Isolation and characterization of two minor fractions of alpha 1-antitrypsin by high-performance liquid chromatographic chromatofocusing

Sensitive and specific measurement of alpha1-antitrypsin activity with an elastase complex formation immunosorbent assay (ECFISA)

Functionally active alpha₁-antitrypsin (AAT) is measured predominantly with a chromogenic elastase inhibition assay, where the concentration of AAT activity inversely correlates with the levels of residual elastase. This standard assay has moderate sensitivity as it hardly allows the measurement of samples containing less than 10 µg of functionally active AAT per mL. To overcome this drawback, we developed a new assay format for the measurement of functionally active AAT, which we termed the elastase complex formation immunosorbent assay (ECFISA). The ECFISA uses plate-bound, still proteolytically active elastase, which attacks functionally active AAT under irreversible formation of a stable stochiometric 1 + 1 complex. This complex is then detected and measured by an anti-AAT peroxidase conjugate. Using three different approaches for the preparation of functionally inactive AAT - heating, oxidation, and complex formation with elastase - we confirmed beyond doubt that the ECFISA exclusively measures functionally active AAT and that these measurements are unimpaired by the presence of high concentrations of functionally inactive AAT. Studies addressing the coating procedure demonstrated that adequate and robust conditions had been defined for this essential first step of the ECFISA. Possible interference caused by the presence of important plasma proteinase inhibitors in the test samples could be excluded for the most abundant inhibitors. Even a 1.5-times molar excess of alpha₂-macroglobulin over AAT was shown to have no impact, which is not the case for a conventional chromogenic activity assay. Functional activities determined with the ECFISA and validated chromogenic elastase inhibition assay matched well with a mean absolute bias of 0.64% calculated for the 25 samples measured. The results of the bioanalytical assay validation complied with the acceptance criteria for ligand-binding assays as given by current guidelines on validation of bioanalytical methods. Overall, the data obtained demonstrated the ECFISA as an accurate, precise, selective, and very sensitive method for AAT activity measurement at low levels previously inaccessible for direct measurement.

α1Proteinase inhibitor regulates CD4+ lymphocyte levels and is rate limiting in HIV-1 disease

BACKGROUND

The regulation of adult stem cell migration through human hematopoietic tissue involves the chemokine CXCL12 (SDF-1) and its receptor CXCR4 (CD184). In addition, human leukocyte elastase (HLE) plays a key role. When HLE is located on the cell surface (HLE(CS)), it acts not as a proteinase, but as a receptor for α(1)proteinase inhibitor (α(1)PI, α(1)antitrypsin, SerpinA1). Binding of α(1)PI to HLE(CS) forms a motogenic complex. We previously demonstrated that α(1)PI deficiency attends HIV-1 disease and that α(1)PI augmentation produces increased numbers of immunocompetent circulating CD4(+) lymphocytes. Herein we investigated the mechanism underlying the α(1)PI deficiency that attends HIV-1 infection.

METHODS AND FINDINGS

Active α(1)PI in HIV-1 subjects (median 17 µM, n = 35) was significantly below normal (median 36 µM, p<0.001, n = 30). In HIV-1 uninfected subjects, CD4(+) lymphocytes were correlated with the combined factors α(1)PI, HLE(CS) (+) lymphocytes, and CXCR4(+) lymphocytes (r(2) = 0.91, p<0.001, n = 30), but not CXCL12. In contrast, in HIV-1 subjects with >220 CD4 cells/µl, CD4(+) lymphocytes were correlated solely with active α(1)PI (r(2) = 0.93, p<0.0001, n = 26). The monoclonal anti-HIV-1 gp120 antibody 3F5 present in HIV-1 patient blood is shown to bind and inactivate human α(1)PI. Chimpanzee α(1)PI differs from human α(1)PI by a single amino acid within the 3F5-binding epitope. Unlike human α(1)PI, chimpanzee α(1)PI did not bind 3F5 or become depleted following HIV-1 challenge, consistent with the normal CD4(+) lymphocyte levels and benign syndrome of HIV-1 infected chimpanzees. The presence of IgG-α(1)PI immune complexes correlated with decreased CD4(+) lymphocytes in HIV-1 subjects.

CONCLUSIONS

This report identifies an autoimmune component of HIV-1 disease that can be overcome therapeutically. Importantly, results identify an achievable vaccine modification with the novel objective to protect against AIDS as opposed to the current objective to protect against HIV-1 infection.

