptides

We report an investigation of the effect of the addition of strong mineral acids to the most commonly used matrices for fast atom bombardment mass spectrometry of peptides. Among the acids tested we found that perchloric acid has a beneficial effect on: the sensitivity, the stability of quasi-molecular ion signals. Furthermore, in the presence of basic residues, ions related to perchlorate adducts are present. These further signals may be useful in differentiating peptides containing lysine from those containing the isobaric glutamine.

[Extraction of fecal lipids and identification of hydroxystearic acid by gas chromatography-mass spectrometry (GC/MS)]

Fatty acids and hydroxy fatty acids in the intestine are of interest because of their cathartic properties. We describe a method for extraction of lipids from freeze dried homogenized stools and identification of the hydroxy stearic acid in the fecal lipids pattern by GC-MS. Recovery of 90-95 % shows the efficacy of extraction . Quantitative data of fecal hydroxy stearic acid excretion in some normal and chronic diarrhea affected children are reported.

[A new method of quantitative analysis of bicarboxylic acids by means of gas chromatography]

A new method for the quantitative extraction and esterification of dicarboxylic organic acids in aqueous solution and biological fluids has been developed. The acids are extracted and esterified in one step by using an Amberlite IRA 904 anion exange resin. The analyses of the methyl esters obtained have been performed by gas-liquid chromatography.