Protein fingerprint by fast atom bombardment mass spectrometry: characterization of normal and variant human haemoglobins

Hemoglobin Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)]: a mosaic to be put together

OBJECTIVES

Artifactually altered glycated hemoglobin (HbA_1c) concentrations are frequently linked to hemoglobin (Hb) variants. Their expression and detection require in-depth analysis.

METHODS

Cation exchange high performance liquid chromatography (HPLC) (Bio-Rad Variant™ II; Trinity Biotech Premier Hb9210 Resolution), capillary electrophoresis (CE) (Sebia Capillarys 2 Flex Piercing) and mass spectrometry (MS) (Waters) were used for variant detection; Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) were used for DNA analysis; HbA_1c was measured with cation exchange HPLC (Bio-Rad Variant™ II; Arkray Adams HA-8180V; Tosoh HLC-723 G7), CE (Sebia Capillarys 2 Flex Piercing), boronate affinity HPLC (Trinity Biotech Hb9210 Premier), immunoassay (Cobas c501 Tina-quant HbA_1c Gen. 3; Nihon Kohden CHM-4100 Celltac chemi HbA_1c HA-411V) and enzymatic assay (Abbott Architect c 8000 HbA_1c).

RESULTS

Hb Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)] was identified in the proband by MS after the observation of an abnormal peak in HPLC and CE. A mosaic expression of this variant was detected by NGS (mutant: 8%; wild type: 92%), after negative results in Sanger sequencing. Hb Yamagata interfered with HbA_1c measurements by cation exchange HPLC and CE whereas immuno and enzymatic assay values showed good agreement with boronate affinity HPLC measurement.

CONCLUSIONS

A mosaicism of Hb Yamagata was found in a patient with altered HbA_1c values. This rare gene variant was detected only by advanced technologies as MS and NGS. The variant interfered with common HbA_1c determination methods.

MALDI-ISD Mass Spectrometry Analysis of Hemoglobin Variants: a Top-Down Approach to the Characterization of Hemoglobinopathies

Hemoglobinopathies are the most common inherited disorders in humans and are thus the target of screening programs worldwide. Over the past decade, mass spectrometry (MS) has gained a more important role as a clinical means to diagnose variants, and a number of approaches have been proposed for characterization. Here we investigate the use of matrix-assisted laser desorption/ionization time-of-flight MS (MALDI-TOF MS) with sequencing using in-source decay (MALDI-ISD) for the characterization of Hb variants. We explored the effect of matrix selection using super DHB or 1,5-diaminonaphthalene on ISD fragment ion yield and distribution. MALDI-ISD MS of whole blood using super DHB simultaneously provided molecular weights for the alpha and beta chains, as well as extensive fragmentation in the form of sequence defining c-, (z + 2)-, and y-ion series. We observed sequence coverage on the first 70 amino acids positions from the N- and C-termini of the alpha and beta chains in a single experiment. An abundant beta chain N-terminal fragment ion corresponding to βc34 was determined to be a diagnostic marker ion for Hb S (β6 Glu→Val, sickle cell), Hb C (β6 Glu→Lys), and potentially for Hb E (β26 Glu→Lys). The MALDI-ISD analysis of Hb S and HbSC yielded mass shifts corresponding to the variants, demonstrating the potential for high-throughput screening. Characterization of an alpha chain variant, Hb Westmead (α122 His→Gln), generated fragments that established the location of the variant. This study is the first clinical application of MALDI-ISD MS for the determination and characterization of hemoglobin variants.

HB City of Hope [β69(E13)GLY→SER] in Italy: Association of the Gene with Haplotype IX

Hb City of Hope [beta 69(E13)Gly----Ser] was detected by reversed phase high performance liquid chromatography in an asymptomatic carrier from Naples, Southern Italy. The amino acid substitution, identified by fast atom bombardment mass spectrometry, was due to a TGG----TGA substitution as assessed by DNA sequencing. Analysis of the chromosomal background indicates that the globin gene cluster containing the mutant gene has most probably been rearranged by a recombination event, since the mutation was associated with restriction fragment length polymorphism haplotype IX, instead of haplotype I, as previously reported.

