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Bousfield GR, Harvey DJ. Follicle-Stimulating Hormone Glycobiology. Endocrinology 2019; 160:1515-1535. [PMID: 31127275 PMCID: PMC6534497 DOI: 10.1210/en.2019-00001] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Accepted: 04/16/2019] [Indexed: 01/13/2023]
Abstract
FSH glycosylation varies in two functionally important aspects: microheterogeneity, resulting from oligosaccharide structure variation, and macroheterogeneity, arising from partial FSHβ subunit glycosylation. Although advances in mass spectrometry permit extensive characterization of FSH glycan populations, microheterogeneity remains difficult to illustrate, and comparisons between different studies are challenging because no standard format exists for rendering oligosaccharide structures. FSH microheterogeneity is illustrated using a consistent glycan diagram format to illustrate the large array of structures associated with one hormone. This is extended to commercially available recombinant FSH preparations, which exhibit greatly reduced microheterogeneity at three of four glycosylation sites. Macroheterogeneity is demonstrated by electrophoretic mobility shifts due to the absence of FSHβ glycans that can be assessed by Western blotting of immunopurified FSH. Initially, macroheterogeneity was hoped to matter more than microheterogeneity. However, it now appears that both forms of carbohydrate heterogeneity have to be taken into consideration. FSH glycosylation can reduce its apparent affinity for its cognate receptor by delaying initial interaction with the receptor and limiting access to all of the available binding sites. This is followed by impaired cellular signaling responses that may be related to reduced receptor occupancy or biased signaling. To resolve these alternatives, well-characterized FSH glycoform preparations are necessary.
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Affiliation(s)
- George R Bousfield
- Department of Biological Sciences, Wichita State University, Wichita, Kansas
- Correspondence: George R. Bousfield, PhD, Department of Biological Sciences, Wichita State University, 1845 Fairmount Street, Wichita, Kansas 67260. E-mail: ; or David J. Harvey, DSc, Target Discovery Institute, Nuffield Department of Medicine, University of Oxford. Roosevelt Drive, Oxford OX3 7FZ, United Kingdom. E-mail:
| | - David J Harvey
- Target Discovery Institute, Nuffield Department of Medicine, Oxford University, Oxford, United Kingdom
- Correspondence: George R. Bousfield, PhD, Department of Biological Sciences, Wichita State University, 1845 Fairmount Street, Wichita, Kansas 67260. E-mail: ; or David J. Harvey, DSc, Target Discovery Institute, Nuffield Department of Medicine, University of Oxford. Roosevelt Drive, Oxford OX3 7FZ, United Kingdom. E-mail:
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Jiang X, Dias JA, He X. Structural biology of glycoprotein hormones and their receptors: insights to signaling. Mol Cell Endocrinol 2014; 382:424-451. [PMID: 24001578 DOI: 10.1016/j.mce.2013.08.021] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 08/20/2013] [Accepted: 08/24/2013] [Indexed: 01/18/2023]
Abstract
This article reviews the progress made in the field of glycoprotein hormones (GPH) and their receptors (GPHR) by several groups of structural biologists including ourselves aiming to gain insight into GPH signaling mechanisms. The GPH family consists of four members, with follicle-stimulating hormone (FSH) being the prototypic member. GPH members belong to the cystine-knot growth factor superfamily, and their receptors (GPHR), possessing unusually large N-terminal ectodomains, belong to the G-protein coupled receptor Family A. GPHR ectodomains can be divided into two subdomains: a high-affinity hormone binding subdomain primarily centered on the N-terminus, and a second subdomain that is located on the C-terminal region of the ectodomain that is involved in signal specificity. The two subdomains unexpectedly form an integral structure comprised of leucine-rich repeats (LRRs). Following the structure determination of hCG in 1994, the field of FSH structural biology has progressively advanced. Initially, the FSH structure was determined in partially glycosylated free form in 2001, followed by a structure of FSH bound to a truncated FSHR ectodomain in 2005, and the structure of FSH bound to the entire ectodomain in 2012. Comparisons of the structures in three forms led a proposal of a two-step monomeric receptor activation mechanism. First, binding of FSH to the FSHR high-affinity hormone-binding subdomain induces a conformational change in the hormone to form a binding pocket that is specific for a sulfated-tyrosine found as sTyr 335 in FSHR. Subsequently, the sTyr is drawn into the newly formed binding pocket, producing a lever effect on a helical pivot whereby the docking sTyr provides as the 'pull & lift' force. The pivot helix is flanked by rigid LRRs and locked by two disulfide bonds on both sides: the hormone-binding subdomain on one side and the last short loop before the first transmembrane helix on the other side. The lift of the sTyr loop frees the tethered extracellular loops of the 7TM domain, thereby releasing a putative inhibitory influence of the ectodomain, ultimately leading to the activating conformation of the 7TM domain. Moreover, the data lead us to propose that FSHR exists as a trimer and to present an FSHR activation mechanism consistent with the observed trimeric crystal form. A trimeric receptor provides resolution of the enigmatic, but important, biological roles played by GPH residues that are removed from the primary FSH-binding site, as well as several important GPCR phenomena, including negative cooperativity and asymmetric activation. Further reflection pursuant to this review process revealed additional novel structural characteristics such as the identification of a 'seat' sequence in GPH. Together with the 'seatbelt', the 'seat' enables a common heteodimeric mode of association of the common α subunit non-covalently and non-specifically with each of the three different β subunits. Moreover, it was possible to establish a dimensional order that can be used to estimate LRR curvatures. A potential binding pocket for small molecular allosteric modulators in the FSHR 7TM domain has also been identified.