Ethanol dependence of alpha 1-antitrypsin C-terminal Lys truncation mediated by basic carboxypeptidases

BACKGROUND

Patients with hereditary emphysema are treated with alpha 1-antitrypsin (alpha 1-proteinase inhibitor [A1PI]) concentrates. High-resolution isoelectric focusing (IEF) analysis of A1PI shows that commercial A1PI products have different glycoisoform band patterns predominantly caused by varying degrees of C-terminal Lys truncation at position 394 from the A1PI molecule. Basic carboxypeptidases (CPs) are a group of enzymes that specifically cleave C-terminal basic amino acids (Arg or Lys) from peptides and proteins.

STUDY DESIGN AND METHODS

In this study, whether A1PI is a substrate for basic CPs was investigated. CPN and CPU, two CPs present in plasma, and CPM, a GPI-anchored membrane protein highly expressed in lung tissues, were included.

RESULTS

Basic CPs are able to mediate the C-terminal Lys truncation of A1PI although with a very low efficiency. However, presence of ethanol, for example, during Cohn fractionation, renders A1PI highly susceptible to cleavage by CP with the extent of Lys truncation depending on the ethanol concentration. This ethanol concentration dependence elegantly explains the varying amounts of des-Lys A1PI present in commercial preparations purified from different Cohn fractions.

CONCLUSIONS

The cause of C-terminal truncation of A1PI present in products used for augmentation therapy has been identified, and it has been shown that A1PI becomes a substrate for CPs, specifically CPN, because of the presence of ethanol during Cohn fractionation.

Convenient high-resolution isoelectric focusing (IEF) method for the separation of alpha1-proteinase inhibitor (A1PI) isoforms in A1PI concentrates

Currently, high-resolution separation of A1PI is done in highly specialized laboratories using gels made in-house. This paper presents a high-resolution method for the separation of A1PI concentrates and human plasma using commercially available gels. Hybrid IEF was performed with carrier ampholytes and the gels were stained with Coomassie Brilliant Blue G-250. In addition, a sensitive immunoblotting procedure is described. The IEF method allowed the reproducible and convenient determination of the IEF pattern of A1PI in concentrates including resolution of glycan-dependent isoforms and isoproteins with secondary modifications such a C-terminal Lys-truncation. Furthermore, a shift in the IEF pattern of A1PI occurring upon reduction could be detected. Finally, in combination with a sample pretreatment step, the method proved able to monitor complex A1PI isoform patterns in samples with low A1PI concentrations as present for example in bronchoalveolar lavage solutions.

Biochemical, molecular characterization, and glycoproteomic analyses of alpha(1)-proteinase inhibitor products used for replacement therapy

BACKGROUND

Isoelectric focusing (IEF) of alpha(1)-proteinase inhibitor (A1PI) shows that commercial products and plasma have different glycoisoform band patterns. Those in Aralast (Grifols Biologicals) reflect an anodal shift of glycoisoforms, which has caused concern. The protein, including glycoproteomic analyses, and structural features of A1PI products were investigated by state-of-the-art techniques.

STUDY DESIGN AND METHODS

Batches from Aralast, Prolastin (Bayer), and Zemaira (Aventis Behring LLC) were analyzed by high-resolution IEF and high-performance size-exclusion chromatography (HP-SEC). Preparative separated isoforms from IEF were further purified by chromatography and subjected to mass spectrometry for sequence analyses, peptide mapping, and glycosylation analysis. Deamidation was quantified by enzymatic isoaspartate detection. Multiple sequence alignments and structural bioinformatics analyses were performed.

RESULTS

In HP-SEC, Prolastin had the highest aggregate content at approximately 30 percent. Isoforms from all products purified by high-resolution IEF were sequenced with an amino acid coverage of more than 98 percent. Deamidation of Asn116 and Asn314 in A1PI was to found to some extent in all products and confirmed quantitatively by enzymatic analysis. There were no signs of methionine oxidation. Cys232 was found to be cysteinylated in A1PI in Prolastin and Aralast as in plasma, but not in Zemaira. All products showed truncation of the C-terminal lysine. Intact A1PI concentrates contained mainly diantennary, disialylated and smaller amounts of triantennary, trisialylated N-glycans. The percentage of fucosylation was similar in all products. Site-specific glycan analysis revealed bands M6 contained only diantennary glycans, whereas the more acidic bands M4 and M2 also carried triantennary structures. The most acidic isoforms, M2 in Prolastin and Zemaira and M0 in Aralast, additionally exhibited tetraantennary N-glycans.

