alpha-2-HS-glycoprotein Research Articles

Tissue transglutaminase and its substrates in bone.

Tissue transglutaminase (tTG) is an intra- and extracellular, protein-cross-linking enzyme that has been implicated in apoptosis, matrix stabilization, and cell attachment in a variety of tissues. This study provides in vivo evidence in bone of TG activity, its tissue localization, and identification of its substrates. In microplate- and blotting-based activity assays using biotinylated primary amine as a probe, we show TG activity in protein extracts from the mineralized compartment of intramembranous rat bone. Avidin affinity purification of bone extract labeled with biotinylated primary amine in the presence of tTG, in conjunction with Western blotting, permitted identification of three major noncollagenous TG substrates in bone: osteopontin (OPN), bone sialoprotein (BSP), and alpha2 HS-glycoprotein (AHSG), of which the latter two are novel substrates. Cross-linking and labeling of purified proteins confirmed their ability to serve as TG substrates, because they readily incorporated biotinylated primary amine and formed large protein aggregates in the presence of tTG. All three proteins were also identified in the high molecular weight complexes extractable from the mineralized compartment of bone. Two-dimensional (2D) gel electrophoretic analysis combined with Western blotting indicated that the proteins are not cross-linked to each other, but form distinct homotypic polymers. In the extracellular matrix of bone, tTG and isopeptide bonds were localized by immunohistochemistry in the osteoid and in the pericellular matrix surrounding osteocytes. At the cellular level, osteoblasts and osteocytes were immunostained for tTG. Collectively, these data suggest a role for tTG and its covalently cross-linked substrates in cell adhesion and possibly also in bone matrix maturation and calcification.

Interactions of α2-HS-glycoprotein (fetuin) with MMP-3 and murine squamous cell carcinoma cells

Alpha2-HS glycoprotein (fetuin) is a major plasma glycoprotein predominantly synthesized by the liver. We have previously demonstrated that human fetuin produced by hepatocellular carcinoma cells can activate the matrix metalloproteinase MMP-9 (gelatinase-B). Stromelysin-1 (MMP-3) is over-expressed in murine skin tumors and is associated with a metastatic cell phenotype. We hypothesize that fetuin plays a role in tumor progression of cell types which by themselves do not have the ability to express fetuin. Immunohistochemical staining revealed that fetuin surrounds the tumor cells in murine squamous cell carcinoma tumor specimens, similar to the expression pattern previously seen for MMP-3. The physical association of fetuin and MMP-3 was demonstrated by immunoprecipitation of radiolabeled fetuin by antibodies to MMP-3. Fetuin facilitates the conversion of pro-MMP-3 to its active form, although this effect is indirect. The association of iodinated fetuin to the cell surface of intact cultured cells derived from a murine tumor with squamous (B9) and spindle (A5) morphologies was determined by binding experiments and Scatchard analysis. Fetuin binds with Bmax values in the range of 1.26-2.1 (mean = 1.7) fmol/1 x 10(5) cells for A5 cells, and 1.5-1.7 (mean = 1.6) fmol/1 x 10(5) cells for B9 cells. The mean KD was 0.46+/-0.19 nmol for both A5 and B9 cells. Our data therefore are consistent with the model that fetuin binds to the cell surface of tumor cells and acts to localize and anchor other molecules important during tumor progression to the plasma membrane.

Catalogue of soluble proteins in the human vitreous humor: comparison between diabetic retinopathy and macular hole

Two-dimensional gel electrophoresis and mass spectrometry were used to make a catalogue of soluble proteins in the human vitreous humor (VH). Fifty-one different proteins were identified on silver-stained two-dimensional (2D) gel patterns with VH proteins obtained from diabetic retinopathy and macular hole. Thirty of these have not been listed in the reported 2D profiles of plasma. Immunoglobulin (Ig), α1-antitrypsin, α2-HS glycoprotein,and complement C 4 fragment showed stronger spots in VH with diabetic retinopathy patient samples than those with macular hole. Pigment epithelium-derived factor, a potent inhibitor of angiogenesis in the cornea and vitreous, was clearly detected in VH with diabetes. It is impressive that the inhibitor increases in the vitreous with proliferative angiogenesis.