Characterization of the 12% trichloroacetic acid-insoluble oligopeptides of Parmigiano-Reggiano cheese

The isolation and identification of low molecular mass peptides formed during the ripening of Parmigiano-Reggiano cheese is described. A strategy was used based on the fractionation of nitrogenous material using chemical methods followed by HPLC to isolate peptides and fast atom bombardment-mass spectrometry to identify them. It was found that the majority of cheese oligopeptides arose from the proteolysis of β-casein. Several phosphopeptides and oligopeptides known in vivo to be biologically active have also been identified during the ripening of cheese.

Ion trap collision-induced dissociation of human hemoglobin alpha-chain cations

Multiply protonated human hemoglobin alpha-chain species, ranging from [M + 4H]4+ to [M + 20H]20+, have been subjected to ion trap collisional activation. Cleavages at 88 of the 140 peptide bonds were indicated, summed over all charge states, although most product ion signals were concentrated in a significantly smaller number of channels. Consistent with previous whole protein ion dissociation studies conducted under similar conditions, the structural information inherent to a given precursor ion was highly sensitive to charge state. A strongly dominant cleavage at D75/M76, also noted previously in beam-type collisional activation studies, was observed for the [M + 8H]8+ to [M + 11H]11+ precursor ions. At lower charge states, C-terminal aspartic acid cleavages were also prominent but the most abundant products did not arise from the D75/M76 channel. The [M + 12H]12+-[M + 16H]16+ precursor ions generally yielded the greatest variety of amide bond cleavages. With the exception of the [M + 4H]4+ ion, all charge states showed cleavage at the L113/P114 bond. This cleavage proved to be the most prominent dissociation for charge states [M + 14H]14+ and higher. The diversity of dissociation channels observed within the charge state range studied potentially provides the opportunity to localize residues associated with variants via a top-down tandem mass spectrometry approach.

On-probe digestion of bacterial proteins for MALDI-MS

On-probe digestion combined with MALDI mass spectrometry is studied as a rapid method for the analysis and identification of bacterial proteins. The use of trypsin adsorbed to the probe surface reduces the digestion time from hours to minutes. A high amount of trypsin must be applied to the probe for the successful digestion of bacterial proteins. Mass spectra of the digest contain a number of low-mass digest fragments. Several components of a B. subtilis bacterial digest can be identified through postsource decay and database searching.

Some aspects of matrix-assisted laser desorption/ionization analysis of hemoglobin from whole human blood

Some aspects of the matrix-assisted laser desorption/ionization (MALDI) method in the analysis of hemoglobin from whole human blood are described. These aspects are: sensitivity of this method, fragmentation of hemoglobin ions, and influence of some impurities (sodium chloride NaCl, sodium sulfate Na2SO4, and potassium ferrocyanide K4Fe(CN)6) on the detection process. As a matrix, alpha-cyano-4-hydroxycinnamic acid (CCA) was used. The estimated maximum concentrations of tested salts for which no hemoglobin signal was observed were determined.

Primary structure of alpha-globin chains from river buffalo (Bubalus bubalis L.) hemoglobins

Primary structure analysis of the four river buffalo alpha-globin chains showed that haplotypes A and B differ from each other by a substitution at codon 64 that may encode Ala or Asn. The A haplotype encodes two alpha-globin chains, Ialpha1 and IIalpha3, which differ at positions 129 and 131: Ialpha1 has 64 Ala, 129 Phe, 131 Asn; IIalpha3 has 64 Ala, 129 Leu, 131 Ser. The B haplotype encodes two alpha-globin chains, Ialpha2 and IIalpha4, which differ at positions 10 and 11: Ialpha2 has 10 I1e, 11 Gln, 64 Asn; IIalpha4 has 10 Val, 11 Lys, 64 Asn. Apart from the Ala/Asn polymorphism at position 64, amino acid substitutions in allelic and nonallelic alpha-globin chains seem to have arisen by single point mutations. Detection of electrophoretically silent mutations due to neutral amino acid substitutions and their influence on the isoelectric point are discussed. Furthermore, primary structures of river buffalo alpha-globin chains are compared to other species of the Bovidae family to suggest evolutionary events that have characterized the amino acid substitutions of river buffalo hemoglobin.

