Bacterial expression of human chorionic gonadotropin alpha subunit: studies on refolding, dimer assembly and interaction with two different beta subunits

Cystamine restores GSTA3 levels in Vanin-1 null mice

Free cysteamine levels in mouse tissues have been strictly correlated to the presence of membrane-bound pantetheinase activity encoded by Vanin-1. Vanin-1 is involved in many biological processes in mouse, from thymus homing to sexual development. Vanin-1 -/- mice are fertile and grow and develop normally; they better control inflammation and most of the knockout effects were rescued by cystamine treatment. Gene structure analysis showed the presence of an oxidative stimuli-responsive ARE-like sequence in the promoter. In this paper we investigate antioxidant-detoxifying enzymatic activities at the tissue level, comparing Vanin-1 -/- and wild-type mice. In Vanin-1 null animals we pointed out a decrease in the Se-independent glutathione peroxidase activity. The decrease in enzymatic activity appeared to be correlated to an impairment of GST isoenzyme levels. In particular a significant drop in GSTA3 together with a minor decrement in GSTM1 and an increase in GSTP1 levels was detected in Vanin-1 -/- livers. Cystamine administration to Vanin-1 -/- mice restored specifically GSTA3 levels and the corresponding enzymatic activity without influencing protein expression. A possible role of cystamine on protein stability/folding can be postulated.

High-level expression of biologically active glycoprotein hormones in Pichia pastoris strains--selection of strain GS115, and not X-33, for the production of biologically active N-glycosylated 15N-labeled phCG

The methylotrophic yeast Pichia pastoris is widely used for the production of recombinant glycoproteins. With the aim to generate biologically active ¹⁵N-labeled glycohormones for conformational studies focused on the unravelling of the NMR structures in solution, the P. pastoris strains GS115 and X-33 were explored for the expression of human chorionic gonadotropin (phCG) and human follicle-stimulating hormone (phFSH). In agreement with recent investigations on the N-glycosylation of phCG, produced in P. pastoris GS115, using ammonia/glycerol-methanol as nitrogen/carbon sources, the N-glycosylation pattern of phCG, synthesized using NH₄Cl/glucose–glycerol–methanol, comprised neutral and charged, phosphorylated high-mannose-type N-glycans (Man_8–15GlcNAc₂). However, the changed culturing protocol led to much higher amounts of glycoprotein material, which is of importance for an economical realistic approach of the aimed NMR research. In the context of these studies, attention was also paid to the site specific N-glycosylation in phCG produced in P. pastoris GS115. In contrast to the rather simple N-glycosylation pattern of phCG expressed in the GS115 strain, phCG and phFSH expressed in the X-33 strain revealed, besides neutral high-mannose-type N-glycans, also high concentrations of neutral hypermannose-type N-glycans (Man_up-to-30GlcNAc₂). The latter finding made the X-33 strain not very suitable for generating ¹⁵N-labeled material. Therefore, ¹⁵N-phCG was expressed in the GS115 strain using the new optimized protocol. The ¹⁵N-enrichment was evaluated by ¹⁵N-HSQC NMR spectroscopy and GLC-EI/MS. Circular dichroism studies indicated that ¹⁵N-phCG/GS115 had the same folding as urinary hCG. Furthermore, ¹⁵N-phCG/GS115 was found to be similar to the unlabeled protein in every respect as judged by radioimmunoassay, radioreceptor assays, and in vitro bioassays.

A Single‐Step Chromatographic Method for the Purification of Proteins Devoid of Exposed Histidine Residues

The principle of the immobilized metal affinity chromatography (IMAC) is based on the differences in the affinity of proteins for metal ions bound in a 1:1 complex of iminodiacetic acid (IDA) immobilized on a chromatographic support. A single step purification was carried out for luteinizing hormone (LH) on Cu2+, Zn2+, Ni2+, and Co2+ IDA Sepharose affinity columns. Highly purified LH was obtained with a Cu2+ IDA Sepharose column. SDS-PAGE and Western blot analysis were done to confirm the purity of the hormone. Biological activity has been evaluated by radio-immunoassay. This method was found economically viable and suitable for the recovery of biologically active hormone.

