Carbon/Kevlar/PEEK Thermoplastic Composites

Thermoplastic composites were developed from carbon/hybrid (1: 1)/Kevlar fabrics using a high-performance polyether ether ketone (PEEK) matrix. The mechanical properties and microstructure of the composites show that the type of fiber has a strong influence on the fiber-matrix bonding and fracture behavior of the composites. The fracture energy of the composites was of the order of -30 kJ m-2 for carbon/PEEK and hybrid/PEEK composites.

Role of amino acid residues at the interface of alpha52asparginyl-N-glycosyl chain of human choriogonadotropin

Of all the four N-glycosyl chains present in hCG, only one of them at alpha52Asn is located at the alpha/beta subunit interface and is crucial for the biological function of the hormone. The other three are exposed on the surface of the molecule and play only a minor role in the function of the hormone. The alpha52Asn oligosaccharide interacts with five amino acid residues in the beta-subunit, Tyr59, Val62, Phe64, Ala83, and Thr97. The present studies were undertaken to determine the role of the residues at the alpha52Asn-oligosaccharide and the beta-subunit interface in the mechanism of subunit association and downstream signaling events. Ten mutants, two of the alpha-subunit by the replacement of Asn52 and Thr80 with Gln and eight of the beta-subunit by multiple or single amino acid mutations, were prepared. These mutants included, hCGbeta59,62,64,97Ala, hCGbeta59,62,64Ala, hCGbeta62,64Ala, hCGbeta59Phe, hCGbeta62Ala or Thr, hCGbeta83Ile and hCGbeta97Ala. The mutation of the Asn52 to Gln resulted in a drastic change in its conformation and as a consequence in its weak affinity with the wild type beta as compared with that of the wild type hCGalpha and hCGalpha80Gln. The mutants with mutations in the four or three amino acids as well as both mutants of hCGbeta62Val almost failed to combine with hCGalpha again as a result of conformational changes shown by circular dichroism (CD) analysis and not due to their direct involvement in the subunit association. The double mutant combined with hCGalpha and the heterodimer behaved more like the wild type hCG. The mutation of Tyr to Phe resulted in a drop of 20% in the receptor binding and cAMP stimulation although Tyr is considered to be involved directly in subunit association. HCGbeta with mutations in the other amino acids, Phe64, Ala83, and Thr97, combined with the alpha subunit forming heterodimers with biological activity comparable to that of the wild type hCG. Thus, it appears that among the five amino acids in the vicinity of alpha52Asn carbohydrate, only beta59Tyr and beta62Val may be involved directly or indirectly in the alpha/beta beta dimer formation.

Effect of individual N-glycosyl chains in the beta-subunit on the conformation of human choriogonadotropin

Human choriogonadotropin is a heterodimeric glycoprotein hormone comprised of noncovalently associated alpha- and beta-subunits. Each of the subunits has two N-glycosyl chains. In our previous communication, we investigated the role of individual carbohydrate chains in the alpha-subunit on the signal transduction function and conformation of the hormone. This paper deals with the effect of individual or both N-glycosyl chains in the beta-subunit on the function and conformation of the monomer as well as of the heterodimer. Three mutants each of hCGbeta and hCG lacking N-glycosyl chains at beta13Asn, beta30Asn and beta13,30Asn were prepared by site-directed mutagenesis by replacing Thr residues in the recognition triplet sequence at beta15 and beta32 positions with Gln. All mutant heterodimers had receptor binding and cAMP and progesterone stimulating activities comparable to wild type hCG. While the loss of carbohydrate at beta13Asn or beta13,30Asn in the case of hCGbeta monomer resulted in a 4-6%, decrease in the ordered structure, the loss of the glycosyl chain at beta 30Asn did not alter the conformation as compared with the wild type hCGbeta. Similarly, all carbohydrate deficient hCG heterodimers had a decrease of 6-8%) in the ordered structure as compared with hCG. Thus, while the individual N-glycosyl chains did not affect the function of the hormone, they did have marked effect on its conformation but the conformational changes were localized and did not perturb the receptor binding and signal transduction sites.

Mutants of human choriogonadotropin lacking N-glycosyl chains in the alpha-subunit. 1. Mechanism for the differential action of the N-linked carbohydrates

Analogs of human choriogonadotropin (hCG) lacking N-glycosyl chains at alpha52Asn and alpha78Asn were purified from the culture media of insect cells by immunoaffinity chromatography using a monoclonal antibody column. As previously reported, while analogs lacking carbohydrate at alpha52Asn and alpha78Asn had similar receptor binding activities compared with the wild type recombinant hCG (hCGwt), they differed in their signal transduction properties. The mutant lacking carbohydrate at alpha78Asn had 20% less cAMP-stimulating activity than hCGwt, but the absence of glycosylation at alpha52Asn resulted in the reduction of cAMP accumulation by 90-95%. A similar effect of the mutations was observed on the stimulation of steroidogenesis. Circular dichroism spectra of the two mutants showed significant differences. The mutant lacking carbohydrate at alpha52Asn had a much higher negative mean residue ellipticity (MRE) at 200 nm and a lower negative MRE at 220 nm than that lacking carbohydrate at alpha78Asn and hCGwt. The dissociation rates of the alpha52Asn and alpha78Asn carbohydrate deficient mutants at pH 3 and room temperature, measured by using 1-anilino-8-naphthalenesulfonate, were 9.4 x 10(-5) and 3.8 x 10(-5) s-1, respectively, as compared with 1.5 x 10(-5) s-1 for hCGwt. The results of both CD measurements and dissociation studies strongly suggest that the absence of carbohydrate at alpha52Asn results in conformational changes in the mutant which might explain the loss in its signal transduction function. This is further supported by indirect evidence from two other lines of experimentation. Unlike the mutant lacking carbohydrate at alpha78Asn, the one lacking carbohydrate at alpha52Asn cross-reacted with the two subunit specific monoclonal antibodies, anti-hCGalpha and anti-hCGbeta, which normally did not cross-react with the native or the hCGwt. Also, polyclonal anti-hCGbeta but not anti-hCGalpha was able to restore the cAMP-producing activity of the alpha52Asn carbohydrate deficient mutant. From all the data taken together, it appears that the loss of second messenger-producing activity of hCG with the absence of the glycosyl chain at alpha52Asn was probably due to a conformational change in the heterodimer rather than due to the loss of the alpha52Asn-carbohydrate-receptor interaction.