Electrospray tandem mass spectrometry in the rapid identification of alpha-chain haemoglobin variants

The potential use of electrospray tandem mass spectrometry in the rapid characterisation of haemoglobin variants found in the Swedish population has been assessed. Analysis times of the order of 5 -10 min were routinely achieved, and identification of variants using mass spectrometry as the sole analytical technique was possible. However, additional information, readily available from isoelectric focusing experiments, made identification simpler and more secure. In the present communication we report on the identification of the alpha-chain variants, Hb Russ, Hb Le Lamentin and Hb Q-Iran. The identifications were confirmed by the use of nucleotide sequencing techniques.

Toward a simple, expedient, and complete analysis of human hemoglobin by MALDI-TOFMS

MALDI mass spectrometry is explored as a method for hemoglobin characterization. To simplify and expedite the analysis, hemoglobin is obtained without purification directly from whole human blood. The use of trypsinactivated bioreactive MALDI probes is evaluated as a means to further reduce the analysis time from hours to minutes. Moreover, variations of the MALDI matrix preparation facilitate detection of the problematic tryptic peptides alpha T12, alpha T13, and beta T12. The results reveal that MALDI-based methods are easily implemented, are rapid, and allow detection of traditionally elusive tryptic peptides.

Iron superoxide dismutase from the archaeon Sulfolobus solfataricus: average hydrophobicity and amino acid weight are involved in the adaptation of proteins to extreme environments

The iron-superoxide dismutase in the thermoacidophilic archaeon Sulfolobus solfataricus has a homodimeric structure with a metal content of 0.7 atom of iron per subunit. The enzyme is insensitive to cyanide inhibition, sensitive to inactivation by H2O2 and is the most heat resistant SOD known so far being its half-life 2 h at 100 degrees C. Its primary structure was determined by a profitable combination of advanced mass spectrometry and automated sequence analysis of peptides obtained after cleavage of the purified protein. The enzyme subunit is composed of 210 amino acid residues accounting for a relative molecular mass of 24,112. It does not contain cysteine residues and has a high average of both hydrophobicity and amino acid weight. Vice versa, the hydrophobicity is lower in halophilic SODs. Therefore, it seems that the average hydrophobicity is involved in the adaptation of proteins to extreme environments. The multiple alignment of the primary structure of archaeal and thermophilic eubacterial SODs indicated that archaeal SODs evolved separately from the thermophilic eubacterial SODs and that halophiles originated from a gene different from that of thermophilic archaea.

Identification of hormonogenic tyrosines in fragment 1218-1591 of bovine thyroglobulin by mass spectrometry. Hormonogenic acceptor TYR-12donor TYR-1375

A fragment of bovine thyroglobulin encompassing residues 1218-1591 was prepared by limited proteolysis with thermolysin and continuous-elution polyacrylamide gel electrophoresis in SDS. The reduced and carboxymethylated peptide was digested with endoproteinase Asp-N and fractionated by reverse-phase high performance liquid chromatography. The fractions were analyzed by electrospray and fast atom bombardment mass spectrometry in combination with Edman degradation. The post-translational modifications of all seven tyrosyl residues of the fragment were characterized at an unprecedented level of definition. The analysis revealed the formation of: 1) monoiodotyrosine from tyrosine 1234; 2) monoiodotyrosine, diiodotyrosine, triiodothyronine (T3), and tetraiodothyronine (thyroxine, T4) from tyrosine 1291; and 3) monoiodotyrosine, diiodotyrosine, and dehydroalanine from tyrosine 1375. Iodothyronine formation from tyrosine 1291 accounted for 10% of total T4 of thyroglobulin (0.30 mol of T4/mol of 660-kDa thyroglobulin), and 8% of total T3 (0.08 mol of T3/mol of thyroglobulin). This is the first documentation of the hormonogenic nature of tyrosine 1291 of bovine thyroglobulin, as thyroxine formation at a corresponding site was so far reported only in rabbit, guinea pig, and turtle thyroglobulin. This is also the first direct identification of tyrosine 1375 of bovine thyroglobulin as a donor residue. It is suggested that tyrosyl residues 1291 and 1375 may support together the function of an independent hormonogenic domain in the mid-portion of the polypeptide chain of thyroglobulin.

