Polyclonal antibodies against the polypeptide and carbohydrate epitopes of recombinant human choriogonadotropin beta-subunit

Maturing Glycoproteomics Technologies Provide Unique Structural Insights into the N-glycoproteome and Its Regulation in Health and Disease

The glycoproteome remains severely understudied because of significant analytical challenges associated with glycoproteomics, the system-wide analysis of intact glycopeptides. This review introduces important structural aspects of protein N-glycosylation and summarizes the latest technological developments and applications in LC-MS/MS-based qualitative and quantitative N-glycoproteomics. These maturing technologies provide unique structural insights into the N-glycoproteome and its synthesis and regulation by complementing existing methods in glycoscience. Modern glycoproteomics is now sufficiently mature to initiate efforts to capture the molecular complexity displayed by the N-glycoproteome, opening exciting opportunities to increase our understanding of the functional roles of protein N-glycosylation in human health and disease.

cDNA cloning of canine common alpha gene and its co-expression with canine thyrotropin beta gene in baculovirus expression system

The common alpha gene of the canine glycoprotein hormones was cloned, sequenced and co-expressed with the canine thyrotropin beta (TSH beta) gene in the baculovirus expression system, and a bioactive recombinant canine TSH was purified. The canine common alpha gene was cloned from the total RNA extracted from the canine pituitary gland by the reverse transcription polymerase chain reaction (RT-PCR) using primers that were designed based on the consensus sequences from other species. The resulting 476 bp PCR product is consisted of the full coding sequence for the 96 amino acid mature alpha subunit, and a sequence encoding a 24 amino acid signal peptide. Homology analysis with other species revealed that the canine common alpha subunit potentially contains five disulfide bonds and two oligosaccharide chains N-linked to Asn residues located at positions 56 and 82. For expression in the baculovirus expression system, the common alpha gene was cloned downstream of the p10 promoter of the pAcUW51 transfer vector, and the previously cloned canine TSH beta gene was inserted under the polyhedrin promoter of the same vector. The recombinant virus containing both alpha and beta genes was generated and propagated before being used to transfect the Sf9 insect cells for expression. The medium from the Sf9 cultures, presumably containing canine TSH alpha and beta in native heterodimer confirmation, exhibited TSH bioactivity as indicated in the cAMP stimulation assay in FRTL-5 cells. The expressed recombinant protein was purified from the culture medium with an affinity column that was coupled with IgG purified from the polyclonal antibodies generated against the partially purified native canine TSH.

Definition and measurement of follicle stimulating hormone

FSH has a key role in the development and function of the reproductive system and is widely used both diagnostically and therapeutically in developmental and reproductive medicine. The accurate measurement of FSH levels, in patients for diagnosis and monitoring and in therapeutic preparations for clinical use, is essential for safe and successful treatment. Historically, FSH was defined on the basis of classical in vivo endocrine activity, and early therapeutic preparations were calibrated using in vivo bioassays. There was early recognition that reference preparations were required for calibration if the results from different laboratories were to be comparable. In response to the perceived need, the World Health Organization established the first standard for such preparations in 1959. Subsequent developments in biotechnology have led to recognition that there is no single molecule that can be uniquely defined as FSH, and that FSH can induce a range of biological activities. Several highly purified standards for FSH are now available, but discontinuity and heterogeneity of estimates of FSH activity in terms of these standards made using in vitro assays and binding assays have been noted. It is thus essential that any measurement of FSH include specification both of the standard with which the measured FSH is compared and the assay method used for that comparison.

Do immunoassays differentially detect different acidity glycoforms of FSH?

OBJECTIVE

The possibility of the carbohydrate residues of glycoproteins affecting their recognition in immunoassays is an important and unresolved issue. This study looked for evidence of differential recognition of FSH glycoform preparations, of variable isoelectric point (pI) and known molarity, using three routine assays employing different antibody configurations.

