Production of functional human fetal hemoglobin in Nicotiana benthamiana for development of hemoglobin-based oxygen carriers.

Hemoglobin-based oxygen carriers have long been pursued to meet clinical needs by using native hemoglobin (Hb) from human or animal blood, or recombinantly produced Hb, but the development has been impeded by safety and toxicity issues. Herewith we report the successful production of human fetal hemoglobin (HbF) in Nicotiana benthamiana through Agrobacterium tumefaciens-mediated transient expression. HbF is a heterotetrameric protein composed of two identical α- and two identical γ-subunits, held together by hydrophobic interactions, hydrogen bonds, and salt bridges. In our study, the α- and γ-subunits of HbF were fused in order to stabilize the α-subunits and facilitate balanced expression of α- and γ-subunits in N. benthamiana. Efficient extraction and purification methods enabled production of the recombinantly fused endotoxin-free HbF (rfHbF) in high quantity and quality. The transiently expressed rfHbF protein was identified by SDS-PAGE, Western blot and liquid chromatography-tandem mass spectrometry analyses. The purified rfHbF possessed structural and functional properties similar to native HbF, which were confirmed by biophysical, biochemical, and in vivo animal studies. The results demonstrate a high potential of plant expression systems in producing Hb products for use as blood substitutes.

Comparison of fast protein liquid chromatography (FPLC) with HPLC, electrophoresis & microcolumn chromatography techniques for the diagnosis of beta-thalassaemia.

BACKGROUND & OBJECTIVE: beta-thalassaemia is a genetic disorder and an important health problem around the world. Quantitative haemoglobin A(2) (HbA(2)) levels are used for the diagnosis of beta-thalassaemia. The conventional methods are high performance liquid chromatography (HPLC), electrophoresis, and microcolumn chromatography techniques. We established a fast protein liquid chromatography (FPLC) method, to measure quantitatively of HbA(2) levels, and compared its efficacy with conventional methods. METHODS: The FPLC method, using a DEAE Sepharose, Hi Trap anion-exchange column chromatography technique was set up for HbA(2) measurement. In this study, 220 blood samples were screened for haemoglobin type by FPLC technique and also using HPLC, microcolumn chromatography and electrophoresis. RESULTS: The FPLC results were highly correlated (r = 0.985, P<0.001) with those of HPLC for quantification of HbA(2) as well as cellulose acetate electrophoresis (r = 0.977) and microcolumn chromatography (r = 0.980). The FPLC method showed 100 per cent sensitivity and specificity, positive and negative predictive value for beta-thalassaemia diagnosis. In addition, the FPLC method was simple, rapid, low cost and reproducible. The HbA(2)/E range of FPLC for beta-thalassaemia was 6-10 per cent, HbE trait was 10-40 per cent, beta-thalassaemia/HbE was 40-60 per cent and homozygous HbE was more than 60 per cent. INTERPRETATION & CONCLUSION: Our findings suggested that FPLC method could be used as a cost-effective method for routine beta-thalassaemia diagnosis.

Heterogeneity in the globin chain composition of a human minor fetal hemoglobin component.

The first hemoglobin found to contain an acetyl blocking group was the minor human fetal hemoglobin, Hb FI, present as 10-15% of the total fetal hemoglobin in umbilical cord blood red cells. Acetylation occurs at the amino-terminal glycine of the gamma-globin chain. Assays for the acetyl group by two different methods gave values less than the 2 per tetramer expected for a fully acetylated hemoglobin. We have purified acetylated fetal hemoglobin FIc to homogeneity. The globin chain composition of Hb FIc has been examined by both globin chain separation on CM-cellulose and by tryptic peptide mapping by HPLC. The identities of the gamma globin chains and of the gamma T-1 peptides were confirmed by amino acid analysis. Globin chain separation profiles showed the presence of 22.3 +/- 7.0% of gamma 0 globin (of the total gamma globin) in Hb FIc. Accordingly, the tryptic peptide maps of Hb FIc tetramers also showed the presence of a similar amount of gamma 0T-1 peptide. The gamma 0T-1 peptide was not present in the maps of isolated gamma Ic globin. It is evident that column purified Hb FIc contains a certain percentage of non-acetylated gamma-globin chains, thus indicating a hybrid globin chain composition for this minor fetal hemoglobin component.

Characterization of a new fetal hemoglobin variant, Hb F Izumi A gamma 6Glu replaced by Gly, by molecular secondary ion mass spectrometry.

Molecular secondary ion mass spectrometry has characterized the structure of a new fetal hemoglobin variant, Hb F Izumi, without separation of peptides or amino acid analysis. First, the mass spectrum of a tryptic digest of the abnormal gamma globin revealed a decreased by 72 mass units in the molecular mass of peptide T-1,2, indicating the presence of a Glu leads to Gly substitution. Next, the analysis of the digest produced by the addition of staphylococcal protease, which specifically cleaves glutamyl peptide bonds, determined the site of substitution at 6th glutamic acid residue in peptide T-1,2 which contains two glutamic acid residues. Since this mass spectrometric approach provides digitalized data on peptide analysis, we call it 'digit printing'. The high sensitivity of this technique is especially promising for the analysis of molecular abnormality in various genetic disorders.