Phosphorylation of human plasma α2-Heremans–Schmid glycoprotein (human fetuin) in vivo

A fraction of α2-Heremans–Schmid (α2-HS) glycoprotein (human fetuin) isolated from plasma was phosphorylated at serine-120 and serine-312 as shown by MS and peptide fragment sequencing after tryptic digestion. Serine-312-containing peptides were phosphorylated to 77% as determined from relative peak heights in the mass spectrum, which together with the phosphorylation of serine-120 implies a molar degree of phosphorylation of at least 1. Approximately 20% of the circulating fetuin plasma pool was phosphorylated to approx. 1mol of phosphate/mol of protein. The remainder did not contain phosphate, resulting in an average phosphorylation degree for the protein in plasma of approx. 0.2 mol/mol. The isolated α2-HS glycoprotein was a heterodimer in which the entire C-terminal part of the connecting peptide including threonine-321 was present, but traces of C-terminally trimmed connecting peptide fragments were also found. The short B-chain was O-glycosylated to approx. 40%, whereas the N-glycosylation of asparagine-138 and asparagine-158 seemed to be 100%. This finding, for the first time, that circulating human plasma fetuin is partly phosphorylated, implies that the effects of phosphorylated α2-HS glycoprotein on insulin signal transduction seen in different cell systems could be relevant to its physiological function in vivo.

Phosphorylation of human plasma α2-Heremans‒Schmid glycoprotein (human fetuin) in vivo

A fraction of alpha2-Heremans-Schmid (alpha2-HS) glycoprotein (human fetuin) isolated from plasma was phosphorylated at serine-120 and serine-312 as shown by MS and peptide fragment sequencing after tryptic digestion. Serine-312-containing peptides were phosphorylated to 77% as determined from relative peak heights in the mass spectrum, which together with the phosphorylation of serine-120 implies a molar degree of phosphorylation of at least 1. Approximately 20% of the circulating fetuin plasma pool was phosphorylated to approx. 1 mol of phosphate/mol of protein. The remainder did not contain phosphate, resulting in an average phosphorylation degree for the protein in plasma of approx. 0.2 mol/mol. The isolated alpha2-HS glycoprotein was a heterodimer in which the entire C-terminal part of the connecting peptide including threonine-321 was present, but traces of C-terminally trimmed connecting peptide fragments were also found. The short B-chain was O-glycosylated to approx. 40%, whereas the N-glycosylation of asparagine-138 and asparagine-158 seemed to be 100%. This finding, for the first time, that circulating human plasma fetuin is partly phosphorylated, implies that the effects of phosphorylated alpha2-HS glycoprotein on insulin signal transduction seen in different cell systems could be relevant to its physiological function in vivo.

THE APPLICATION OF ARTOCARPUS INTEGER SEED LECTIN-M IN THE DETECTION AND ISOLATION OF SELECTIVE HUMAN SERUM ACUTE-PHASE PROTEINS AND IMMUNOGLOBULINS

Champedak (Artocarpus integer) lectin-M is a lectin with high specificity and affinity for the core-mannosyl residues of the N-linked oligosaccharides of glycoproteins. We have studied the interaction of the champedak seed lectin with human serum glycoproteins that were resolved by 2-dimensional (2-D) gel electrophoresis. The lectin demonstrated strong interaction with haptoglobin β chain, orosomucoid, α1-antitrypsin, α2-HS glycoprotein, transferrin, hemopexin, α1B-glycoprotein, and the heavy chains of IgA, IgM and IgG of the human serum. With exceptions of the heavy chains of the immunoglobulins and α1B-glycoprotein, all the other lectin-M-probed glycopeptides are acute-phase proteins. The use of champedak lectin-M to probe for serum glycoproteins that were separated in a 2-D gel electrophoresis and Western blotting technique may be conveniently applied to analyse the acute-phase and humoral immune responses simultaneously. Subjecting human serum to immobilised-lectin-M affinity chromatography was able to isolate intact haptoglobin, α1-antitrypsin, α1B-glycoprotein, hemopexin and IgA.

Altered phosphorylation of rat dentine phosphoproteins by fluoride in vivo.