Effect of modification of the beta-hairpin and long loops simultaneously in both alpha- and beta-subunits on the function of human choriogonadotropin: part II

According to the X-ray diffraction, human choriogonadotropin has four beta-hairpin and two long loops, equally distributed in each of the alpha and beta subunits. Radical mutations such as the replacement of alpha 18Phe and alpha 74Phe with Thr in the alpha1 and alpha3 loops respectively and the replacement of alpha 45Lys with Asp in the alpha2 loop in the alpha-subunit were introduced while the loop sequences in the beta-subunit were replaced with the corresponding sequences in hFSH beta. Nine different double mutants with simultaneous mutations in both the alpha and beta loops including hCG alpha1 beta1, hCG alpha1 beta2, hCG alpha1 beta3, hCG alpha2 beta1, hCG alpha2 beta2, hCG alpha2 beta3, hCG alpha3 beta1, hCG alpha3 beta2 and hCG alpha3 beta3 were partially purified from insect High-Five cells. As previously reported (Shao et al., 1996, Mol. Cell. Endocrinol. 122, 173-182), the mutation in the alpha1 loop in the mutant, hCG alpha1 beta, the mutants hCG alpha1 beta1 and hCG alpha1 beta3 caused 200%, increase in the receptor binding, cAMP and progesterone stimulation. The mutant, hCG alpha1 beta2 and all other mutants behaved like the recombinant hCG (rehCG) in the receptor binding and post-receptor signaling activities. The molecular cause for this increase is probably due to a conformational change in the heterodimers caused by the mutation in the alpha1 loop. This conclusion is based on the results of the dissociation studies of the mutants heterodimers which indicated a decreased affinity between the subunits. The first order rate constants for the dissociation of the mutants hCG alpha1 beta1, hCG alpha1 beta2 and hCG alpha beta3 were 3.7 x 10(-2) min(-1), 1.4 x 10(-2) min(-1) and 4.6 x 10(-2) min(-1) respectively, as compared with 4.6 x 10(-3) min(-1) for the rehCG. It seems from the data that alpha 18Phe is located in, or in proximity to the receptor binding site and probably plays a critical role in maintaining either directly or indirectly its conformational integrity.

Effect of modification of all loop regions in the alpha- and beta-subunits of human choriogonadotropin on its signal transduction activity

Human choriogonadotropin (hCG), according to its three dimensional structure as determined by X-ray diffraction, has three beta-hairpin loops each in the alpha and beta subunit designated as alpha 1, alpha 2 alpha 3 and beta 1 beta 2 and beta 3, respectively. Since similar beta-hairpin loops in NGF and TNF beta have been implicated in their direct interaction with the receptor, it prompted the present investigation to determine the role of such loops in receptor binding and post-receptor signaling events in hCG. Based on the three dimensional structure of hCG, radical mutations were introduced in the alpha loops by replacing hydrophobic alpha 18Phe and alpha 74Phe by hydrophilic Thr residues in the alpha 1 and alpha 3 loops, respectively, and positively charged alpha 45Lys by negatively charged Asp in the helical segment in the alpha 2 loop. The beta loops were mutated by replacement of the beta 1, beta 2 and beta 3 sequences with the corresponding hFSH sequences. These replacements included beta 22Gly, beta 24Pro and beta 25Val with Glu, Arg and Phe in beta 1, 45Leu Gln Gly Val Leu Pro Ala Leu Pro53 with Tyr Lys Asn Pro Ala Arg Pro Leu Ile in beta 2 and 73Pro Arg Gly with Ala His His in the beta 3 loop. Six mutants, hCG alpha 1 beta, hCG alpha 2 beta and hCG alpha 3 beta and hCG alpha beta 1, hCG alpha beta 2 and h CG alpha beta 3, were obtained by co-infection of the insect High-Five cells with baculovirus containing mutant alpha or beta cDNAs and that containing complimentary wild type beta or alpha cDNAs. The mutants were almost completely secreted in the culture medium and were over expressed at levels ranging between 4.5 to 29 micrograms/ml indicating that mutations had no effect on the secretion or subunit assembly of hCG. In order to remove any contaminating beta-subunit, the culture medium was passed through a column of an hCG beta-specific monoclonal antibody, B158. The receptor binding activity of the mutant hCG alpha 1 beta, in which alpha 18Phe was replaced with Thr, increased almost 200% relative to rehCG. Similarly, increase in the cAMP and progesterone stimulation by the mutant ranged between 150 to 200%. This increase is believed to be due to a short range conformational change in the mutant as a result of the mutation rather than direct involvement of alpha 18Phe in the receptor binding. The evidence in support of this was derived from the fact that the affinity or interaction between the two subunits was impaired as indicated by the first order rate constant of hCG alpha 1 beta (km = 4.1 x 10(-2) min-1) at pH 3.0 at 23 degrees C which is one order of magnitude greater relative to rehCG (kw = 4.6 x 10(-3) min-1). All other mutations had no effect on the receptor binding or signal transduction of hCG indicating that, unlike NGF or TNF beta, beta-hairpin loops in hCG were not directly involved in receptor binding or post-receptor signaling events. However, since the mutation in the alpha 1 loop affects the receptor binding site, its presence in the vicinity of the alpha 1 loop is highly likely.