CONCLUSION

Protein chemical characterization of A1PI showed that all A1PI products to some extent differ from A1PI circulating in human plasma. Bioinformatic analysis indicated that removal of C-terminal Lys394 and cysteinylation of Cys232 are unlikely to affect structure and/or function of A1PI but cysteinylation may influence interaction between A1PI and its physiologic ligands. Aralast, Prolastin, and Zemaira contain the same set of N-glycans in the same ratios as those in normal human plasma A1PI. Tri- and tetraantennary structures are responsible for the partitioning into IEF isoforms, with the migration shift of Aralast not being due to any difference in the N-glycosylation, but to the partial loss of the C-terminal lysine.

Comprehensive glyco-proteomic analysis of human alpha1-antitrypsin and its charge isoforms

Human alpha1-antitrypsin (A1PI) is a well-known glycoprotein in human plasma important for the protection of tissues from proteolytic enzymes. The three N-glycosylation sites of A1PI contain diantennary N-glycans but also triantennary and even traces of tetraantennary structures leading to the typical IEF pattern observed for A1PI. Here we present an approach to characterize A1PI isoforms from human plasma and its PTMs by LC-ESI-MS and LC-ESI-MS/MS of peptides obtained by proteolytic digestion. The single cysteine residue of A1PI formed a disulfide bridge with free cysteine. The variability of the number of antennae and hence sialic acids on glycosylation site N107, which even contained minute amounts of tetraantennary structures, emerged as a major cause for the IEF pattern of A1PI. Only negligible amounts of triantennary structures were identified attached to N70, and exclusively diantennary structures were present on site N271 in each of the isoforms analyzed. Exoglycosidase digests revealed alpha2,6-linked neuraminic acids on diantennary N-glycans, and triantennary contained additionally one single alpha2,3-neuraminic acid per N-glycan, which, together with a fucose, formed a sialyl Lewis X determinant on the beta1,4-linked N-acetylglucosamine, as shown by 2-D-HPLC of pyridylaminated asialoglycans. Fucosylation of diantennary structures was marginal and of the core alpha1,6 type.

Identification of α1-Antitrypsin Variants in Plasma with the Use of Proteomic Technology

Background: Proteomic technology permits the investigation of genetic metabolic diseases at the level of protein expression. Changes in the expression, polypeptide structure, and posttranslational modification of individual proteins can be detected in complex mixtures of proteins.

Methods: We used high-resolution two-dimensional polyacrylamide gel electrophoresis to separate isoforms of plasma proteins and detect abnormalities of mass and/or charge. We confirmed the identity of the separated proteins by in-gel digestion with proteases and N-glycanases and then analyzed the released peptides and glycans by matrix-assisted laser-desorption ionization–time-of-flight mass spectrometry.

Results: Complete characterization of the polypeptide sequences and glycosylation of α1-antitrypsin isoforms was achieved in plasma from controls and from patients with three different known α1-antitrypsin deficiencies and congenital disorder of glycosylation type Ia.

Conclusions: This study shows that proteomic techniques are a powerful and sensitive means of detecting changes in the amino acid sequence and abnormal posttranslational modifications of specific proteins in a complex biologic matrix.

Congenital disorders of glycosylation type I leads to altered processing of N-linked glycans, as well as underglycosylation

The N-linked glycans on transferrin and alpha(1)-antitrypsin from patients with congenital disorders of glycosylation type I have increased fucosylation and branching relative to normal controls. The elevated levels of monofucosylated biantennary glycans are probably due to increased alpha-(1-->6) fucosylation. The presence of bi- and trifucosylated triantennary and tetra-antennary glycans indicated that peripheral alpha-(1-->3), as well as core alpha-(1-->6), fucosylation is increased. Altered processing was observed on both the fully and underglycosylated glycoforms.

Preparation and properties of an alpha-1-protease inhibitor concentrate with high specific activity

BACKGROUND AND OBJECTIVES

Because the current demand for alpha-1-protease inhibitor (A1PI) exceeds the available supply, we aimed to develop a process for purification of A1PI from plasma which would achieve the highest possible degree of purity, specific activity and yield.