Dentine phosphoproteins have been proposed to have an important role in mineralization. This study focused on the influence of fluoride on the biochemical composition of dentine phosphoproteins and attempts to relate changes to the altered mineralization witnessed during fluorosis. Wistar rats were rendered fluorotic by the administration of 20 ppm sodium fluoride in their drinking water ad libitum, a nonfluorotic group received double-distilled, deionized water only. After 17 weeks, the teeth showed signs of fluorosis. The incisors were removed, split longitudinally, and the pulps were removed. Teeth were powdered and demineralized in 10% EDTA with protease inhibitors, after which the organic matrix was extracted with 4 M guanidinium chloride. Phosphoproteins were selectively precipitated from the soluble extract by the addition of 1.0 M calcium chloride and further purified by anion exchange chromatography. SDS-PAGE revealed two protein bands with molecular weights of 130 kDa and 66 kDa in the nonfluorotic fraction and 116 kDa and 66 kDa in the fluorotic fraction. Western blotting analysis identified the 66 kDa band as alpha2-HS glycoprotein which co-precipitated with phosphoproteins. Electroelution of the protein bands was performed with subsequent biochemical analyses. Phosphate content was determined for each protein band and was detectable in the 116 kDa and 130 kDa bands from the fluorotic and nonfluorotic samples, respectively, with a decreased level noted in the 116 kDa band. The presence of phosphate and the amino acid analysis of these bands suggested their identity to be dentine phosphoproteins. No changes in the ratio of amino acids was detected in fluorotic samples. The fluoride-induced alterations to the biochemical structure of dentine phosphoproteins would appear to influence the phosphorylation of these macromolecules only, possibly affecting posttranslational events. Such alterations may play a role in disrupting the patterns of mineralization seen during fluorosis.

Cytokine regulation of the acute‐phase protein levels in multiple myeloma

Interleukin (IL) 6 has an important role in the regulation of acute-phase proteins (APPs) during an acute-phase response. We studied IL-6 and other cytokines to determine if they regulate serum APP levels in the same way under the condition of the aberrant, long-lasting 'acute-phase response' that occurs in patients with chronic inflammation and cancer. Serum levels of nine positive APPs [CRP, SAA, C1-INH, Bf, C5, C8, C9, alpha 1-acidic glycoprotein (AGP) and haptoglobin] and two negative APPs [transferrin and alpha 2-HS glycoprotein (AHSG)] were measured using immunochemical methods in 59 multiple myeloma patients and in 72 healthy control subjects. Serum IL-6 and tumour necrosis factor (TNF) alpha levels were determined by bioassays. IL-6 was negatively correlated with five out of nine (C1-INH, C8, C9, AGP and haptoglobin) positive APPs but positively correlated with C-reactive protein (CRP). When patients with high and low IL-6 serum concentration were compared, CRP levels were higher, AGP and haptoglobin levels were lower in the high- than in the low-L-6 group, whereas no significant difference between the two groups was found in levels of the other positive and negative APPs. TNF-alpha levels were negatively correlated with transferrin and AHSG levels. No difference in the levels of positive APPs was observed between patients with low and high TNF-alpha serum concentration. By contrast, levels of both transferrin and AHSG were significantly lower in the high- than in the low-TNF-alpha group. These findings indicate that, except for regulation of the negative APPs by TNF-alpha, the mechanism of APP regulation is different under the conditions of the short-term and the chronic, long-lasting 'acute-phase reaction'.

Genetic variation in alpha 2HS-glycoprotein is related to calcaneal broadband ultrasound attenuation in older women.

Calcaneal broadband ultrasound attenuation (BUA) is an independent predictor of hip and vertebral fractures. BUA is under genetic control, but the specific genes contributing to BUA are not well defined. We examined the relationship between genetic variation in alpha2HS-glycoprotein (AHSG), an abundant noncollagenous protein of bone matrix, and calcaneal BUA. Genetic polymorphism in AHSG was determined in 222 Caucasian women (age 66-92) enrolled in the Pittsburgh Study of Osteoporotic Fractures clinical center by isoelectric focusing of serum samples. Calcaneal BUA and bone mineral density (BMD) were measured on the same foot with a Walker Sonix UBA 575(+) and single X-ray absorptiometry. Hip and spine BMD were determined with a Hologic QDR-1000 densitometer using dual-energy X-ray absorptiometry. AHSG polymorphism was not significantly related to hip, lumbar spine, or calcaneal BMD. Compared with the homozygous AHSG*2 women, calcaneal BUA was 13% lower in heterozygous (P < 0.05) and 16% lower in homozygous AHSG*1 women (P < 0.05). This relationship persisted after controlling for age, weight, height, walks for exercise, and calcaneal BMD. Current and self-reported height were also lowest in homozygous AHSG*1 women, intermediate in heterozygous women, and highest among homozygous AHSG*2 subjects. These results suggest that the AHSG polymorphism may contribute to the genetic influence on calcaneal BUA and stature.