Transglutaminase from rat coagulating gland secretion. Post-translational modifications and activation by phosphatidic acids

Structural and biochemical characteristics of transglutaminase purified by a rapid chromatographic procedure from the rat coagulating gland (anterior prostate) secretion are reported. Fast atom bombardment mapping and automated Edman degradation experiments allowed us to verify that at least 85% of the entire transglutaminase amino acid sequence is identical to that derived from the cDNA of the major androgen-dependent rat prostate protein called DP1. The enzyme was found NH2 terminally blocked and largely post-translationally modified, since the presence of N-linked oligosaccharides, as well as of complex lipidic structures, was observed. Mass spectral analysis showed that Asn-408 and -488 are the glycosylated sites, the N-linked structures identified belonging to both high-mannose and complex type glycans. The presence of myo-inositol, of glycerol bound fatty acids, and the high content of mannose residues, are in agreement with previous observations suggesting that a lipid anchor is bound to coagulating gland secretion transglutaminase. Furthermore, two tightly bound calcium ions per molecule of enzyme were detected. Finally, a strong stimulation of the enzyme activity in vitro by both SDS and a variety of phosphatidic acids was observed. The reported structural and functional peculiarities should definitively lead to consider the prostate enzyme as a new member (type IV) of the transglutaminase family.

Amino acid sequence and molecular modelling of glycoprotein IIb-IIIa and fibronectin receptor iso-antagonists from Trimeresurus elegans venom

Low-molecular-mass Arg-Gly-Asp (RGD)-containing polypeptides were isolated from the venom of Trimeresurus elegans by a simple two-step procedure consisting of membrane filtration and reverse-phase HPLC. A combination of electrospray MS, fast-atom bombardment MS and Edman degradation allowed us to ascertain the presence in the venom of different isoforms and to determine their primary structures. The amino acid sequences resembled the structure of elegantin, the only disintegrin previously reported from the T. elegans venom [Williams, Rucinski, Holt and Niewiarowski (1990) Biochim. Biophys, Acta 1039, 81-89]. MS analyses indicated the occurrence of differential proteolytic processing at both the N-terminus and the C-termins of the polypeptide chains. The amino acid sequence alignment of the elegantin isoforms with known components of the disintegrin family demonstrated the complete conservation of the 12 cysteine residues involved in disulphide bridges. Molecular modelling of elegantins predicted an overall folding of these molecules quite similar to that reported for the kistrin solution structure. The newly identified polypeptide isoforms strongly inhibited ADP-induced aggregation in both human and canine platelet-rich plasma but showed a different species-dependent specificity. These molecules were also able to inhibit B16-BL6 murine melanoma cell adhesion to immobilized fibronectin. The comparison of the structures and biological activities of elegantin isoforms and kistrin allowed us to highlight some structural features that, in addition to the RGD locus might be involved in the interaction of these snake-venom polypeptides with the integrin receptors on the platelet and cell surface.

Electrospray ionization-tandem mass spectrometry analysis of peptides derived by enzymatic digestion of oxidized globin subunits: An improved method to determine amino acid substitution in the hemoglobin "core"

The determination of an amino acid substitution in the "core" region of abnormal hemoglobin is technically difficult and is time- and labor-intensive both by conventional and by mass spectrometry techniques. Underivatized subunits cleaved with trypsin and lysyl endopeptidase were analyzed by high-performance liquid chromatography-electrospray ionizationmass spectrometry. The core peptides showed a series of multiply charged ions of homo- and heterodimers. Abnormal peptides in the core region could be detected in dimeric form. The sequence of core peptides was determined by product ion spectra of the peptides from oxidized globin digested with trypsin and lysyl endopeptidase. Oxidation of cysteine residues to cysteic acids in the core region resulted in the strong promotion of y-series ions by product ion analysis with a tryptic peptide from apoprotein B-100 as previously reported by Burlet, Yang, and Gaskell (J. Am. Soc. Mass Spectrom. 1992, 3, 337-344). These techniques were used to prove that substitution of an unstable hemoglobin, known as Hb Santa Ana (β88 leucine → proline), occurred in a patient with congenital hemolytic anemia. The tandem mass spectrometry analysis with oxidized globin digested with trypsin and lysyl endopeptidase offers a novel method to detect substitutions in the core region of hemoglobin.