MATERIALS AND METHODS

A1PI was purified from Cohn fraction IV-1,4 using ethanol precipitation and Q-Sepharose chromatography. Ceramic hydroxyapatite chromatography was used as a final purification step. Two independent virus-inactivation procedures (chemical and vapour heating) were applied.

RESULTS

The resulting A1PI had an unprecedented high specific activity. In addition, the process led to the discovery of a new isoform of A1PI in isoelectric focusing gels.

CONCLUSION

The high specific activity of the A1PI preparation achieved with this process should allow a reduction of the A1PI total protein load necessary to achieve clinically relevant effects.

Analyzing glycoproteins separated by two-dimensional gel electrophoresis

Two-dimensional (2-D) electrophoresis is the preferred method for separating the glycoforms of proteins. The isoforms usually present as 'trains' of spots in the first dimension and may also differ in molecular weight. The primary goal for analyzing the carbohydrate content of glycoprotein spots is to understand the 'rules' which govern the migration of glycoproteins in 2-D electrophoresis. These rules can then be used to produce predictive vectors to interpret changes in glycosylation patterns. Techniques for the analysis of oligosaccharides released from glycoproteins which have been electroblotted to PVDF membrane after one-dimensional (1-D) and 2-D preparative gel electrophoresis are described. The oligosaccharides are removed enzymatically (PNGase F of N-linked oligosaccharides) or chemically (beta-elimination of O-linked oligosaccharides) and separated by high performance anion exchange chromatography (HPAEC-PAD) and identified by electrospray ionization mass spectrometry (ESI-MS) or analyzed directly by ESI-MS. After enzymic removal of the N-linked oligosaccharides the protein spots can be further analyzed by Edman sequence tagging for identification and quantitation of the protein and by acid hydrolysis for monosaccharide analysis of the O-linked oligosaccharides. These approaches have been proved on 1-D PAGE electroblotted bovine fetuin and human glycophorin A and then used to analyze two abundant proteins which separate as glycoforms on 2-D PAGE preparative narrow range (pH 4.5-5.5) blots of human plasma: alpha2-HS glycoprotein (human fetuin) and alpha1-antitrypsin (alpha1-protease inhibitor). It is apparent that both the macroheterogeneity (site occupation) and microheterogeneity (diversity of structures) of the glycosylation contribute to the separation of protein isoforms in 2-D PAGE.

Effects of mutations in the hinge region of serpins

An expression system for alpha 1-antitrypsin in Escherichia coli was developed using a T7 RNA polymerase promoter. Addition of rifampicin to inhibit the E. coli RNA polymerase after induction of the T7 RNA polymerase gene resulted in about 30% of newly synthesized protein being alpha 1-antitrypsin. This expression system was then used to examine the effect of mutations in the hinge region of alpha 1-antitrypsin on its activity. The mutations were based on ones in antithrombin III that had previously been shown to have adverse effects on activity. Mutation of Ala347 to threonine in alpha 1-antitrypsin did not affect the kinetic behavior of the protein with trypsin or human leukocyte elastase. In contrast, mutation of Gly349 to proline converted the majority of the protein into a substrate for both proteinases. The small fraction of this mutant that was active, however, had kinetic parameters that were indistinguishable from wild-type alpha 1-antitrypsin. Cleavage within the reactive-site loop of wild-type alpha 1-antitrypsin causes a conformational change in the molecules (the S-to-R transition) and results in a marked increase in heat stability. This increase in heat stability was also seen upon cleavage within the reactive-site loops of both of the alpha 1-antitrypsin mutants. The results are discussed in terms of a kinetic mechanism for serpin-proteinase interactions, in which after the formation of an initial complex the serpin partitions between the formation of a stable complex and a cleavage reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycan microheterogeneity of alpha 1-antitrypsin in serum and meconium from normal and cystic fibrosis patients by crossed immunoaffinoelectrophoresis with different lectins (Con A, LCA, WGA)

In order to test whether abnormalities of glycosylation occur in cystic fibrosis (CF), the glycan microheterogeneity of alpha 1-antitrypsin (alpha 1-AT) was studied in serum and meconium from normal individuals and patients with cystic fibrosis, by crossed immunoaffinoelectrophoresis (CIAE) using free Concanavalin A (Con A), Lens culinaris lectin (LCA) and wheat germ agglutinin (WGA). Three main results emerged from this study: (1) modification of glycosylation in serum alpha 1-AT from patients with cystic fibrosis were only significant with free Con A and WGA; this probably results from a reduced synthesis of the bi-antennary side-chains or by their increased catabolism. (2) Differences in isoforms found in alpha 1-AT from normal individuals and patients with CF using free Con A, LCA, were more pronounced in the meconium than in the serum; this may provide a useful test in diagnosis of cystic fibrosis. (3) There was parallelism between the behaviour of alpha 1-AT in serum and meconium from patients with CF using LCA, Con A; this may be explained by different types or levels of disfunction affecting a glycosylation mechanism.