Preparation of recombinant carbohydrate deficient active analogs of human chorionic gonadotropin from insect cells

Human chorionic gonadotropin (hCG) has four N-glycosyl chains, two in each subunit. Several analogs lacking one or more specific N-linked carbohydrate chains have been purified from insect cells by immunoaffinity chromatography on a monoclonal antibody, B17, column Traces of the hCG beta mutant present, if any, were removed by a second immunoaffinity chromatography on a column of hCG beta specific monoclonal antibody, B158. N-glycosylation was inhibited by the replacement of either Asn or Thr to Gln in the consensus sequence. -Asn x Ser/Thr-, for N-glycosylation. All analogs were overexpressed in High-Five insect cells with the expression levels ranging between 1.5 to 15 micrograms/ml and were found homogeneous by SDS-PAGE under nonreducing and reducing conditions. Their molecular sizes ranged between 34k to 44k. The receptor binding affinity of all the analogs was unaltered as determined by radio receptor assay using rat ovarian membranes. The availability of these analogs should facilitate studies on the effect of a specific carbohydrate chain on the conformation and in vivo properties of hCG.

[Expression of the extracellular domain (1-341) of rat ovarian lutropin receptor in insect cells and preliminary characterization of the expressed product]

Extracellular domain residues 1-341 (designed R 341) of luteinizing hormone/human chorionic gonadotropin receptor (LH/hCG receptor) has high binding affinity for ligand. This paper describes expression of cDNA coding for R 341 in insect cells and preliminary identification of the expressed protein. SDS-PAGE silver staining and immunoblotting analysis show expressed product appears in two bands, major band has molecular weight 38.5 Kd, and weak band, 40.0 Kd. Ligand binding immunoblotting and 125I-hCG-binding blotting analysis indicate that expressed product R 341 has specific binding affinity for ligand. Ligand binding assay and Scatchard analysis indicate that recombinant receptor R 341 has high binding affinity for hCG and Kd is 5.68 x 10(-10) mol/L.

[Cloning and overexpression of rat ovary LH/hCG receptor cDNA in insect cells]

Luteinizing hormone/human chorionic gonadotropin receptor (LH/hCG receptor) is a glycosylated protein coupled with G-protein. This paper reports screening of LH/hCG receptor cDNA from rat ovary cDNA library and the overexpression of the cDNA in insect cells. Full length of LH/hCG receptor cDNA is 2403 bp encoding signal peptide and matured protein of LH/hCG receptor. The cDNA is overexpressed in insect cells using baculovirus expression vector pVL 1393. The apparent molecular weight of purified receptor using immunoaffinity chromatography is 120 Kd and 92 Kd under non-reducing and reducing conditions, respectively. Ligand binding assay and Scatchard Plot analysis indicates that Kd is 8.4 x 10(-9) mol/L which is similar to that of the purified receptor from CHO cells.

High expression of the hormone binding active extracellular domain (1-294) of rat lutropin receptor in Escherichia coli

Using the polymerase chain reaction (PCR) technique, the cDNA fragment corresponding to the receptor coding region for residues 1-294 was prepared from rat lutropin receptor (LHR) cDNA and subsequently subcloned into Escherichia coli expression vector pT7-7. This truncated receptor was efficiently expressed in E. coli as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining. The recombinant protein present in the inclusion bodies was solubilized in 6 M guanidine-HCl and purified in two successive steps of fast performance liquid chromatography (FPLC) using Superose-12 and Mono Q columns. Refolding of the purified recombinant protein was achieved in 1.5 M guanidine-HCl in the presence of an equimolar proportion of cysteine and cystine. The refolded soluble truncated LHR(1-294) had apparent molecular weights of 33 kDa and 140 kDa under reducing and nonreducing conditions, respectively. The multimeric nature of the extracellular domain of the receptor is believed to be due to its self-association by intermolecular disulfide bond formation since the 1-294 amino acid segment has nine cysteine residues and thus has one or possibly more free sulfhydryl groups. The purified truncated receptor had high binding affinity for human choriogonadotropin (hCG) as indicated by ligand blotting on SDS-PAGE and radioligand receptor assays. The amount of hCG required for 50% inhibition of binding of 125I-hCG to the soluble truncated receptor was 2.7 x 10(-10) M (or 12.25 ng). Similarly, the amount of soluble truncated receptor required for 50% inhibition of 125I-hCG binding to the rat ovarian receptor in the radioligand receptor assay was 58 ng.(ABSTRACT TRUNCATED AT 250 WORDS)

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

In our previous paper (Chen et al. (1991) J. Biol. Chem. 266, 4081-4087) we reported the preparation and characterization of recombinant human choriogonadotropin beta subunit (hCG beta) using the baculovirus-insect cell expression system. The rhCG beta was found to contain high mannose type N-linked carbohydrates and 3-4 serine-linked disaccharide chains. Despite the carbohydrate structural variation, the rhCG beta was similar to hCG beta in in vitro immunological and biological properties. In order to evaluate its in vivo immunological properties, rabbit antiserum against rhCG beta was produced. The antiserum was found to be almost identical to anti-hCG beta in binding to hCG beta as well as in its crossreactivity with human lutropin (hLH), hCG and human follitropin (hFSH) as indicated by radioimmunoassays using 125I-hCG beta as a tracer. Further characterization of the anti-rhCG beta antiserum revealed that there are three types of antibodies in terms of antigenic specificity present in the anti-rhCG beta antisera pool as shown by dot blot and radioimmunoassays. The carbohydrate-specific antibodies were separated by affinity chromatography using an ovalbumin-glycopeptide-Sepharose column. The antibodies held on the ovalbumin affinity adsorbent were specific for the high mannose type carbohydrates such as those present in rhCG beta, rhCG and thyroglobulin and failed to react with transferrin, alpha 1-acid glycoprotein and hCG alpha, all containing complex type carbohydrates. This was further supported by the fact that the recombinant unglycosylated hCG or periodate oxidized rhCG beta also did not show any reactivity with the carbohydrate specific antibodies. Two types of peptide epitopes seemed to be present in rhCG beta since when the flowthrough fraction from the ovalbumin-glycopeptide-affinity column was passed through the hCG beta-Sepharose column, the antibodies in the flowthrough from the latter column were specific to the unique antigenic determinants present only in the rhCG beta and not in hCG beta. The eluate from the hCG beta-Sepharose column contained the third type of antibodies, being the predominant ones, directed to the common epitopes between rhCG beta and hCG beta. The high mannose type specific antibodies are potentially useful in differentiating between the high mannose and complex type of N-linked carbohydrates present in a glycoprotein. Also, the antibody could provide an effective reagent in studying the intracellular processing of the N-linked oligosaccharides.(ABSTRACT TRUNCATED AT 400 WORDS)