Glycosylated minor components of human fetal hemoglobin. Chromatographic separation, identification, and functional characterization.

Human adult red cell lysate contains glycosylated minor hemoglobins AIa1, AIa2, AIb, and AIc. Similar minor hemoglobins, designated FIa1, FIa2, Fib, and FIc, have been separated by a Biorex 70 column chromatographic procedure from red cell lysates of newborn children and from an adult homozygote for hereditary persistence of fetal Hb. The minor Hb components were characterized by analyzing for carbohydrate and phosphate contents, by oxygen equilibrium analysis, and by comparing the chromatographic elution profiles of naturally occurring and in vitro synthesized minor components. The results indicate that Hb FIa1, Hb FIa2, and Hb FIc have been formed by the modification of gamma chains of Hb F by reacting with fructose-1,6-P2, glucose-6-P, and glucose, respectively. Hb FIb is a glycoprotein; the mechanism of its formation is unclear. Hb FIa1 and Hb FIa2 had significantly lower oxygen affinities and n values than the other minor components and the major Hb F0. Moreover, 2,3-diphosphoglycerate did not influence the oxygenation of the minor or the major fetal Hb components. Incubations of Hb F with [14C]hexoses and subsequent chromatographic separation of hemoglobins and their globin chains confirm the previous findings that the binding of carbohydrate to Hb involves both specific and nonspecific reactions.

Isolation and characterization of human foetal alpha-globulin (alpha 1F) from foetal and hepatoma sera.

The alpha 1F present in human foetal sera and the serum from a patient with hepatocellular carcinoma was isolated by immune precipitation using rabbit anti-alpha 1F. After labelling with 125I, some physicochemical properties of alpha 1F were investigated. The molecular weights of 125I-labelled alpha 1F isolated from foetal and hepatoma sera were 61,000 and 63,000, respectively. The protein was not dissociated in 6 M guanidine after complete reduction, showing that it contains a single peptide chain.

The isolation of the gamma subunit of fetal hemoglocin (HbF) and its use in a radioimmunoassay for HbF.

A method is described for the purification, from fetal hemoglobin (HbF), of the fetal specific globin chain (gamma chain) in its native state. In the absence of alpha chain (the globin chain common to all adult human hemoglobins) gamma chain, when used as an immunogen, is able to express its unique antigenicity. Here, a specific, high titer antiserum raised against gamma chain has been used to establish a sensitive radioimmunoassay for HbF. This approach may be applicable to the measurement of other normal and abnormal hemoglobins.

An immunofluorescent procedure for detection of Hb F (gamma chain) in peripheral erythrocytes.

A direct fluorescent method for the detection of the gamma chain of Hb F in erythrocytes is described. The method is easier to interpret and more sensitive than the classic Kleihauer-Betke procedure.

Interference with glycated hemoglobin by hemoglobin F may be greater than is generally assumed.

An automated electrophoretic method to measure glycated hemoglobin (Hb A1) was compared with manual affinity methods. Good correlation between methods was found. The electrophoretic method showed good run-to-run precision, good linearity, was free from interference by the labile aldimine fraction, and required less time and considerably less consumable expense than the affinity methods. However, as previously reported, Hb F comigrating with Hb A1 caused spurious increases in glycated Hb levels as compared with the affinity methods. This effect was linearly dependent on the Hb F concentration. Using the discrepancy between concentrations of Hb A1 by electrophoresis and glycated hemoglobin by affinity methods, 330 patients were screened in two hospitals for Hb F. A 12% frequency of elevated Hb F (defined as a level that is more than 2%) was found in patients from a community-tertiary care hospital, which is significantly greater than the 1.5% frequency commonly thought to occur in the adult population at large, whereas patients from a Veterans Administration Hospital showed an elevated frequency of 2.2%. Based on this and other studies, it is concluded that the frequency of elevated Hb F in adults may very substantially among different medical centers. The authors recommend against using this method and suggest that laboratories that persist in using it should periodically assess the frequency in patients with Hb F levels greater than 2% of total hemoglobin, replacing the method if an unacceptably high frequency is found.

Identification of five embryonic hemoglobins of rat and ontogeny of their constituent globins during fetal development.

Hemoglobins of rats switch from an embryonic to an adult type during fetal development. However, very little is known about the structures and molecular species of hemoglobins occurring in the fetal life of rats. In the present study we isolated five embryonic hemoglobins, designated E1, E2, E3, E4, and E5, from the blood of rat fetuses on day 14 of gestation by ion exchange chromatography. Reverse-phase high performance liquid chromatography revealed that these hemoglobins each consist of two kinds of globins: E1(11 alpha:epsilon 1), E2(1 alpha: epsilon 1), E3(zetta: epsilon 1), E4(1 alpha: epsilon 3), and E5(zetta: epsilon 3), respectively. The complete amino acid sequences of the zetta, epsilon 1, and epsilon 3 globins were determined. The zetta globin showed characteristic features common in alpha-type embryonic globins of known species in that the N-terminus is blocked and the amino acid at position 38 is Gln. epsilon 1 and epsilon 3 are beta-type embryonic globins, sharing 73.7% amino acid homology. Interestingly, they are more similar to the corresponding mouse beta-type embryonic globins, y and z, respectively, than to each other, implying that these globins have evolved orthologously from common ancestral proteins. It was also shown that the zetta, epsilon 1, and epsilon 3 globins are almost completely replaced by the adult type alpha and beta globins in the blood of rat fetuses by day 18 of gestation.