Solid-phase synthesis of the B-chain of human α2HS glycoprotein

The B-chain of human α2HS glycoprotein 1, a heptacosapeptide carrying a trisaccharide (sialyl T) side chain, was synthesized. Prior to the Fmoc-based solid-phase synthesis of the glycopeptide, the benzyl-protected glycosyl serine building block 6 was prepared via β-stereoselective glycosylation of the 2-azido-2-deoxygalactosyl serine 11 with the sialyl galactosyl trichloroacetimidate 9. An automated peptide synthesizer was efficiently used for the elongation of the entire peptide chain except for the coupling with 6. The synthesized glycopeptide was cleaved from the resin by the TFA method. The resultant mixture of the benzylated glycopeptides was treated with TMSOTf–thioanisole in TFA and then with aq NaHCO 3 and 1,4-dithiothreitol to give 1.

Changes with age of the rat fetuin concentration in serum and its mRNA expression.

Rat fetuin, a counterpart of human alpha2-HS glycoprotein and bovine fetuin, shows strong intermolecular binding and association with other serum proteins. Therefore, to measure its concentration in rat serum, we pretreated serum samples with 1% SDS plus 5% (ca. 0.7 M) 2-mercaptoethanol at 100 degrees C for 3 min, and then subjected them to SDS-PAGE under reducing conditions followed by Western blotting. We found that the fetuin concentrations in normal rat serum determined by Western blotting were 2.5-4.5 mg/ml. These concentrations were three orders of magnitude higher than the previously reported concentrations. We also tried to measure the fetuin concentration in rat serum by means of an enzyme-linked immunosorbent assay after treatment of the samples with 0.1% sodium dodecyl sulfate (SDS) plus 10 mM 2-mercaptoethylamine at 100 degrees C for 3 min, but it gave a value of about 1/4 of that on Western blotting. Rat fetuin is expressed mainly in the liver, with a peak 2-4 weeks after birth, as determined by Northern blot analysis. The fetuin mRNA level in the liver changes almost in parallel with its serum concentration. The tibia also expresses fetuin, but much less than the liver.

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.

Structural and functional analysis of the 5′-transcription control region for the human α2-HS glycoprotein gene

The human alpha2-HS glycoprotein (A2HS) and rat phosphoprotein of Mr 63000 (pp63) are homologous plasma proteins and members of the fetuin superfamily. A2HS is involved in important functions such as inhibition of the tyrosine kinase activity of the insulin receptor, regulation of calcium metabolism and osteogenesis as well as protease inhibitory activity. We report an analysis of the 5′ transcription control region (4 kb) of the A2HS gene. Its most proximal 300 nt display a very potent transcriptional activity. The latter is likely accounted for by C/EBP and NF1 binding sites that are conserved from the human A2HS gene to the rat pp63 gene. In contrast, these human and rat genes appear to largely diverge beyond their proximal promoter.

Analysis of changes in acute-phase plasma proteins in an acute inflammatory response and in rheumatoid arthritis using two-dimensional gel electrophoresis.