Human choriogonadotropin-induced coupling of receptor and Gs protein and the effect of hormone deglycosylation

The detergent-soluble extract of rat ovary plasma membranes contained a Gs protein of about 100 kDa as shown by its elution behavior on a Bio Gel A-1.5m column. However, the cell membranes exposed to hCG (37 degrees C, 15 min) contained in addition a higher molecular weight Gs protein complex of 300 kDa comprised of human chorionic gonadotropin (hCG) receptor (hCGR) and Gs. The complex bound with an affinity column of GTP-Sepharose and could be released with Gpp(NH)p and GTP inhibited this binding. The presence of the hCGR in the complex was shown by its binding to 125I-hCG. Furthermore, GTP inhibited the binding of hCG to the complex. These results indicate the presence of hCGR and Gs protein complex in the hCG-treated membranes. hCGR and Gs protein were individually purified and reconstituted into phospholipid vesicles. The protein-phospholipid vesicles showed saturation kinetics of binding of 125I-hCG and 3H-Gpp(NH)p. Incubation of phospholipid vesicles with hCG resulted in a 2-3-fold increase in the binding of 3H-Gpp(NH)p and GTPase activity. Activation of Gs protein was dependent on the length of incubation and the hormone concentration. Deglycosylated hCG was about 10 times less potent than hCG suggesting a role of carbohydrates of hCG in inducing hCG-Gs protein interactions. The data with the in vitro reconstitution system rule out the involvement of a carbohydrate-binding lectin in the function of the hormone.

Selenomethionyl analog of recombinant human choriogonadotropin

Selenomethionyl and high mannose type analog of recombinant human choriogonadotropin (hCG) to solve the crystallization and phase problems has been obtained by gene transfer methodology. SF9 insect cells were infected with the recombinant viruses containing hCG alpha and hCG beta cDNAs in selenomethionine containing methionine-free Grace's medium. The selenomethionyl hCG (SehCG) was purified from the culture medium by one step immunoaffinity chromatography using an immobilized monoclonal antibody against hCG beta. The presence of selenomethionine was demonstrated by amino acid analysis of SehCG. The amino acid composition indicated that more than 84% of methionine residues were substituted by selenomethionine. Its sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis yielded a single 38-kDa protein band under nonreducing conditions. The carbohydrate analysis of SehCG was consistent with the presence of four N-linked high mannose type carbohydrates and four O-linked simple disaccharide chains. The in vitro immunological and biological studies of SehCG indicated that selenomethionine substitution had no effect on the immunopotency, receptor binding, and steroidogenic activities of the hormone.

Recombinant carbohydrate and selenomethionyl variants of human choriogonadotropin

Recombinant human choriogonadotropin and selenomethionyl human choriogonadotropin (rhCG and SehCG) were expressed in baculovirus expression system by coinfection of SF9 insect cells by recombinant viruses, AcMNPV-hCG alpha and AcMNPV-hCG beta containing hCG alpha and hCG beta cDNAs. The expression efficiency of both rhCG and SehCG was quite high. The association of the alpha and beta subunits into a dimer was apparently complete since no detectable amount of rhCG beta was found in the rhCG eluate from the monoclonal hCG beta antibody immunoaffinity column. Both rhCG and SehCG preparations were homogeneous as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse-phase high performance liquid chromatography. The apparent molecular mass of rhCG and SehCG on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions was about 38 kDa while under reducing conditions the heterodimer dissociated to yield beta and alpha subunits with molecular masses of 22.5 and 18 kDa, respectively. The carbohydrate analysis of rhCG showing the presence of 2.1, 3.3, 7.38, 4.2, and 27.8 residues of Fuc, GalNAC, GlcNAC, Gal, and Man, respectively, per mole of the hormone was consistent with the presence of 4 N-linked high mannose type carbohydrate hydrate and 4 O-linked simple carbohydrate chains, probably made up of Gal-GalNAC. Despite the altered glycosylation, rhCG demonstrated close similarity to the native urinary hCG in amino acid composition, receptor binding, and in its ability to stimulate cAMP and steroidogenesis. This indicates that there is no specificity of carbohydrate required for biological activity. Furthermore, it implies that the alteration from the complex to high mannose type carbohydrates in rhCG does not affect its proper folding. Finally, amino acid analysis of SehCG showed that 84% of methionine residues in rhCG were replaced by selenomethionine.

Recombinant carbohydrate variant of human choriogonadotropin beta-subunit (hCG beta) descarboxyl terminus (115-145). Expression and characterization of carboxyl-terminal deletion mutant of hCG beta in the baculovirus system