The gene, protein and glycan structures of laccase from Pleurotus ostreatus

A member of the laccase multigene family in Pleurotus ostreatus has been cloned and sequenced. The gene structure has been determined by comparison with the corresponding cDNA, synthesized by reverse transcription/PCR amplification. The gene encode a laccase isoenzyme of 533 amino acids which has already been purified and characterized [Palmieri, G., Giardina, P., Marzullo, L., Desiderio, B., Nitti, G., Cannio, R. & Sannia, G.(1993) Appl. Microbiol. Biotechnol. 39, 632-636]. More than 92% of the protein sequence, including the N and C termini, has been verified by fast-atom-bombardment mass spectrometry, thus confirming the correspondence between the gene and its protein product. The protein was N-glycosylated Asn444. Glycan analysis showed the presence of only a high-mannose structure containing varying numbers of mannose residues. The presence of O-linked oligosaccharides as well as other post-translational modification could be ruled out by the mass analysis.

Use of combined mass spectrometry methods for the characterization of a new variant of human hemoglobin: The double mutant hemoglobin villeparisis β77(EF1) His → Tyr, β 80 (EF4) Asn → Ser

Hemoglobin Villeparisis was found during a systematic measurement of glycated hemoglobin. Electrospray mass spectra of the globin indicate an apparently unchanged molecular weight within the error range (0.01%). The tryptic digest of the β chain shows a chromatographically abnormal βT-9 peptide. The mass-to-charge ratio value of its [M+H](+) ion, as measured by liquid secondary ionization mass spectrometry, is one mass unit lower than that of the normal βT-9. However, the electrospray mass spectrum of this peptide exhibits mainly a doubly charged ion, whereas the normal βT-9 gives a triply charged ion. None of the allowed single amino acid substitutions for a 1-u shift down (Glu → Gln, Asp → Asn, or Asn → Ile) can explain the suppression of one protonation site. This can be due only to the replacement of the internal histidine by a nonbasic residue. Thus at least two amino acid exchanges occur within the same peptide: one involves the internal histidine, and the sum of the mass shifts is -1 u. Consideration of the βT-9 sequence and taking account for the genetic code rules, the only possibility was (11)His → Tyr (+26 mass shift) associated with (14)Asn → Ser (-27 mass shift). This conclusion was consistent with the tandem mass spectrum of the [M+H](+) ion and was further confirmed by chemical microsequencing.

Primary structure of ovine alpha s1-caseins: localization of phosphorylation sites and characterization of genetic variants A, C and D

The primary structures of ovine alpha s1-casein variants A, C and D (formerly called Welsh variant) were determined. Separation of variants from whole casein was achieved using a fast and reliable reversed-phase HPLC method. Extended structural characterization of the purified proteins using electrospray mass spectrometry, automated Edman degradation and peptide mapping by means of HPLC-fast atom bombardment-mass spectrometry demonstrated that the mature protein was a mixture of two molecular species that differed in the deletion of residues 141-148 and were therefore 199 and 191 residues long respectively. The 199 residue peptide chain, which accounted for approximately 80% of the entire translated alpha s1-casein, was as long as its caprine and bovine counterparts, and had a 98 and 89% degree of identity with those two proteins respectively. Nine serine residues (positions 12, 44, 46, 64 to 68 and 75) were fully phosphorylated in alpha s1-casein A, whereas Ser115 and Ser41 were phosphorylated by approximately 50 and approximately 20% respectively. The differences between the three genetic variants A, C and D were simple silent substitutions, which however involved the degree to which the protein was phosphorylated. Variant C differed from variant A in the substitution Ser13-->Pro13 which determined the loss of the phosphate group on site 12 of the protein chain, SerP12-->Ser12. A further substitution, SerP68-->Asn68 caused the disappearance of both phosphate groups in the phosphorylated residues Ser64 and Ser66 in variant D; in this last casein variant there was no evidence of phosphorylation at Ser41.