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Affiliation(s)
- Xuliang Jiang
- EMD Serono Research & Development Institute, Billerica, MA 01821, United States.
| | - James A Dias
- Department of Biomedical Sciences, School of Public Health, University at Albany-SUNY, Albany, NY 12222, United States
| | - Xiaolin He
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, United States
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Mishra AK, Mahale SD, Iyer KS. Mapping the receptor binding regions of human chorionic gonadotropin (hCG) using disulfide peptides of its beta-subunit: possible involvement of the disulfide bonds Cys(9)-Cys(57) and Cys(23)-Cys(72) in receptor binding of the hormone. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2001; 58:17-26. [PMID: 11454166 DOI: 10.1034/j.1399-3011.2001.00866.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone essential for the establishment and maintenance of pregnancy. The alpha- and beta-subunits of hCG are highly cross-linked internally by disulfide bonds which seem to stabilize the tertiary structures required for the noncovalent association of the subunits to generate hormonal activity. The purpose of this study was to delineate the role of the disulfide bonds of hCGbeta in receptor binding of the hormone. Six disulfide peptides incorporating each of the six disulfide bonds of hCGbeta were synthesized and screened, along with their linear counterparts, for their ability to competitively inhibit the binding of [125I] hCG to sheep ovarian corpora luteal LH/CG receptor. Disulfide peptide Cys (9-57) was found to be approximately 4-fold more potent than the most active of its linear counterparts in inhibiting radiolabeled hCG from binding to its receptor. Similarly, disulfide peptide Cys (23-72) exhibited receptor binding inhibition activity, whereas the constituent linear peptides were found to be inactive. The results suggest the involvement of the disulfide bonds Cys(9)-Cys(57) and Cys(23)-Cys(72) of the beta-subunit of hCG in receptor binding of the hormone. This study is the first of its kind to use disulfide peptides rather than linear peptides to map the receptor binding regions of hCG.
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Affiliation(s)
- A K Mishra
- Institute for Research in Reproduction, Mumbai, India
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Ren P, Sairam MR, Yarney TA. Bacterial expression of human chorionic gonadotropin alpha subunit: studies on refolding, dimer assembly and interaction with two different beta subunits. Mol Cell Endocrinol 1995; 113:39-51. [PMID: 8674812 DOI: 10.1016/0303-7207(95)03609-b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Human chorionic gonadotropin (hCG) is a member of a family of heterodimeric glycoprotein hormones that have a common alpha subunit but differ in their hormone-specific beta subunit. The common alpha subunit contains two asparagine (N)-linked oligosaccharides. To study the function of carbohydrates on in vitro refolding of alpha subunit and dimer assembly, we generated recombinant non-glycosylated hCG alpha subunit (rNGl-hCGalpha) from E. coli. The expression vector was constructed by inserting hCGalpha cDNA coding for the mature form in-frame into a pQE-30 vector, which contains a 6 x His sequence immediately before the 5'-end of hCGalpha cDNA for subsequent purification of rNG-hCGalpha. The rNG-hCGalpha expressed in inclusion bodies was efficiently purified by immobilized metal chelate affinity chromatography on Ni-NTA resin. SDS-PAGE, solid-phase binding assay and immunoblotting demonstrated the expression of rNG-hCG. Its alpha molecular weight on SDS-PAGE was 14.7 kDa under reducing conditions and 15 kDa for a monomer accompanied with some higher molecular weight oligomer under non-reducing conditions. Reconstitution of rNG-hCGalpha with native hCGbeta and oFSHbeta occurred in very low yield under standard conditions. However, the oxidation-reduction system cystamine (1.34 mM) and cysteamine (7.3 mM) facilitated both the refolding of rNG-hCGalpha and reconstitution of rNG-hCGalpha with native hCGbeta to regain partially correct conformation. These were revealed by conformationally sensitive antibody and receptor binding assays. Cystamine and cysteamine were more effective in the recombination of rNG-hCGalpha with oFSHbeta as indicated by a 22-36-fold decrease in the amount required to cause a 50% competitive inhibition in radioreceptor assay. They have no effect on assembly of rNG-hCGalpha with oLHbeta. Our results suggest the carbohydrate moieties confer greater conformational flexibility to the backbone of the beta subunit and the relative rigidity of the beta subunit may serve as a conformational template of the alpha subunit. The present approach has made it possible to prepare the non-glycosylated gonadotropin alpha subunit in adequate amounts for further study on their biological and topographical features in complete absence of carbohydrate.