Two-dimensional (2-D) gel analysis was used to examine differences in the levels of 19 plasma proteins: before and after an acute inflammatory reaction (parenteral typhoid vaccination) in normal subjects, between rheumatoid arthritis (RA) patients and normals and in RA patients treated with tenidap (120 mg) and piroxicam (20 mg). Typhoid vaccination increased levels of SAA, haptoglobin alpha1, haptoglobin alpha2, haptoglobin beta and alpha1-anti-chymotrypsin but decreased transthyretin and apolipoprotein E. In RA patients, serum amyloid A (SAA), haptoglobin alpha2, haptoglobin beta, alpha1-antichymotrypsin and C3 proactivator levels were elevated while apolipoprotein A-I, apolipoprotein A-IV, transthyretin, Gc-globulin, alpha2-HS glycoprotein, alpha2-macroglobulin and alpha1-B glycoprotein levels were decreased, compared to normals. Compared to piroxicam, tenidap lowered levels of alpha1-antiprotease and SAA but raised the levels of transthyretin, Gc-globulin, alpha2-HS-glycoprotein and alpha2-macroglobulin in RA patients. C-reactive protein (CRP) could not be quantified on 2-D gels but, when measured by rate nephelometry, levels were reduced after treatment with tenidap compared to piroxicam. The general pattern of the acute phase protein response to an acute inflammatory response to typhoid vaccination is similar to that in the chronic inflammatory condition, RA. The impact of tenidap on both positive and negative acute-phase proteins in RA patients could clearly be distinguished from that of piroxicam.

Human recombinant alpha 2-HS glycoprotein is produced in insect cells as a full length inhibitor of the insulin receptor tyrosine kinase.

Human Alpha 2-HS glycoprotein (AHSG), a glycoprotein synthesized by hepatocytes, was expressed in insect cells using the recombinant baculovirus system. The protein was purified from the cell supernatant, and appeared as a single band at about 52 kDa. Western blot using a specific antibody to the B-chain of AHSG indicated that the connecting peptide was present in the protein. When incubated with solubilized insulin receptors, recombinant AHSG inhibited the tyrosine kinase activity of the receptors in a dose-dependent fashion at concentrations in the range of those of the circulating protein. AHSG did not interfere with the binding of insulin to its receptor. These results indicate that human AHSG represents a natural inhibitor of the insulin receptor tyrosine kinase, is active as a single-chain protein and possesses a biological role similar to that of its homologue in rats, pp63, described by Auberger et al. (1).

Total synthesis of B-chain of human α2HS glycoprotein

B-chain of human α2HS glycoprotein 1, a cystein-containing heptacosapeptide carrying a trisaccharide (sialyl T) side chain, was synthesized for the first time by the solid-phase method utilizing a glycosyl serine building block 11 with benzyl protecting groups.

Structure of the gene encoding human alpha 2-HS glycoprotein (AHSG)

Alpha 2-HS glycoprotein (AHSG) is a human plasma glycoprotein and fetuin is the homologue in the calf. In this report, we present the structure and organization of the AHSG gene. Introns and the 5′ and 3′-flanking regions were obtained by polymerase chain reaction (PCR) and the inverted PCR, respectively, from genomic DNA using AHSG cDNA-specific oligonucleotide primers. The sequence of the PCR products shows that the coding region spans approximately 8.2 kb and is composed of seven exons interrupted by six introns. The exon–intron splice junctions agree with the consensus sequence, and the positions interrupted by introns are precisely identical to those of the rat insulin receptor tyrosine kinase inhibitor (fetuin) gene. The 5′-promoter region contains several characteristic sequences such as an A+T-rich sequence of TAAATAA, C/EBP-binding site, and hepatocyte nuclear factor-5 (HNF-5) and serum response factor (SRF) sites.