Reliable phenotyping of alpha-1-antitrypsin by hybrid isoelectric focusing in an ultranarrow immobilized pH gradient

Genetically determined phenotypes of the highly polymorphic human alpha 1-antitrypsin were examined by hybrid isoelectric focusing in a narrow immobilized pH gradient. The chosen pH range from 4.45 to 4.75 was useful for identification and classification of the common PI M subtypes and a number of PI variants in the microheterogeneous regions of m6, m7, and m8. A high degree of resolution and an improved sharpness of PI bands was achieved with this excellent technique. It allowed the distinction of a new PI M variant, which has been designated M8, or Mingolstadt, according to the PI nomenclature. The pI difference of this mutant to the slightly cathodically located subtype M3 is approximately 0.001 pH unit. In addition, some common as well as rare phenotypes are presented.

The carbohydrate deficient glycoprotein syndrome in three Japanese children

We describe 3 children (from two families) with a multisystemic disorder characterized by mental retardation, nonprogressive ataxia, polyneuropathy, hepatopathy during infancy and growth retardation. Due to the clinical similarities to a recently recognized disorder associated with carbohydrate-deficient transferrin, we examined serum transferrin by means of isoelectric focusing, and found increases in disialo transferrin and asialotransferrin. Removal of sialic acid with neuraminidase revealed the same transferrin phenotypes as in their parents. Similarly, carbohydrate-deficient fractions of serum alpha 1-antitrypsin were also detected. Therefore, the diagnosis was made of the recently identified carbohydrate-deficient glycoprotein syndrome. This is a genetic disorder with distinctive clinical features and multiple carbohydrate-deficient glycoproteins. These seem to be the first reported Japanese patients with this syndrome.

Characterization of a 54 kDa, alpha 1-antitrypsin-like protein isolated from ascitic fluid of an endometrial cancer patient

A protein factor which stimulated [3H]thymidine uptake into free hepatocytes prepared from normal mouse liver was detected in the ascitic fluid of gynecological cancer patients. The factor was subsequently further purified from the ascitic fluid of an endometrial cancer patient by DEAE-Sephacel, Sephadex G-150 and Phenyl-Sepharose CL-4B column chromatographies, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a single protein band of 54,000 Da, designated tentatively as 54K ascitic protein (54K-AP). 54K-AP was similar to human alpha 1-antitrypsin (alpha 1-AT) in terms of SDS-PAGE and immunological behavior, but was slightly different in terms of amino acid sequence and isoelectric point. Although 54K-AP inhibited the activities of bovine trypsin and alpha-chymotrypsin as did human alpha 1-AT, 54K-AP inhibited the plasminogen activator released from human endometrial cancer Ishikawa cells more efficiently than alpha 1-AT. Because, in contrast to normal serum, the serum from the endometrial cancer patients stimulated [3H]thymidine uptake into hepatocytes, the possibility arises that 54K-AP could be produced by the cancer host as a defence mechanism against the cancer.

Purification and biochemical characterization of recombinant alpha 1-antitrypsin variants expressed in Escherichia coli

Site-directed variants of alpha 1-antitrypsin (alpha 1AT) expressed in a recombinant strain of Escherichia coli have been isolated with an overall process yield of 50% following tangential flow ultrafiltration, anion-exchange, immobilized metal affinity, and hydrophobic interaction chromatography. The primary structure of the purified variants including the integrity of the N- and C-termini has been verified by electrospray mass spectrometry of the intact molecules (44 kDa) for two of the variants (alpha 1AT Leu-358 and alpha 1AT Ala-357, Arg-358). Complementary classical peptide mapping and automated amino acid sequencing have verified 75% of the primary sequence of alpha 1AT Ala-357, Arg-358. Isoelectric focusing in an immobilized pH gradient revealed some microheterogeneity which proved to be reproducible from one purification batch to another. The isolated variants of alpha 1AT did not show any signs of proteolytic degradation during the purification process and proved to be fully active against their target proteases. The described process also allowed the complete removal of endotoxins from the preparations, opening the possibility to evaluate these novel protease inhibitors for their in vivo efficacy in different animal models of human disease.