A recombinant analog of human choriogonadotropin beta-subunit descarboxyl-terminal peptide (115-145 residues, delhCG beta) was obtained by the expression of corresponding beta cDNA in the baculovirus expression system. The efficiency of expression and secretion was high. The recombinant delhCG beta was purified by immunoaffinity using a specific monoclonal antibody against hCG beta and reverse phase high performance liquid chromatography. The hCG beta analog lacked the carboxyl-terminal 31-residue peptide as well as the four O-linked carbohydrates. Also, the N-linked "complex" type carbohydrates in the deletion mutant were modified to the high mannose type. The apparent molecular weights of delhCG beta in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions were found to be 19,000 and 27,500 respectively. delhCG beta on hydrolysis with endo N-acetylglucosaminidase F or H yielded a 17,500 protein band whereas treatment with N-glycanase gave a protein band with a molecular weight of 16,000. The carbohydrate analysis of delhCG beta, calculated on the basis of 4 residues of N-acetylglucosamine, showed 3 or 4 fucose, 0.6 N-acetylgalactosamine, and 11.4 mannose residues, indicating the high mannose type structures of the two N-linked carbohydrate chains. Despite the carbohydrate modification of the N-linked carbohydrates and the carboxyl-terminal deletion, the delhCG beta had about 87% of the immunological activity of the native hCG beta, indicating no significant conformational alteration induced by the mutation. The delhCG beta combined readily with native hCG alpha, and the reconstituted hCG alpha del beta required 0.031 pmol to achieve 50% inhibition of binding of the tracer with rat lutropin/choriogonadotropin receptor compared with 0.039 pmol by native hCG. Like native hCG, hCG alpha del beta also had most comparable ability to stimulate cAMP accumulation and progesterone production in rat Leydig cells. Thus it is clear from the data that the carboxyl-terminal deletion and thereby the deletion of four O-linked carbohydrates had no effect on its in vitro immunological and biological properties.

Carbohydrate variant of the recombinant beta-subunit of human choriogonadotropin expressed in baculovirus expression system

The beta-subunit of human choriogonadotropin (hCG) has two complex type N-linked and four O-linked carbohydrate chains. To further evaluate the specificity of the carbohydrate moiety on the hCG function, we have expressed hCG beta subunit in the baculovirus insect cell system to modify its carbohydrate structures. The recombinant hCG beta (rhCG beta) was efficiently secreted in the medium and was purified to homogeneity by immunoaffinity chromatography using a highly specific monoclonal antibody against hCG beta. The homogeneity of the recombinant subunit was established by sodium dodecyl sulfate-polyacrylamide gel electrophoresis performed under reducing and nonreducing conditions and reverse phase high performance liquid chromatography. rhCG beta had molecular weights of 22,500 and 33,000 under reducing and nonreducing conditions, respectively. Digestion with N-glycanase cleaved the Mr = 22,500 protein to 18,000, while digestion with Endo H or Endo F yielded an additional protein band of 20,500 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The carbohydrate analysis by pulse amperometry yielded the relative number of 2.5, 2.4, 3.7, and 11.3 residues of fucose, N-acetylgalactosamine, galactose, and mannose, respectively, based on a value of 4 residues for N-acetylglucosamine. Lectin binding studies showed rhCG beta to bind with concanavalin A with a high affinity and not with wheat germ agglutinin. In the studies with endoglycosidases together with the carbohydrate analysis and lectin binding properties, rhCG beta appears to have two high mannose-type N-linked and three to four O-linked carbohydrate simple disaccharide chains. The carbohydrate modification of the beta-subunit did not alter its immunopotency and its ability to combine with hCG alpha. The reconstituted hormone made up of rhCG beta and hCG alpha was found to be similar to hCG in biological properties such as receptor binding and in its ability to stimulate cAMP and steroidogenesis.

cDNA-derived amino acid sequences of choriocarcinoma alpha- and beta-subunits of human choriogonadotropin

Although amino acid sequences of the alpha- and beta-subunits of human choriogonadotropin (hCG) are known, only limited information is available on the disease state hCG. We have examined the amino acid sequences of the alpha- and beta-subunits of hCG from choriocarcinoma BeWo cells. The amino acid sequences were derived from the nucleotide sequences of BeWo cDNA clones of hCG alpha- and beta-subunits and were found to be identical with those of the normal subunits. It appears that the differences between the normal and the choriocarcinoma alpha- and beta-subunits of hCG reside primarily in the carbohydrates rather than the amino acid sequences. It may be pointed out that although coding and non-coding regions of BeWo cDNA clones of CG alpha and CG beta had several base changes from the hCG alpha and hCG beta cDNAs, these changes did not result in the alteration of their amino acid sequences. The longest BeWo alpha and beta cDNAs were 719 and 878 base pairs (bp) in length and lacked only 16 and 7 bp from the transcription start sites respectively. BeWo CG alpha cDNA had two base changes in the non-coding regions, one insertion of C at position 39 and another substitution of T for A at position 651, the latter change deleted one HindIII polymorphous site. The BeWo CG beta cDNA also had two base substitutions, A for G at 131 in the non-coding region and T for C at 807 position in the coding region.

The role of carbohydrate in human choriogonadotropin (hCG) action. Effects of N-linked carbohydrate chains from hCG and other glycoproteins on hormonal activity

Deglycosylation of gonadotropins and thyrotropin results in a major loss of hormonal bioactivity, while not impairing receptor-binding activity. However, a direct role of the glycan moieties in hormonal signal transduction has not been demonstrated. The addition of carbohydrate chains together with the deglycosylated hormone does not restore the hormonal activity. In contrast, glycopeptides were found to inhibit human choriogonadotropin (hCG)-stimulated adenylyl cyclase activity and hCG binding to its receptor. An inhibition of hCG-stimulated adenylyl cyclase activity but not hCG binding to receptor by glycopeptides specifically from hCG, has previously been reported as a lectin-like membrane component has been implicated in hCG action. In the present study we have shown that glycopeptides and oligosaccharides prepared from hCG, transferrin, fetuin, alpha 1-acid glycoprotein and ovalbumin inhibit the binding of hCG to its receptor. The inhibition was also observed with a highly purified preparation of the receptor, thus suggesting a lack of involvement of other lectin-like membrane components as previously proposed. We suggest that a lectin-like interaction with the hormone, if any, involves the receptor itself. Adenylyl cyclase activity stimulated by hCG, isoproterenol or forskolin was inhibited by oligosaccharides, indicating a non-specific interaction. Our results suggest that Asn-linked oligosaccharide chains from various glycoproteins perturb hCG-receptor interactions through a putative carbohydrate binding site on the receptor.