Structural analysis of saposin C and B. Complete localization of disulfide bridges

Saposins A, B, C, and D are a group of homologous glycoproteins derived from a single precursor, prosaposin, and apparently involved in the stimulation of the enzymatic degradation of sphingolipids in lysosomes. All saposins have six cysteine residues at similar positions. In the present study we have investigated the disulfide structure of saposins B and C using advanced mass spectrometric procedures. Electrospray analysis showed that deglycosylated saposins B and C are mainly present as 79- and 80-residue monomeric polypeptides, respectively. Fast atom bombardment mass analysis of peptide mixtures obtained by a combination of chemical and enzymatic cleavages demonstrated that the pairings of the three disulfide bridges present in each saposin are Cys4-Cys77, Cys7-Cys71, Cys36-Cys47 for saposin B and Cys5-Cys78, Cys8-Cys72, Cys36-Cys47 for saposin C. We have recently shown that saposin C interacts with phosphatidylserine-containing vesicles inducing destabilization of the lipid surface (Vaccaro, A. M., Tatti, M., Ciaffoni, F., Salvioli, R., Serafino, A., and Barca, A. (1994) FEBS Lett. 349, 181-186); this perturbation promotes the binding of the lysosomal enzyme glucosylceramidase to the vesicles and the reconstitution of its activity. It was presently found that the effects of saposin C on phosphatidylserine liposomes and on glucosylceramidase activity are markedly reduced when the three disulfide bonds are irreversibly disrupted. These results stress the importance of the disulfide structure for the functional properties of the saposin.

Post-translational modifications in aspartate aminotransferase from Sulfolobus solfataricus. Detection of N-epsilon-methyllysines by mass spectrometry

Advanced mass spectrometric procedures have been extensively used to provide an accurate structural characterization of aspartate aminotransferase from Sulfolobus solfataricus. The amino acid sequence of this enzyme had previously been deduced from the DNA sequence. The accurate molecular mass of the protein, determined using electrospray mass spectrometry, demonstrated that the amino acid sequence deduced was correct and ruled out the possible presence of large covalent modifications which had been postulated to fit the much higher molecular mass obtained from previous SDS/PAGE experiments. The definition of the entire primary structure of aspartate aminotransferase from S. solfataricus was achieved by exploiting a new mass spectrometric mapping strategy. Initially, the molecular mass of relatively large protein fragments produced by CNBr hydrolysis was accurately determined using electrospray mass spectrometry. The protein regions where structural modifications had occurred were easily identified from their anomalous mass values. The corresponding CNBr fragments were then subdigested with suitable proteases and the resulting peptide mixtures were analysed by fast-atom-bombardment mass spectrometry. This mapping approach led to the detection of two partially modified lysine residues at positions 202 and 384, which had been converted to their N-epsilon-methyl derivatives to a substoichiometric extent.

Mass spectrometric analysis of rat hemoglobin by FAB-overlapping. Primary structure of the alpha-major and of four beta constitutive chains

1. The globin chain components of Sprague-Dawley rat hemoglobin were obtained by reverse-phase HPLC which showed the presence of two alpha-chain and four beta-chains. 2. The accurate molecular weight of each globin chain was determined by means of electrospray mass spectrometry. Extensive mass spectrometric analysis on several enzymatic digests by fast atom bombardment mass spectrometry (FAB-overlapping) meant to determine the complete sequence of the alpha-major and of the four beta-globins. 3. The primary structure of the alpha-major globin was found in agreement with literature data (Garrick et al., 1975 Biochem. J. 149, 245-258; Chua et al., 1987). 4. Sequence analysis of the four beta-globin chains showed that amino acid differences are restricted to two protein portions: the region 22-25 and 123-125, the remaining portions of the molecule being unchanged in the four globins. Furthermore, all the amino acid replacements correspond to single point DNA mutations and (with the exception of the substitution Asp 22-->Asn in the beta 2-globin) involve uncharged substitutions.

Hb O-Arab [beta 121(GH4)Glu-->Lys]: association with DNA polymorphisms of African ancestry in two Mediterranean families

Hb O-Arab [beta 121(GH4)Glu-->Lys] was detected in two Mediterranean families, one from Southern Italy and the other from Albania. The GAA-->AAA mutation at codon 121 was characterized by DNA sequencing. The mutant genes were associated with the same beta-globin gene framework variant and with the rare Hpa I/3' beta polymorphic restriction site generating a 7.0 kb fragment. However, at 5' the gene of the Italian family was associated with the restriction fragment length polymorphism subhaplotype [+ - - - +] and the Taq I/3'G gamma polymorphic site, while that of the Albanian family was associated with subhaplotype [- - - - +] but not with the Taq I/3'G gamma site. The particular features of these polymorphisms support the hypothesis of an African origin for the Hb O-Arab gene and a subsequent recombination event leading to the haplotype found in the Italian family.