DESIGN

Seven glycoform preparations with differing pI bands (between 3.8 and 5.5) were produced by isoelectric focusing of recombinant human FSH and the molecular weights determined by mass spectroscopy. Three concentrations of each glycoform were assayed and the results expressed relative to unfractionated material. From the relative responses, recognition differences between the assay methods and between the glycoform preparations were investigated.

MEASUREMENTS

Three routine assays were employed: the commercially available Amerlite(R) enzyme immunoassay and Delfia(R) immunofluorometric assay, together with an in-house competitive two-site radioimmunoassay (RIA).

RESULTS

Overall, the three assays gave the same relative responses for equivalent glycoforms, with the only exceptions involving small differences between some assay pairs for the fractions at the extremes of the pI range investigated. Within each assay type, differences (P < 0.05) of up to 33% existed between glycoforms of different pI, however, these differences showed no patterns or trends across the entire acidity range examined.

CONCLUSIONS

Between the assay methods investigated in this study, few differences exist in the recognition of individual pI bands of FSH when expressed relative to a common unfractionated standard. Differences were apparent in the recognition of the different acidity glycoforms within each assay method, however, these were small and unlikely to be of clinical significance.

Structural and functional characterisation of hFSH and hLH isoforms

Human follicle-stimulating hormone (hFSH) and luteinizing hormone (hLH) are gonadotropins which are secreted as multiple forms by the pituitary. Evidence supporting the structural and functional heterogeneity of 15 purified hFSH isoforms and 20 purified hLH isoforms from pituitary extracts will be presented. Gonadotropin isoforms were purified by a combination of preparative isoelectric focusing and ion-exchange chromatography. The protein mass of each isoform was determined by amino acid analysis, which also correlated (data for hLH) (r = 0.999, P < 0.001, n = 15) with the UV area under the curve at 280 nm of the isoforms following gel-filtration HPLC. The alpha and beta subunits of FSH and LH were shown to be intact by SDS-PAGE under reducing condition, with no evidence of proteolytic nicking or presence of contaminating proteins. hFSH radioreceptor activity varied over a seven-fold range, and a positive correlation (r = 0.85, P < 0.001, n = 9) was observed between FSH receptor activity and the sialic acid (SA) content (1.5-13.7 mol SA/mol hFSH) of the isoforms, as determined by an HPLC-based microfluorometric assay. FSH in vitro activities varied over a similar range with a high correlation (r = 0.82, n = 15) with receptor activities, suggesting that the initial association of the hormone with the receptor is the key interaction with less differences attributed to subsequent effects in the signaling pathway. A similar result was seen with the hLH isoforms. To explore FSH/LH in vivo, the circulating half-life (LH/FSH) and the in vivo bioactivity (LH) using an acute in vivo assay was investigated. The clearance of hLH and hFSH showed a bi-exponential pattern for all isoform preparations with the proportion of the slower dissociating component (t 1/2 50-60 min) increasing three-fold with increasing sialic acid content of the isoform. The more rapidly cleared component (t 1/2 approx 10 min) is attributed to hepatically cleared gonadotropin, rather than gonadotropin equilibration between body compartments. The in vivo assay procedure for LH was based on the 24 h integrated plasma testosterone levels in rats following administration of graded doses of hLH isoform or standard. A 16-fold range in vivo activities between LH isoforms (n = 14) was observed. A comparison between hLH in vitro and in vivo activities showed a good correlation (r = 0.75) with the slope of the regression line (1.39) not significantly different from unity. These results suggest that in this acute in vivo assay method, the differences in circulating half-lives between hLH isoforms although large is not a key factor in their in vivo activity. However, in chronic in vivo assay systems the differences in clearance rates between isoforms may be important in their subsequent biological response. It is concluded that structural heterogeneity of FSH and LH contributes to functional differences, with a key interaction occurring at the receptor level. The contribution of sialic acid to these activities was also investigated.