Mammalian alpha 1-antitrypsins: comparative biochemistry and genetics of the major plasma serpin

1. Human alpha 1-antitrypsin (alpha 1 AT) has been extensively characterized and reviewed. It is the archetypal member of the superfamily of serine proteinase inhibitors, the serpins. As human alpha 1-antitrypsin exhibits a relatively high concentration in plasma and is usually the highest concentration serpin, it can be referred to as the major plasma serpin. 2. alpha 1-Antitrypsin from species other than man has been characterized for two major reasons: (1) for use in a model animal system to assist with the study of the human alpha 1 AT deficiency disease; and (2) to find polymorphism for use in gene mapping and linkage studies or for parentage analysis. 3. The diverse range of reasons for studying alpha 1AT has yielded a vast array of literature that is often not well cross-referenced. 4. The characteristic features of alpha 1AT in all species examined to date will be presented with a view to examining which features are important structurally and functionally from an evolutionary perspective. 5. In mouse, horse, rabbit and guinea pig, multigene families which appear to have arisen from alpha 1AT have been found. The functional and evolutionary implications of these paralogous genes will also be discussed.

Role of sialic acid residues in crossed immuno-affinoelectrophoresis of alpha 1-proteinase inhibitor

We have investigated the importance of the degree of sialylation when an acute phase glycoprotein, alpha 1-proteinase inhibitor (alpha 1-Pi), was analysed both by affinity chromatography on concanavalin A (Con A)-Sepharose and by crossed immuno-affinoelectrophoresis (CIAE) using Con A in the first dimension. Human alpha 1-Pi was isolated by immunosorption chromatography and then more or less desialylated. On Con A-Sepharose chromatography no significant difference was observed in the percentage of the two fractions (retained or not retained) whatever the degree of desialylation. In contrast by CIAE this degree was largely involved in the separation of the different isoforms obtained in the first dimension.

The microheterogeneity of desialylated alpha 1-antichymotrypsin: the occurrence of two amino-terminal isoforms, one lacking a His-Pro dipeptide

ACT (alpha 1-antichymotrypsin), a serine antiproteinase with specificity against neutrophil cathepsin G, is homologous with alpha 1-antitrypsin, plasminogen activator inhibitor and angiotensinogen, all with known amino-terminal microheterogeneity. Here we report that the two predominant isoforms of desialylated ACT obtained on isoelectric focusing correspond to a microheterogeneity at the amino terminus of ACT: one isoform (His-Pro-Asn-Ser-Pro-) and a two residues shorter isoform (Asn-Ser-Pro-). The relative occurrence of the two isoforms was comparable both in normal plasma, acute-phase plasma and plasma from subjects with heterozygous familial ACT deficiency. When desialylated ACT, isolated by affinity chromatography from ACT-deficient, normal or acute-phase plasma, was compared with regard to mass and charge microheterogeneity, we found no significant differences in either respect. Nor was the isoform pattern of desialylated plasma from patients with rheumatoid arthritis different. Although the occurrence of heterozygous familial ACT deficiency implies genotypic variation, isolated ACT from patients with the trait was not found to exhibit any phenotypic variation detectable by standard electrophoretic methods.

Changes in serum level and affinity for concanavalin A of human alpha 1-proteinase inhibitor in severe burn patients: relationship to natural killer cell activity

In serum from five patients with severe burns, alpha 1-proteinase inhibitor (alpha 1-PI) was analyzed and then isolated by immunosorption chromatography. By Con A-Sepharose chromatography alpha 1-PI was separated into two types of fractions: the first containing the Con A-non-reactive isoforms and the second containing the Con A-reactive isoforms. The increase of alpha 1-PI serum level in burn patients is associated on the fifth day after the burn with a significant shift toward species enriched in bi-antennary oligosaccharides (Con A-reactive isoforms). This latter change passed very quickly and ten days after the burn, whereas the alpha 1-PI serum level was still high, the difference in proportions of Con A-reactive and non-reactive isoforms was not statistically significant. With respect to the difference in oligosaccharide structure, it appeared that the glycan moiety was involved in the inhibitory effect on natural killer cell activity. At the same concentration, purified alpha 1-PI and retained alpha 1-PI isoforms had an equal effect, whereas the non-retained alpha 1-PI isoforms were more efficient (P less than or equal to 0.01). Purified alpha 1-PI and its isoforms inhibited the natural killer cell activity in a dose-dependent manner.