Electrospray mass spectrometric analysis of river buffalo (Bubalus bubalis) hemoglobins. Re-examination of alpha 1 and alpha 3 globin chain sequences

1. The accurate molecular weight of the globin chains from river buffalo hemoglobin components has been determined by means of electrospray mass spectrometry. 2. The ES/MS analysis demonstrated that all the buffalo Hb components share a common beta chain whose mass value coincides with that expected on the basis of the reported sequence. 3. The AA phenotype alpha 1 and alpha 3 globin chains exhibited a 30 Da mass difference as compared to their predicted molecular weights. Careful re-examination of the two alpha globin sequences by FAB/MS revealed the occurrence of sequence errors and hence the correct primary structure of both alpha chains was established.

Expediting rare variant hemoglobin characterization by combined HPLC/electrospray mass spectrometry

Microscale analysis of a variant hemoglobin (Hb) has been achieved by combination of high performance liquid chromatography (HPLC) and electrospray mass spectrometry (ESMS) and the method should be almost universally applicable. We have eliminated preparative scale HPLC of globin chains and semi-preparative HPLC of proteolytic digests which had been used prior to mass spectrometry. Use of microbore HPLC columns reduced the time required for analysis substantially and solvent usage by 100x. Molecular masses of intact globins and masses and sequence information of tryptic peptides could be obtained without collecting and separately analyzing chromatographic fractions. As an example of the use of these methods, we report the characterization of an unknown hemoglobinopathy case that was finally authenticated as Hb P-Galveston [beta 117(G19)His-->Arg], using the following sequence of analyses: 1) ESMS of complete hemolysate, 2) analytical HPLC of globin chains, 3) combined microbore HPLC/ESMS of globin chains to determine their molecular masses, 4) cysteine derivatization and tryptic digestion of mixture of all globins, followed by microbore separation of the peptides, molecular mass determination, and generation of fragmentation patterns allowing confirmation of amino acid sequences. This four-part strategy should allow characterization of almost all variant Hbs. Exceptions would be mutations in regions of globin chains which give rise to small (< four residues) tryptic peptides, either normal or produced by addition of new tryptic sites and mutations that introduce only minute difference in molecular weight (MW) of tryptic peptides. Since only 10% of each separated peptides is mass analyzed, 90% is available for collection and further structural identification (e.g. by tandem MS or Edman sequencing) if the identity is still in doubt.

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).

Plasma desorption mass spectrometry of haemoglobin tryptic peptides for the characterization of a Hungarian alpha-chain variant

S-Aminoethylated-alpha A and -beta A globin tryptic peptides separated by reversed-phase high-performance liquid chromatography have been analysed by plasma desorption mass spectrometry. Almost all the expected alpha A and beta A tryptic fragments were tentatively assigned relative to the known globin chain sequences based on the molecular weight obtained by plasma desorption mass spectrometric analysis of the purified peptides. The application of plasma desorption mass spectrometry for structure elucidation of a haemoglobin alpha-chain variant revealed the first case of Hb Hasharon in Hungary.

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.

A new procedure for peptide alignment in protein sequence determination using fast atom bombardment mass spectral data

A computer program allowing the correct alignment of peptides generated by a first cleaving agent during protein sequence determination studies has been developed. The program elaborates data obtained from fast atom bombardment mass spectrometric analysis of different digests of the protein. The recorded mass values are used to identify peptides in these digests that overlap peptides from the first cleavage, thus making it possible to establish unambiguously the correct order of these peptides in the protein chain. This procedure has been tested on a model protein by reconstructing the complete sequence of human beta-globin chain, determining the correct alignment of 14 tryptic peptides.

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.

New results of hemoglobin variant structure determinations by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry has already been used for the identification of mutations in abnormal human hemoglobin chains. This paper presents new results obtained with this technique. The methodology used here is compared with more conventional biochemical techniques and automated microsequencing. In every case, a well-chosen combination of peptide-high performance liquid chromatography, mass spectrometry, amino acid analysis, and sequence analysis led rapidly to the identification of the mutant. The high sensitivity of these techniques holds great promise for the analysis of molecular abnormalities in various genetic disorders presently detectable only by the application of a molecular biological approach.