Synthesis of cystine peptides 21-25/70-73 and 35-39/56-59 of the beta-subunit of human choriogonadotropin

Syntheses of two asymmetrical cystine peptides with the amino acid residues 21-25/70-73 and 35-39/56-59, based on the linear amino acid sequence and the disulfide bond assignment in the beta-subunit of human choriogonadotropin (hCG-beta), are described. S-trityl and S-acetamidomethyl peptide fragments of each cystine peptide were prepared in solution phase and were subjected to oxidation with I2/MeOH to form the disulfide bridge. The cystine peptides were characterized by their amino acid analyses and fast atom bombardment mass spectrometry. Immunological characterization by several homologous radioimmunoassay systems showed that peptide 21-25/70-73 had significant hCG, hCG-beta, and hLH activities while peptide 35-39/56-59 failed to reveal any immunoreactivity.

Characterization of rat ovarian lutropin receptor. Role of thiol groups in receptor association

Rat ovarian lutropin receptor occurs predominantly as a monomer of an apparent molecular mass of 70 or 80 kDa determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing and reducing conditions, respectively. The receptor contains 0.4% free cysteine and 1.9% cysteine as cystine, determined by amino acid analysis of the S-carboxymethyl receptor prepared before and after reduction. The presence of free thiol groups was further shown by the specific adsorption of the receptor on p-chloromercuribenzoate-agarose and its susceptibility to 3H labeling with [3H]N-ethylmaleimide or [3H]iodoacetic acid. The receptor readily undergoes association into homo-oligomers. Evidence suggests that the association was caused by the intermolecular oxidation of the free -SH groups to form disulfide bonds. The aggregation could be induced by H2O2 or molecular O2 and was inhibited by sulfhydryl protecting agents such as N-ethylmaleimide, iodoacetic acid, dithiothreitol, cysteine, and Zn(II). The oligomers could be dissociated by reduction into a monomer. 125I-Labeling of the S-carboxymethyl- or N-ethylmaleyl receptor gave a single band of molecular mass 70 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Furthermore, S-alkylation of the receptor did not affect its binding to the ligand. On reduction, however, it lost its ability to bind to the ligand, but the reduced receptor retained its ability to bind to a specific polyclonal rabbit antireceptor antibody indicating the separation of the ligand and antibody binding sites. Endoproteinase Glu-C cleaved the receptor at a single glutamyl residue to give two components, 46 and 36 kDa. The 36-kDa component was extracellularly located since it contained the carbohydrate. On deglycosylation with endoglycosidase F, it yielded two components, 27 and 25 kDa. The deglycosylation of the reduced intact receptor (80 kDa) with endoglycosidase F occurred in two steps giving 73- and 64-kDa polypeptides, indicating the presence of about 20% carbohydrate contained in two or more N-linked chains.

A chemical method for the deglycosylation of proteins

A simple and rapid chemical method for the deglycosylation of glycoproteins has been developed. The method involves the incubation of protein with trifluoromethanesulfonic acid at 0 degrees C from 0.5 to 2 h followed by the neutralization of the acid with aqueous pyridine at -20 degrees C. The method has been applied effectively to fetuin, ovine submaxillary mucin, ovine lutropin, and human choriogonadotropin. In 1 h almost all of N- and O-linked carbohydrates from ovine lutropin and human choriogonadotropin, with the exception of the linkage N-acetylglucosamine or N-acetylgalactosamine, were removed. Similarly, in 1 h all N-linked carbohydrates, excepting again the linkage sugar, in fetuin were degraded. Longer reaction times up to 2 h completely removed the O-linked carbohydrate chains from fetuin and ovine submaxillary mucin. The deglycosylated hormones thus prepared retained their immunological and biological activities.

Purification and properties of a monoclonal antibody specific to the free beta-subunit of human chorionic gonadotropin (hCG beta) and its use in the isolation of free hCG beta produced by choriocarcinoma cells

The free beta-subunit of hCG is secreted by several tumors and is reported to be different from native hCG beta. We have developed a monoclonal antibody, B158, specific for free hCG beta to facilitate the detection and isolation of tumor-derived free hCG beta in the presence of intact hCG and hCG alpha. B158 belongs to the immunoglobulin G1 subclass, has high affinity for hCG beta (Ka, 1.05 X 10(9) M-1), and can be obtained in large quantities. The sensitivity of this antibody to detect free hCG beta in a RIA is less than 1 ng. B158 has negligible cross-reactivity with hCG, human LH, and other intact glycoprotein hormones and reacts with the free beta-subunits of deglycosylated hCG, human LH, and ovine LH. The antibody completely inhibits the recombination of hCG beta with hCG alpha indicating the antigenic site to be in the subunit interaction region or its vicinity. Comparison of the amino acid sequences of the various cross-reacting and noncross-reacting hormones indicates that the antigenic site may be discontinuous and conformational. B158 was purified to homogeneity from ascites fluid by DEAE-Affi-Gel blue and hCG beta affinity chromatography. Immobilized pure B158 antibody was used to isolate free hCG beta in a homogeneous form and high yield from BeWo choriocarcinoma cell culture supernatants. This free hCG beta has a slightly higher mol wt than standard hCG beta and recombines normally with hCG alpha. BeWo cells appear to produce only one species of free hCG beta.

The rat ovarian lutropin receptor. Purification, hormone binding properties, and subunit composition

The luteinizing hormone/human choriogonadotropin (hCG) receptor from superovulated rat ovary was purified to homogeneity. A novel scheme based on reverse immunoaffinity chromatography using immobilized antibodies to membrane proteins from receptor down-regulated ovary and subsequent two-step affinity purification on hCG-Sepharose was used to isolate homogeneous receptor. The purification method was also compared to an alternate scheme involving lectin affinity chromatography followed by hCG affinity chromatography. The purified receptor obtained by the latter method was heterogeneous and highly aggregated. The hormone binding properties, molecular size, and subunit composition of the purified receptor obtained by either method were identical. The stability of the receptor during and following solubilization was markedly improved by using 20% glycerol. The pure receptor consists of four nonidentical subunits of molecular weight 79,300 (alpha), 66,400 (beta), 55,300 (gamma), and 46,700 (delta) as indicated by polyacrylamide gel electrophoresis under reducing conditions. All receptor subunits generally, but occasionally excepting the alpha-subunit, were specifically labeled with iodinated hCG in membrane and soluble receptor preparations using bifunctional cross-linking agents. Analysis of the cross-linked hormone-receptor complexes under nonreducing conditions showed the molecular mass of the undissociated receptor to be 268,000 daltons. Hormone binding studies demonstrated that the isolated receptor retained all of the specific binding characteristics expected for the luteinizing hormone/hCG receptor. In combination, these results indicate that the functional and structural properties of the receptor were not altered during purification.