ACUTE PHASE RESPONSE ABNORMALITIES IN NEONATAL SEPSIS: A 2-D PAGE STUDY 52

The aim of this study was to analyze the acute phase protein response during early onset (<72 h) neonatal sepsis by high-resolution two-dimensional electrophoresis (2-D PAGE). Cord and serial plasma/serum samples from eight neonates with sepsis (positive blood culture) were examined(gestational age, median 33.5 weeks; range 24.3-40.6, pre-term: n=4 full term: n=4; birth-weight, median 2,635 g; range 600-3,400; onset at birth, n=6; at 7.5 h, n=1; at 48h, n=1). Isolated microorganisms were: S. agalactiae (n=4/8), C. striatum (n=2/1. 8), L. monocytogenes (n=1/8) and C. albicans (n=1/8). Admission to the Neonatal Intensive Care Unit was necessary for 7 infants (hospitalization time, median 22.5 days, range 5-82). Clinical outcome was favorable in 7 cases, lethal in one. Plasma/serum samples from five gestational age- and sex-matched control infants (repeated negative blood cultures; absent histological chorioamniositis and clinical symptoms) were also analyzed. 2D-PAGE was performed using an immobiline polyacrylamide system. Routine sample load was 0.75 μl. Isoelectric focusing was carried out on non-linear wide-range immobilized pH (3-10) gradients. The second dimension was performed on 9-16% SDS-PAGE linear gradient gels. Silver-stained gels were scanned with a computing densitometer. Image analysis and on-line matching were carried out using MELANIE II software (Biorad). Haptoglobin (Hpt) (n=8/8) and serum amyloid A protein (SAA)(n=5/8;term infants 4/4, pre-term 1/4) in cord blood were significantly correlated with sepsis, though they were absent among controls (p<0.001). Hpt and SAA spots were identified in silver-stained electrophoretograms, confirmed by immunoblotting with specific antibodies. Hptβ-chains appeared to be under-sialylated in pre-term infants, while post-translation modifications of α-chains and SAA were similar to those observed in the adult. Different Hpt α-chain phenotypes than those in maternal serum were observed, indicating that cord blood Hpt originates from neonatal synthesis. Inconsistent changes in typical acute phase proteins(α1-antitrypsin, α1-antichymotrypsin, leucine-richα2-glycoprotein, α2-HS glycoprotein, transthyretin and serum retinol-binding protein) were present. The findings indicate that the acute phase protein response in the newborn: 1) differs from those of other periods in life in that is limited to changes in Hpt and SAA; 2) is gestational age-dependent. Finally, the data suggest that cord blood Hpt and SAA may be potentially useful early markers for neonatal sepsis.

Molecular cloning and sequencing of cDNA encoding plasma countertrypin, a member of mammalian fetuin family, from the Mongolian gerbil, Meriones unguiculatus.

Complementary DNA clones coding for countertrypin were isolated from a liver cDNA library of the Mongolian gerbil, and sequenced. They contained one open reading frame encoding 348 amino acid residues, which were assigned to consist of an 18-residue signal peptide and a 330-residue mature protein. The amino acid sequence was about 74% identical with mouse countertrypin and rat fetuin, 60% with bovine fetuin, and 55% with human alpha2HS glycoprotein, indicating that this protein belongs to the mammalian fetuin family. The members of this family are known to consist of three domains, i.e., two tandemly arranged cystatin domains (D1 and D2) and an unrelated domain (D3) located at the C-terminal region. When compared with the other members of this family, D3, especially its N-terminal half, varies greatly with deletion or insertion as well as nucleotide substitutions even among three rodent species, i.e., gerbil, rat, and mouse. The sequence comparison also suggests that the conformation of human alpha2HS glycoprotein differs greatly from that of other members of this family. A molecular phylogenetic tree of 7 members, constructed on the basis of the synonymous substitution rate of D1 and D2, shows that the gerbil gene diverged prior to the separation of mouse and rat.

Molecular evidence for human alpha 2-HS glycoprotein (AHSG) polymorphism.

Alpha 2-HS glycoprotein (AHSG) is a human plasma glycoprotein that exhibits genetic polymorphism on isoelectric focusing (IEF). To identify the origin of two common alleles, AHSG*1 and *2, we examined nucleotide exchanges in the gene. AHSG cDNA was obtained by RT-PCR from poly(A) RNA of seven liver tissue samples and subcloned into a plasmid vector. After sequencing, we found six single nucleotide differences in comparison with the originally reported sequence. In particular, the nucleotide substitutions of C to T at amino acid position 230 and C to G at position 238 were common among the samples exhibiting phenotype 2-1 or 2. Since these substitutions might give rise to a NlaIII site and a SacI site, respectively, for the potential AHSG*2, we analyzed these substitutions by PCR-RFLP using genomic DNA of 68 individuals. The result was consistent with the IEF analysis of the corresponding serum, indicating that AHSG*1 was characterized by ACG (Thr) at position 230 in exon 6 and ACC (Thr) at position 238 in exon 7, and that AHSG*2 was characterized by ATG (Met) at position 230 and AGC (Ser) at position 238.