Role of glycosylation in function of follicle-stimulating hormone

The oligosaccharide structures of heterodimeric glycoprotein hormones, such as follicle-stimulating hormone (FSH), have been shown to play an important role in the biosynthesis, secretion, metabolic fate, and regulation of potency of the hormone. The oligosaccharide structures attached to each subunit of the protein seem to exhibit distinct roles in some of these functions. Glycans attached to the alpha-subunit are critical for dimer assembly, integrity, and secretion, as well as for signal transduction; although beta-subunit glycans are also important for dimer assembly and secretion, they play a crucial role in clearance of the dimer from the circulation. Alternative glycosylation on FSH and other glycoprotein hormones not only may affect the metabolic clearance and net in vivo biopotency of the hormone, but also offers the interesting possibility that some glycosylation variants of the hormone may provoke differential or even unique effects at the target cell level. Glycosylation of FSH is regulated by hypothalamic and/or end products from the glands under the control of this hormone. In particular, estrogens regulate terminal sialylation and thus some functional properties of the gonadotropin influenced by sialic acid. Through these extrapituitary inputs, the gonadotroph may regulate not only the amount but also the intensity of the gonadotropin signal to be secreted by the pituitary in a given physiological condition.

Identification of an attenuating region in the bovine follicle-stimulating hormone beta subunit mRNA that decreases its expression in E. coli

Follicle-stimulating hormone (FSH) is one of the key regulators of gonadal function in mammals. Recombinant DNA expression of this hormone has proved to be a difficult task as expression levels are invariably low, irrespective of the expression system employed. In the present study, we have attempted to identify reasons for this low expression using bacterial expression vectors, and we report here the identification of a theoretically predicted hairpin structure in the mRNA corresponding to the N-terminal portion of the mature coding portion of bFSHbeta cDNA that is responsible for attenuating its expression in E. coli. When full-length FSHbeta was expressed using the bacterial expression vector, a very low expression was obtained. However, when fragments of FSHbeta with N-terminal deletions (amino acids 24-110 and 13-110) were expressed using the same expression strategy, a 30- to 40-fold higher expression was observed. This low expression of FSHbeta could be attributed to a hairpin structure present in the first 12 codons of mature FSHbeta mRNA. Disruption of this structure without changing the amino acid sequence resulted in a higher level of expression of FSHbeta. The predicted hairpin structure, though away from the transcriptional and translational start site, was able to downregulate the expression of FSHbeta probably by impeding the movement of ribosomes.

Expression of biologically active beta subunit of bovine follicle-stimulating hormone in the methylotrophic yeast Pichia pastoris

Follicle-stimulating hormone (FSH), a pituitary gonadotropin, is a heterodimer composed of an alpha subunit, which is common to all the glycoprotein hormones, noncovalently associated with the hormone-specific beta subunit. The objective of the present study is to develop a recombinant DNA expression system for the beta subunit of FSH that can be applied to study structure-function relationships while producing large quantities of the hormone subunit for immuno-contraceptive, clinical, and veterinary purposes. We report here the expression of biologically active bovine FSH beta (bFSH beta) in the methylotrophic yeast Pichia pastoris. The Pichia-expressed FSH beta (pFSH beta) was secreted into the culture medium and was found to be immunologically very similar to pituitary-derived ovine FSH beta. Replacement of cognate signal peptide with the yeast alpha mating factor signal peptide increased the level of expression from 230 ng/ml (cognate signal peptide) to 4 micrograms/ml (alpha mating factor signal peptide) of the culture supernatant. pFSH beta His.tag (pFSH beta with six histidine residues at the C terminus) was purified to apparent homogeneity using one-step nickel affinity chromatography. The molecular weight of purified pFSH beta His.tag was approximately 22,000, which was slightly higher than that of the pituitary-derived ovine FSH beta. pFSH beta His.tag could assemble with the alpha subunit to yield a heterodimer capable of binding to the FSH receptors and also elicit biological response. These data show that pFSH beta His.tag is properly folded and biologically active.