Highly specific and sensitive hybridoma antibodies against the alpha-subunit of human glycoprotein hormones

The free alpha-subunit of human CG (hCG-alpha) has been detected in pregnancy as well as in several endocrine and nonendocrine tumors. In order to facilitate the detection of these tumors, we have developed, by hybridoma technology, very sensitive and highly specific antibodies to hCG-alpha, A2D4 and A2-58. Employing these antibodies, assays were developed to detect picogram levels of the free alpha-subunit. These antibodies have negligible cross-reactivity with intact hCG (A2D4, 0.17%; and A2-58, 1.75%). Pituitary hormone standards of human LH, human FSH, and human TSH from NIH showed cross-reactivity with these antibodies. However, the cross-reactivity was found to be due to the contamination of the hormone preparations with alpha-subunit. The antibodies have no effect on the binding of hCG to its receptor. They cross-react to the same extent with the deglycosylated hCG-alpha and alpha-subunits of all other human glycoprotein hormones but do not react with alpha-subunits of glycoprotein hormones from other species. We have purified these antibodies to homogeneity by DEAE Affi-Gel Blue and affinity chromatography. Both these antibodies belong to immunoglobulin M subclass.

Studies on Turbatrix aceti beta-N-acetylglucosaminidase. 1. Purification and physicochemical characterization

N-Acetyl-beta-D-glucosaminidase was purified, from the culture medium of the nematode Turbatrix aceti, to homogeneity, as judged by electrophoresis in polyacrylamide gel and ultracentrifugation. The purification scheme involved the following steps: (i) concentration of the culture medium by ultra-filtration by an Amicon PM-30 membrane; (ii) ammonium sulfate precipitation; (iii) DEAE-Sephadex and (iv) Sephadex G-200 chromatography; and (v) affinity chromatography on succinyldiaminopropyl amino-Sepharose bearing the ligand p-aminophenyl 2-acetamido-2-deoxy-1-thio-beta-D-glucopyranoside. The molecular weight of the enzyme was 112,000 +/- 4800 and 124,000 as determined by polyacrylamide gel electrophoresis and by gel filtration through Sephacryl S-200, respectively. The enzyme showed a pH optimum of 4.8 for N-acetylglucosaminidase and 5.4 for N-acetylgalactosaminidase. The detailed substrate specificity studies were carried out on both synthetic and natural oligosaccharides and glycopeptides. The chitin oligosaccharides and asialo-agalacto complex type as well as high mannose-type glycoproteins such as fetuin and ovalbumin, respectively, were good substrates for the enzyme. Substrate analogs in which the oxygen atom of the acetamido group was replaced by sulfur atom proved to be poor substrates.

Studies on Turbatrix aceti beta-N-acetylglucosaminidase. 2. Kinetic studies on the active site

The purified beta-N-acetylglucosaminidase isolated from Turbatrix aceti hydrolyzes both p-nitrophenyl 2-acetamido-2-deoxy-beta-D-gluco- and beta-D-galactopyranosides. The enzyme had Km values of 0.28 and 0.23 mM, Vmax values of 104 and 69 mumol min-1 mg protein-1, and activation energies of 11.7 and 9.9 kcal/mol for the two substrates, respectively. Several lines of experimental evidence show that both beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities reside in the same molecule at a single catalytic site. Substrate analogs were synthesized in which the acetamido group of p-nitrophenyl 2-acetamido-2-deoxy-beta-D-gluco- and galactopyranoside, and their 1-thio analogs was modified by replacement of the amido-carbonyl oxygen with sulfur. These substrate analogs competitively inhibited both enzymatic activities. Analysis of the inhibition data indicates that a single catalytic site of the enzyme is responsible for both beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities. Competition kinetics between the two substrates further confirm the presence of a single active site for both activities. The pH dependence of the hydrolysis of p-nitrophenyl 2-acetamido-2-deoxy-beta-D-gluco- and beta-D-galactopyranosides has been determined. pKe1 and pKe2 values of 4.7 and 5.2, determined from the dependence of log Vmax/Km on pH, suggest that two carboxyl groups are involved in the reaction mechanism. The heats of ionization of the groups further confirm the above results.

Biosynthesis of glycoproteins in human placenta: differential labeling of mannose and heterogeneity of oligosaccharide lipid intermediates

The biosynthesis of lipid-linked oligosaccharides has been studied in first trimester human placentas. Tissue was pulsed with [2-3H]mannose, [1-3H]glucosamine, and [1-3H]galactose (for [3H]glucose incorporation). The lipid-linked oligosaccharides (OSL) were purified on DEAE-cellulose. After cleaving the lipid from OSL the oligosaccharides were purified by paper chromatography and borate high-voltage electrophoresis. Four major oligosaccharides with the composition Glc(0-3)Man9GlcNAc2 thus obtained were characterized enzymatically by digestion with endo-beta-N-acetylglucosaminidase H and alpha-mannosidase, and chemically by methylation, acetolysis, and Smith degradation. While identical Glc(1-3)Man9GlcNAc2 oligosaccharides have been isolated from other in vivo systems, the presence of Man9Glc2 is novel for human placenta. Furthermore, Man9GlcNAc2 is present in appreciable amounts in placenta. Second, one mannose in Man9GlcNAc2 had a significantly higher specific radioactivity than the other mannosyl residues of the Glc(0-3)Man9GlcNAc2 oligosaccharides. Third, the differential labeling in Man9GlcNAc2 and our pulse-chase studies indicate that Man9GlcNAc2 is not a major precursor of Glc3Man9GlcNAc2. The data also suggest that the ninth mannose, which has the highest radioactivity, may be incorporated in a different subcellular compartment and may serve as a regulatory step in the biosynthesis of lipid-linked oligosaccharides. A model is proposed which outlines possible multiple pathways of lipid-linked oligosaccharide biosynthesis in human placenta.