Molecular basis of alpha-1-antitrypsin deficiency

Alpha-1-antitrypsin (A1AT) deficiency is an autosomal hereditary disorder associated with a major reduction in serum A1AT levels. Clinically, A1AT deficiency is associated with emphysema in adults and, less commonly, liver disease in neonates. A1AT is a 52-kDa, 394-amino acid, single-chain glycoprotein normally present in serum at 150 to 350 mg/dl. The A1AT gene, composed of seven exons dispersed over 12 kb of chromosomal segment 14q31-32.3, is expressed in hepatocytes and mononuclear phagocytes. The A1AT protein, a member of the class of protease inhibitor proteins known as serpins (serine protease inhibitors), is a globular molecule composed of nine alpha-helices and three beta-pleated sheets. The major function of A1AT is to inhibit neutrophil elastase; A1AT does so through an active site centered around Met358 contained within an external stressed loop on the surface of the molecule. A1AT is a highly pleomorphic protein with greater than 75 variants determined at the protein and/or gene level. These variants can be categorized into four groups according to their serum A1AT level and function: normal, deficient, dysfunctional, and absent. There are two important salt bridges within the A1AT molecule (Glu342-Lys290; Glu263-Lys387); a mutation in the A1AT gene causing disruption of either salt bridge causes distinct molecular pathology resulting in reduced serum A1AT levels. Clinically relevant variants can be distinguished by a combination of isoelectric focusing of serum, restriction fragment length analysis of genomic DNA, oligonucleotide probes, and direct sequencing of the variant A1AT genes.

The use of dye-ligand affinity chromatography for the purification of non-enzymatic human plasma proteins

Literature data are analysed in this review on the use of immobilized triazine dyes for the characterization, isolation and purification of non-enzymatic human plasma proteins in both conventional and high-pressure liquid chromatography systems. Attention is focused on the mode of interaction between the dyes and these proteins, as well as on the advantages over previously reported techniques. Future developments are discussed.

The amino acid substitutions of human alpha 1-antitrypsin M3, X and Z

alpha 1-Antitrypsin has been isolated from individuals with inherited genetic variants M3, X and Z. A fragmentation and peptide mapping system is described which together with amino acid and sequence analyses revealed the substitutions in M3 at 376 of Glu to Asp, in X at 204 of Glu to Lys and in the physiologically innocent Z a mutation at 213 of Val to Ala. The latter represents a second amino acid substitution in the Z protein.

Purification of human alpha 1-beta glycoprotein and study of its microheterogeneity and molecular variants

Alpha 1-beta glycoprotein (A1B) was purified to homogeneity from human plasma using a three-step procedure involving pseudo-ligand affinity chromatography on immobilized Cibacron Blue 3-GA, gel filtration chromatography on Sephadex G-200 and ion-exchange chromatography on DEAE Affigel Blue. The overall yield of the combined techniques was 31%. The major advantages of this technique include its conveniency, and the fact that no apparent alteration of the purified protein occurred as judged by the absence of modification of its physicochemical parameters. A1B appears to be present in normal plasma as a major form of Mr 70,000 daltons with extensive charge heterogeneity, together with minor components of higher Mr.

Characterization of the M1(Ala213) type of alpha 1-antitrypsin, a newly recognized, common "normal" alpha 1-antitrypsin haplotype