Characterization of Hb Aalborg, a new unstable hemoglobin variant, by fast atom bombardment mass spectrometry

Hb Aalborg is a new unstable hemoglobin variant found in association with mild anemia. Heinz bodies were readily inducible in red cells but there was no specific evidence of hemolysis and the variant therefore appears to be without significant clinical effect. The amino acid replacement was identified by fast atom bombardment mass spectrometry and is that of Gly----Arg at position beta 74 (E18). Hb Aalborg is moderately unstable.

Rapid determination of sequence variations in actinidin isolated from Actinidia chinensis (var. Hayward) using fast atom bombardment mapping mass spectrometry and gas phase microsequencing

A current limitation in the use of fast atom bombardment (FAB) mass spectrometric mapping of peptide mixtures, derived from enzymic digestion of proteins, is that most of the hydrophilic peptides are not observed. However, it has been demonstrated from previous work that esterification of the peptide mixture results in the detection of almost all peptides in FAB mass spectrometry. This strategy of FAB mapping was applied to the protein actinidin, isolated from an Italian variety of Actinidia chinensis. Two of the 12 tryptic peptides in FAB mass spectrometry did not exhibit molecular ions predicted from the known sequence of actinidin isolated from the New Zealand variety of A. chinensis. The two peptides were isolated by high-performance liquid chromatography, subjected to Staphylococcus aureus V8 protease digestion and sequenced by gas-phase microsequencing. Nine changes in amino acid composition were detected using the rapid and powerful combination of FAB mass spectrometric mapping and gas-phase microsequencing.

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.

Identification of some abnormal haemoglobins by fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry

The characterization of two abnormal human haemoglobins by fast atom bombardment (FAB) mapping is presented. The first variant, called 'R', exhibits a tryptic FAB map identical to that of normal haemoglobin. However, using Staphylococcus protease V8, a peptide containing the carboxyl end of the beta-chain exhibits a mass shift down to 300 mass units. This clearly indicates the deletion of the two last amino acids of the beta-chain. The second variant, called 'Grenoble', is due to two different modifications of the beta-chain. The location of the Pro----Ser exchange on peptide T5 is achieved by the collisionally activated dissociation mass analyzed ion kinetic energy spectra of the corresponding [MH]+ ion. The m/z value of that peptide indicated a supplementary acid----amide modification, which was located by amino acid sequencing using chemical methods. This work concludes with the necessity of using complementary methods for achieving rapid determinations of abnormal proteins with minute amounts.

Identification of iodination sites in cytochrome c by high-performance liquid chromatography and fast atom bombardment mass spectrometry

Site-directed covalent modification of proteins is currently used to study the molecular structure of enzyme active sites. Radioactive labels together with protein sequencing by Edman degradation have been previously employed to identify the site of modification. One drawback of such a procedure is that most reagents are not commercially available in radioactive form. Moreover, the covalent bond formed upon reaction of the label with the protein may be labile under the conditions of Edman degradation. By combining reverse-phase high-performance liquid chromatography (RP-HPLC) and fast atom bombardment (FAB) mass spectrometry, we have been able to identify the modified sites of horse heart cytochrome c after reaction with iodine. By using this procedure it has been possible to ascertain that, among the four tyrosines contained in the sequence of horse heart cytochrome c, only tyrosine 74 is converted into the monoiodinated derivative. The data demonstrate also the absence of unwanted secondary reactions. The technique avoids the use of radioactive materials and prevents losses of the label since Edman degradation is not required to identify the modified peptides. These results indicate that FAB mass spectrometry along with RP-HPLC is potentially a powerful technique to study chemical modifications of proteins.

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.

Reverse phase high-performance liquid chromatography and secondary ion mass spectrometry. A strategy for identification of ten human hemoglobin variants

Ten abnormal hemoglobins were detected and characterized in individual cases referred to our laboratory for evaluation of hematological problems. Six of these variants were electrophoretically silent and could be detected by reverse phase high-performance liquid chromatography (HPLC) analysis. HPLC was also used to analyze the tryptic peptides of each individual variant. In most of these variants, secondary ion mass spectra of the mixture of the tryptic peptides could reveal the aberrant peptide and predict possible substitution through the mass difference between the normal and abnormal peptide. The mass spectra of the isolated abnormal peptide generally contained sufficient fragment ions to define the position of the amino acid substitution, obviating the need for lengthy sequencing procedures. Combination of the two techniques.