Biosynthesis of glycoproteins in human placenta: processing of oligosaccharides

The processing of the high-mannose asparagine-linked oligosaccharides synthesized by first-trimester human placenta has been investigated. Tissue was pulsed for 1 h with [2-3H]mannose and chased for zero, 45, 90, and 180 min in media containing unlabeled mannose. Glycopeptides, prepared by Pronase digestion of the delipidated membrane pellets at each time point, were treated with endo-beta-N-acetylglucosaminidase-H to release the high-mannose asparagine-linked oligosaccharides. The largest major processing intermediate isolated was Glc1Man9GlcNAc, which was converted into Man9GlcNAc, and then into Man8GlcNAc, Man7GlcNAc, Man6GlcNAc, and Man5GlcNAc. There was also a minor pathway in which mannosyl residues were removed prior to the glucose. By carrying out the detailed structural characterization of the individual processing intermediates, it was possible to demonstrate that processing of the Man9GlcNAc to Man5GlcNAc proceeded by the nonrandom removal of the alpha 1,2-linked mannosyl residues. Specifically, of 12 possible sequences of removal of the four alpha 1,2-linked mannosyl residues present in Man9GlcNAc, first-trimester human placenta utilized only two of these in the processing of asparagine-linked oligosaccharides. It is suggested that the limited number of processing pathways reflects a high degree of specificity of these reactions in human placenta.

A specific and sensitive radioimmunoassay for human choriogonadotropin

A specific and sensitive radioimmunoassay for human choriogonadotropin (hCG) has been developed using rabbit antiserum to chemical analogs of beta subunit of human chorionic gonadotropin prepared by controlled reduction and S-alkylation of its disulfide linkages. The assay was highly specific for hCG as the binding of [125I]-hCG to the antibody was not affected by standard human lutropin, by human male serum, postpartum serum from women, serum from post-menopausal women and human menopausal gonadotropin (Pergonal). The assay was highly sensitive, the minimal detection limit in terms of highly purified hCG (L-129, 12500 IU/mg) being 1 ng/ml or 0.2 ng/tube (or 12 mlU/ml in terms of WHO 2nd international reference preparation of hCG). Using this assay we were unable to detect any immunoreactive hCG in human tissues like lung, liver and colon. The high specificity, sensitivity, accuracy and reproducibility of the assay make this a highly desirable radioimmunoassay for human choriogonadotropin.

Biosynthesis of lutropin in ovine pituitary slices: incorporation of [35S]sulfate in carbohydrate units

Sulfate incorporation into carbohydrate of lutropin (LH) has been studied in sheep pituitary slices using H2(35)SO4. Labeled ovine LH was purified to homogeneity by Sephadex G-100 and carboxymethyl-Sephadex chromatography from both the incubation medium and tissue extract. Autoradiography of the gel showed only two protein bands which comigrated with the alpha and beta subunits of ovine LH in both the purified ovine LH and the immunoprecipitate obtained with LH-specific rabbit antiserum. Furthermore, [35S]sulfate was also incorporated into several other proteins in addition to LH. The location of 35SO2-(4) in the oligosaccharides of ovine LH was evidenced by its presence in the glycopeptides obtained by exhaustive Pronase digestion. The location and the point of attachment of sulfate in the carbohydrate unit were established by the isolation of 4-O-[35S]sulfo-N-acetylhexosaminyl-glycerols and 4-O-[35S] sulfo-N-acetylglucosaminitol from the Smith degradation products and by the release of 35SO2-(4) by chondro-4-sulfatase. Thus, the present line of experimentation indicates the presence of sulfate on both the terminal N-acetylglucosamine and N-acetylgalactosamine in the oligosaccharide chains of the labeled ovine LH.

Structure of carbohydrate units of ovine luteinizing hormone

The detailed structures of the three asparagine-linked carbohydrate units of ovine lutropin subunits alpha and beta (oLH-alpha and oLH-beta) have been determined by carrying out the structural analysis on the three glycopeptides alpha GP-1, alpha GP-2, and beta GP-3, and the oligosaccharide obtained by alkaline sodium borohydride treatment of oLH and the individual subunits. Based on the results of methylation, periodate oxidation, deamination, acetolysis, and enzymatic studies with exoglycosidases, the following structure is proposed for the carbohydrate units of oLH. Methylation studies indicated that the 3 N-acetylglucosaminyl residues were substituted at 1-, 1,4-, and 1,4,6-positions. Two of the three mannosyl residues were 1,2-linked and 3rd mannosyl residue was 1,3,6-linked. Fucose and galactose were terminally located and N-acetylgalactosamine was substituted at C-4. Periodate oxidation studies were consistent with the methylation data. The isolation of (formula, see text) 2,5-anhydromannose by the deamination of the oLH oligosaccharide established the branched structure for the mannosyl residues as well as the linkage of the trimannose unit to N-acetylglucosamine. The nonreducing terminal position of N-acetylgalactosamine was indicated by the formation of N-acetylgalactosaminyl glyceraldehyde on Smith degradation of oLH. The presence of a substituent "X" on N-acetylgalactosamine was established by the isolation of X-2,5-anhydrotalitol from the deamination products of oLH oligosaccharide. X was found to be an acid-labile substituent and was identified as a sulfate ester. Last but not least, since oLH oligosaccharide, obtained by hydrolysis of the hormone with NaOH + NaBH4, contained N-acetylglucosaminitol at the reducing end, the carbohydrate must be linked to the protein through N-acetylglucosamine.