alpha 1-Antitrypsin (alpha 1AT) is a highly pleomorphic 52-kDa serum glycoprotein that functions as the major inhibitor of neutrophil elastase. Of these, the most common normal alpha 1AT haplotypes identified by isoelectric focusing (IEF) of serum are those of the M family, including M1, M2, and M3. In the course of studying the alpha 1AT type Z gene, we identified a restriction endonuclease BstEII polymorphism in the M1 gene that predicted the existence of a previously unidentified, but relatively common, haplotype of M, referred to as M1(Ala213) [Nukiwa, T., Satoh, K., Brantly, M. L., Ogushi, F., Fells, G. A., Courtney, M., & Crystal, R. G. (1986) J. Biol. Chem. 261, 15989-15994]. In this study we have cloned both alpha 1AT genes from an individual heterozygous for the M1(Ala213) and M1(Val213) haplotypes. Sequencing of the coding exons of both demonstrated that they are identical except for the Ala-Val difference at residue 213. The codominant transmission of the M1(Ala213) gene was demonstrated in a family study. Evaluation of 39 genomic samples of Caucasians with the IEF haplotype M1 demonstrated haplotype frequencies of 68% for M1(Val213) and 32% for M1(Ala213). alpha 1AT serum levels of individuals inheriting the M1(Ala213) gene in a homozygous fashion were in the same range as those for homozygous M1(Val213) as was the rate of association of the M1(Ala213) protein with neutrophil elastase.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography of complex protein mixtures

This review has shown that a variety of chromatographic techniques are available for fractionating proteins. Fortunately, high-quality columns of every type described in this review are commercially available. Most water-soluble proteins may be eluted from size-exclusion, hydrophobic-interaction, ion-exchange, metal chelate, and bioaffinity columns with ease. When this is the case, high recovery and retention of biological activity are the norm. The exception is reversed-phase chromatography where the organic solvents and acids used in polypeptide elution denature many proteins. When problems do occur, they are generally the result of unique structural features of the protein. Very hydrophobic proteins have presented the biggest problem in that they are difficult to solubilize, particularly with retention of biological activity. It has been found that zwitterionic and non-ionic detergents are the most suitable solubilizing agents, but urea has also been used in cases where hydrophobic interacts are not as strong. Unfortunately, there is still an element of trial-and-error in selecting the most suitable solubilizing agent. Heterogeneous glycosylation of proteins also presents a problem. Both neutral and charged monosaccharides can be incorporated into proteins through multiple steps at several sites. Thus, there is the potential in a sample for a large number of glycoprotein species which have the same polypeptide backbone and differing amounts of oligosaccharide. A problem arises when size-exclusion, ion-exchange, hydrophobic-interaction, reversed-phase and bioaffinity systems begin to discriminate between these very similar glycoprotein species. Chromatographic peaks can become very broad, due to incomplete fractionation, and the polypeptide chain of interest can be associated with multiple peaks. The separation of glycoproteins requires much more study before logical procedures can be suggested for column selection and operation. Aggregated species are another class of proteins which present occasional problems. Multimeric proteins are adsorbed to sorbents by a series of forces, among which are hydrogen bonding, hydrophobic interactions, and electrostatic forces. These forces are also responsible for the maintenance of quaternary structure in proteins. When the same forces dominate both retention of protein structure and adsorption at the sorbent surface, the quaternary structure of the protein can be disrupted during elution. Very basic proteins also present a problem in some cases. Columns with residual negative charges, such as a silica-based reversed-phase column, adsorb anionic species so strongly that they are difficult to elute.(ABSTRACT TRUNCATED AT 400 WORDS)

Modification of the isoinhibitors of human serum alpha 1-proteinase inhibitor (alpha 1-antitrypsin) by pancreatic proteases

Due to the action of a serum protease, the two most cathodal isoinhibitors of the alpha 1-proteinase inhibitor (alpha 1-PI) are cleaved at the Gly5-Asp6 bond and lack two negative charges. In spite of this, these can bind trypsin and chymotrypsin, showing that the N-terminal pentapeptide is not indispensable for inhibition function. Pancreatic proteases also cleave a bond near the N-terminus in alpha 1-PI, resulting in a loss of two negative charges and a corresponding cathodal shift in the electrofocusing behavior of the isoinhibitors. Trypsin cleaves isoinhibitors near the N-terminus at a large inhibitor excess and unless an additional cleavage takes place, at least two of the new isoinhibitors remain active. An additional cleavage(s), most likely at a distance of 30-40 residues from the C-terminus results in a corresponding decrease of the molecular mass and a loss of inhibition function. Although the C-terminal cleavage peptide does separate from the protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it remains associated with it under conditions of polyacrylamide gel isoelectric focusing. Chymotrypsin also cleaved alpha 1-PI near the N-terminus but this could be observed only at protease excess and the modified isoinhibitors did not form complexes with chymotrypsin. The molecular polymorphism of alpha 1-PI is partly explained by the absence of the N-terminal pentapeptide from some of the isoinhibitors.