Immunogenicity of the N-glycans of peanut peroxidase

The three tryptic glycopeptides of cationic peanut peroxidase (C. PRX) and the sole one of anionic peanut peroxidase (A. PRX) were individually coupled to bovine serum albumin to raise antisera. The three categories of antibodies directed towards three N-glycans of C. PRX (anti-GLa, anti-GLb and anti-GLc) were isolated from antisera with glycan-conjugated ECH Sepharose 4B affinity columns and the distribution of epitopes on the N-glycans was investigated. The reactivity of anti-GLa, anti-GLb and anti-GLc is inhibited 25-40% by 1 M fucose, compared with a slight inhibition by N-acetylglycosamine and xylose. Mannose and galactose showed no inhibition to anti-GLa and only a slight inhibition to anti-GLb and anti-GLc. All of anti-GLa, anti-GLb and anti-GLc recognize A. PRX and horseradish peroxidase but do not recognize fetuin. Also, their reactivity is inhibited by bromelain by more than 70%. The three categories of antibodies present high homogeneity and appear to be directed mainly towards the core structure [Xyl] (Man)3 [Fuc] (GlcNAc)2. An effective and simple method to screen antibodies with carbohydrate specificities is described herein.

Less acidic forms of luteinizing hormone are associated with lower testosterone secretion in men on haemodialysis treatment

OBJECTIVE

Men with chronic renal failure treated by haemodialysis have raised levels of bioactive LH (B-LH) and immunoreactive LH (I-LH) but reduced B-LH:I-LH (B:I) ratio and testosterone (T) secretion. This study investigated the LH isoform distribution in serum from normal adult males and males on regular haemodialysis treatment.

DESIGN

Four blood samples (2 ml) were obtained at 15-minute intervals from a group of men on regular haemodialysis treatment. These samples were part of a larger pulse profile series and showed no evidence of LH pulsatility. The serum was pooled for each individual patient. Blood (10 ml) was also drawn randomly from healthy male volunteers. The sera were chromatofocused on a 4-ml mono-P column attached to a fast performance liquid chromatography system. This procedure separates the LH isoforms according to their isoelectric point. The pH gradient was between pH 7 and pH 4.

PATIENTS

The five men with chronic renal failure were aged between 18 and 40 years and had been on haemodialysis for a mean of 10 months (5-20). They were sampled the night prior to a dialysis session. The five normal healthy volunteers had never had any endocrine disorder diagnosed.

MEASUREMENTS

An immunoradiometric assay and a commercially available (Delfia) immunofluorimetric assay were employed for detection of LH in the sera and in chromatofocusing fractions. B-LH and testosterone were also measured in the sera.

RESULTS

Hormone data (mean +/- SEM for normal and renal subjects respectively) were 15.5 IU/l +/- 1.2 and 26.9 +/- 7.2 (B-LH), 6.0 IU/l +/- 0.3 and 16.5 +/- 4.8 (irmaLH), 5.7 +/- 0.5 and 13.6 +/- 4.8 (fluorLH), 25.2nmol/l +/- 2.0 and 12.1 +/- 1.2 (T). The serum B:I ratios were 2.6 +/- 0.1 and 2.6 +/- 0.2 (controls, irmaLH and fluorLH respectively) and 1.7 +/- 0.1 and 2.1 +/- 0.1 (chronic renal failure group). Recovery of LH from the column was 111 +/- 12% (mean +/- SEM) by IRMA and 104 +/- 7% by IFMA for the ten FPLC runs. The median pI for the LH distribution measured by both assays was in the region 6.54-6.40 for subjects with chronic renal failure and 6.09-5.95 for controls. Median pI was negatively correlated to the B-LH:irmaLH (P < 0.0001) and B-LH:fluorLH ratios (P = 0.002) in the serum. Furthermore, the proportion of isoforms recovered in the pH region 6.25-5.50 increased with increasing T levels in the serum (P < 0.004).

CONCLUSION

The distribution of LH in serum of men on haemodialysis is more basic than in normal men. The greater the proportion of more acidic LH species, particularly those with a pI of between 5.50-6.25, the higher the ratio of LH bioactivity to immunoactivity and consequently testosterone levels.