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Affiliation(s)
- P Ren
- Reproduction Research Laboratory, Clinical Research Institute of Montreal, Québec, Canada
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Suganuma N, Matzuk MM, Boime I. Elimination of disulfide bonds affects assembly and secretion of the human chorionic gonadotropin β subunit. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)47301-8] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Matzuk MM, Boime I. Site-specific mutagenesis defines the intracellular role of the asparagine-linked oligosaccharides of chorionic gonadotropin beta subunit. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)37504-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Birken S, Gawinowicz Kolks MA, Amr S, Nisula B, Puett D. Tryptic digestion of the alpha subunit of human choriogonadotropin. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67445-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Hayashizaki Y, Miyai K, Kato K, Matsubara K. Molecular cloning of the human thyrotropin-beta subunit gene. FEBS Lett 1985; 188:394-400. [PMID: 3839756 DOI: 10.1016/0014-5793(85)80409-9] [Citation(s) in RCA: 75] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Genomic DNA fragments that carried a gene for human thyrotropin-beta (hTSH beta) subunit were isolated. Nucleotide sequence analysis of the gene showed that the hTSH beta subunit precursor consists of 138 amino acid residues. There is an N-terminal sequence of 20 amino acids as a signal peptide, followed by 112 amino acids, whose sequence is in agreement with that known for the secretory form of hTSH beta subunit. This is followed by an additional stretch of 6 hydrophobic amino acids, which may be eliminated post-translationally. The coding region is separated by an intron of about 460 bp. Genomic Southern blot hybridization analysis suggested that the hTSH beta gene is a unique single copy gene.
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The beta subunits of glycoprotein hormones. Formation of three-dimensional structure during cell-free biosynthesis of lutropin-beta. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89094-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Strickland TW, Thomason AR, Nilson JH, Pierce JG. The common alpha subunit of bovine glycoprotein hormones: limited formation of native structure by the totally nonglycosylated polypeptide chain. J Cell Biochem 1985; 29:225-37. [PMID: 2416766 DOI: 10.1002/jcb.240290307] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The folding of the bovine glycoprotein hormone alpha subunit, synthesized in bacteria following insertion of the nucleotide sequence coding for this polypeptide, has been studied to determine the effect that a complete lack of carbohydrate has on this process. The bacterially derived alpha polypeptide (bac-alpha), extracted from E. coli in the presence of reductant and denaturant, had an estimated 0.2% native structure as determined by a conformationally sensitive radioimmunoassay. Upon reduction of disulfide bonds and reoxidation in air, the amount of native structure increased about 18-fold. Approximately 2% of the refolded bac-alpha preparation combines with the beta subunit of human chorionic gonadotropin (hCG beta) to form a complex that binds to the gonadotropin receptor and elicits a biological response. Since the correct folding (by immunological criteria) of bac-alpha (ca 3%) is significantly greater than expected from a random formation of disulfide bonds (0.1%), it appears that correct folding of alpha subunit can occur in the complete absence of carbohydrate, though in very low yield. Native bovine lutropin alpha subunit (LH alpha) and chemically deglycosylated LH alpha (which retains two asparagine-linked N-acetyl glucosamine residues per alpha oligosaccharide) were subjected to the same reduction/reoxidation regimen as the bacterially produced alpha subunit. As has been reported previously [Giudice LC, Pierce, JG, J Biol Chem 251: 6392, 1976] intact LH alpha fully regained its native structure. The partially deglycosylated LH alpha also refolds to a native-like structure in high yield as assessed by immunological assays and by its ability to combine with HCG beta to form a biologically active complex. The data show that carbohydrate, while not obligatory for correct folding, greatly facilitates the formation of functional alpha subunit.
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The alpha subunit of pituitary glycoprotein hormones. Formation of three-dimensional structure during cell-free biosynthesis. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(20)81985-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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12
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Enzymatic deglycosylation of the subunits of chorionic gonadotropin. Effects on formation of tertiary structure and biological activity. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33393-3] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Reeve JR, Pierce JG. Disulfide bonds of glycoprotein hormones. Their selective reduction in the beta subunits of bovine lutropin and thyrotropin. INTERNATIONAL JOURNAL OF PEPTIDE AND PROTEIN RESEARCH 1981; 18:79-87. [PMID: 7309370 DOI: 10.1111/j.1399-3011.1981.tb02042.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Pierce JG, Parsons TF. Glycoprotein hormones: similar molecules with different functions. UCLA FORUM IN MEDICAL SCIENCES 1980:99-117. [PMID: 400318 DOI: 10.1016/b978-0-12-643150-6.50014-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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15
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Evidence for conformational differences between precursor and processed forms of thyroid-stimulating hormone beta subunit. J Biol Chem 1979. [DOI: 10.1016/s0021-9258(19)86367-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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