Asymmetric hybrids between hemoglobin Alberta (alpha 2 beta 2 101 Glu replaced by Gly) and hemoglobins A, A2 or F1 in different liganded states.

Isoelectric focusing in cylindrical polyacrylamide gels has been used to demonstrate the formation of asymmetric hybrids between an abnormal hemoglobin, Hb Alberta (alpha 2 beta 2 101 Glu replaced by Gly), and Hb A (alpha 2 beta 2), Hb A2 (alpha 2 delta 2) or Hb F1 (alpha 2 gamma 2 Acetyl). There was no discernible difference in the stabilities of the three hybrids (alpha 2 beta A beta Alberta, alpha 2 delta beta Alberta and alpha 2 gamma Acetyl beta Alberta) in the oxy, carboxy or cyanmet hemoglobin forms. Two mixed liganded hybrids, (alpha beta A)oxy (alpha beta Alberta)cyanmet and (alpha beta A)cyanmet (alpha beta Alberta)oxy were also demonstrated and found to have stabilities similar to that of the Hb Alberta hybrids.

Isoelectrofocusing: a method of multiple applications for hemoglobin studies.

A microanalytical screening of hemoglobins by isoelectric focusing on acryl-amide gel columns is described. Addition of this technique to our regular analytical procedures revealed many mutants, praticularly some neutral ones which were not resolved by other conventional procedures. Extension of this technique to a quantitative scale permitted rapid isolation of some unstable mutants in an almost pure form ready for functional studies. The natural color of the separated components is often indicative of their nature and in cases like the sulfhemoglobin, Hbs M, they are of diagnostic value. The heme-losing, abnormal, unstable mutants, on the addition of external cyanhemin, take them up and change their isoelectric pH. This is an attractive visible procedure for their diagnosis. From all these results, it appears that isoelectric focusing as a single method brings more information than the other conventional procedures and hence can be considered as a semi-routine investigation for hemoglobin studies before deciding on a much longer procedure.

An HbF enrichment procedure for the HPLC analysis of gamma chains.

A rapid and inexpensive method is described for the enrichment of fetal hemoglobin (HbF) which eliminates the interference of other hemoglobins in the HPLC analysis of gamma chains when HbF is less than or equal to 20-30% of the total Hb. The enrichment procedure, which is carried out on 1 ml hemolysate, is based on the alkaline denaturation of the other Hbs followed by Zn2+ precipitation. Samples are injected into the HPLC apparatus without further treatment. The method was validated by HPLC analysis of hemolysates with high levels of HbF and mixtures prepared by diluting the high HbF hemolysates with adult hemolysates. The relative proportions of gamma chains as well as their chromatographic behavior were unaltered by the HbF enrichment procedure. The method is illustrated by the analysis of hemolysates of normal newborns and of patients with thalassemia, sickle cell diseases and aplastic anemia containing 3.4 to 100% HbF. For the four hemolysates containing greater than 20% HbF, the same quantitative and chromatographic results were obtained by direct analysis and after enrichment. Although reproducible and accurate results were obtained for the enrichment method and HPLC analysis when HbF was greater than or equal to 3%, at lower concentrations the variability of both was unacceptably high, indicating the need for additional or improved methodology for hemolysates containing very low levels of HbF.

Separation of hemoglobin variants in single human erythrocytes by capillary electrophoresis with laser-induced native fluorescence detection.

Single human red blood cells, in which the hemoglobin (Hb) molecules exist in their native, tetrameric states, were analyzed. Upon injection and lysis of a cell, the tetramers were dissociated on-column into their respective polypeptide chains, separated, and detected by laser-induced native fluorescence detection with 275-nm excitation. This technique was applied to the determination of hemoglobin variants as found in adult (normal and elevated Hb A1) and fetal erythrocytes. Normal adult cells contained 9.6% and 4.8% glycated beta- and alpha-chains, respectively. Cells with elevated Hb A1 gave 30% and 12%, respectively. The amounts of glycated Hb and total Hb in a given cell were found to be uncorrelated.

[Separation of hemoglobins F, Fac, S, C, A1c and determination of hemoglobin F using high performance liquid chromatography]. / Séparation des hémoglobines F, Fac, S, C, A1c et dosage de l'hémoglobine F par chromatographie liquide haute performance.

Separation of hemoglobins F, Fac, S, C and A1c was performed using high performance liquid chromatography with a cation exchange Polycat A column in a 15-minute assay. HbF titration results were well correlated with those of the reference alkali denaturation technique for values below 12% (r = 0.95; P < 0.001). This technique may be used as a confirmation test for neonatal screening of sickle cell disease.