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Hessefort H, Gross A, Seeleithner S, Hessefort M, Kirsch T, Perkams L, Bundgaard KO, Gottwald K, Rau D, Graf CGF, Rozanski E, Weidler S, Unverzagt C. Chemical and Enzymatic Synthesis of Sialylated Glycoforms of Human Erythropoietin. Angew Chem Int Ed Engl 2021; 60:25922-25932. [PMID: 34523784 PMCID: PMC9297946 DOI: 10.1002/anie.202110013] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/31/2021] [Indexed: 01/15/2023]
Abstract
Recombinant human erythropoietin (EPO) is the main therapeutic glycoprotein for the treatment of anemia in cancer and kidney patients. The in‐vivo activity of EPO is carbohydrate‐dependent with the number of sialic acid residues regulating its circulatory half‐life. EPO carries three N‐glycans and thus obtaining pure glycoforms provides a major challenge. We have developed a robust and reproducible chemoenzymatic approach to glycoforms of EPO with and without sialic acids. EPO was assembled by sequential native chemical ligation of two peptide and three glycopeptide segments. The glycopeptides were obtained by pseudoproline‐assisted Lansbury aspartylation. Enzymatic introduction of the sialic acids was readily accomplished at the level of the glycopeptide segments but even more efficiently on the refolded glycoprotein. Biological recognition of the synthetic EPOs was shown by formation of 1:1 complexes with recombinant EPO receptor.
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Affiliation(s)
- Hendrik Hessefort
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Angelina Gross
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Simone Seeleithner
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Markus Hessefort
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Tanja Kirsch
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Lukas Perkams
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Klaus Ole Bundgaard
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Karen Gottwald
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - David Rau
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | | | - Elisabeth Rozanski
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Sascha Weidler
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Carlo Unverzagt
- University of Bayreuth, Bioorganic Chemistry, Universitätsstraße 30, 95447, Bayreuth, Germany
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2
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Hessefort H, Gross A, Seeleithner S, Hessefort M, Kirsch T, Perkams L, Bundgaard KO, Gottwald K, Rau D, Graf CGF, Rozanski E, Weidler S, Unverzagt C. Chemical and Enzymatic Synthesis of Sialylated Glycoforms of Human Erythropoietin. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202110013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Hendrik Hessefort
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Angelina Gross
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Simone Seeleithner
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Markus Hessefort
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Tanja Kirsch
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Lukas Perkams
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Klaus Ole Bundgaard
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Karen Gottwald
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - David Rau
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | | | - Elisabeth Rozanski
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Sascha Weidler
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
| | - Carlo Unverzagt
- University of Bayreuth Bioorganic Chemistry Universitätsstraße 30 95447 Bayreuth Germany
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3
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Hatayama K, Ide T. Engineering of erythropoietin receptor for use as an affinity ligand. Protein Expr Purif 2015; 111:1-8. [DOI: 10.1016/j.pep.2015.03.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 03/06/2015] [Accepted: 03/10/2015] [Indexed: 10/23/2022]
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4
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Vascular growth factors in neuropsychiatry. Cell Mol Life Sci 2013; 70:1739-52. [PMID: 23475069 DOI: 10.1007/s00018-013-1281-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 01/28/2013] [Accepted: 01/28/2013] [Indexed: 01/03/2023]
Abstract
Recent advances in understanding the cellular and molecular basis of psychiatric illnesses have shed light on the important role played by trophic factors in modulating functional parameters associated with disease causality and drug action. Disease mechanisms are now thought to involve multiple cell types, including neurons and endothelial cells. These functionally distinct but interactively coupled cell types engage in cellular cross talk via shared and common signaling molecules. Dysregulation in their cellular signaling pathways influences brain function and alters behavioral performance. Multifunctional trophic factors such as VEGF and EPO that possess both neurotrophic and angiogenic actions are of particular interest due to their ability to rescue structural and plasticity deficits in neurons and vasculature. Obtaining insight into the behavioral, cellular and molecular actions of multi-functional trophic factors has the potential to open new and transformative therapeutic approaches.
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5
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Lacy SE, DeVries PJ, Xie N, Fung E, Lesniewski RR, Reilly EB. The potency of erythropoietin-mimic antibodies correlates inversely with affinity. THE JOURNAL OF IMMUNOLOGY 2008; 181:1282-7. [PMID: 18606682 DOI: 10.4049/jimmunol.181.2.1282] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Preclinical animal studies have shown that Ab12.6, an agonistic human Ab targeting the erythropoietin receptor (EPOR), exhibits several potential dosing and safety features that make it an attractive clinical candidate for the treatment of anemia. Ab12.6 was derived by yeast display affinity maturation of parental Ab12, a strategy initially intended to improve off-rate and affinity for EPOR, thereby enhancing erythropoietic activity. Analysis of full-length IgGs derived from yeast clones identified sequences within Ab12 CDRH2 that independently influenced both affinity and potency. The Ab12.6 derivative displayed improved in vitro potency and in vivo efficacy, although its binding affinity to the EPOR was lower than that of the parent Ab12. Additional Ab12 derivatives also exhibited an inverse correlation between affinity and potency. These results suggest that for this class of agonistic Abs, faster off-rates may permit continuous receptor stimulation and more efficient erythropoiesis.
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Affiliation(s)
- Susan E Lacy
- Global Pharmaceutical Research and Development, Abbott Bioresearch Center, Worcester, MA 01605, USA
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6
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Liu Z, Stoll VS, Devries PJ, Jakob CG, Xie N, Simmer RL, Lacy SE, Egan DA, Harlan JE, Lesniewski RR, Reilly EB. A potent erythropoietin-mimicking human antibody interacts through a novel binding site. Blood 2007; 110:2408-13. [PMID: 17620453 DOI: 10.1182/blood-2007-04-083998] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recombinant human erythropoietin (rHu-EPO) is used to treat anemia by activating the erythropoietin receptor (EPOR) in erythroid progenitor cells, leading to proliferation and differentiation into mature red blood cells. To allow less frequent dosing, a hyperglycosylated version of EPO has been developed with a longer half-life. In principle, an agonistic antibody targeting EPOR would offer an even longer half-life, support robust monthly dosing, and, unlike EPO products, reduce the risk of pure red cell aplasia. The efficiency of signaling and corresponding potency of previously reported antibody mimics are generally suboptimal compared with EPO and not suitable for clinical use. Here we describe a potent, fully human, agonistic antibody (ABT007) targeting EPOR that supports potent, more sustained, and less pulsatile elevation of hematocrit in a human EPOR–expressing transgenic mouse model compared with standard doses of rHu-EPO while requiring less frequent dosing. Resolution of the crystal structure of the EPOR extracellular domain (ECD) complexed to the ABT007 Fab fragment, determined at 0.32 nm, identifies a binding site that is consistent with a novel mechanism of receptor activation based on a unique antibody-imposed conformational change. These results demonstrate that a symmetric molecule can serve as a potent activator of the EPOR.
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MESH Headings
- Animals
- Antibodies/immunology
- Binding Sites
- Cell Line
- Crystallography, X-Ray
- Erythropoiesis
- Erythropoietin/metabolism
- Hematocrit
- Humans
- Mice
- Mice, Knockout
- Models, Molecular
- Molecular Mimicry
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Receptors, Erythropoietin/chemistry
- Receptors, Erythropoietin/deficiency
- Receptors, Erythropoietin/genetics
- Receptors, Erythropoietin/metabolism
- Structural Homology, Protein
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Affiliation(s)
- Zhihong Liu
- Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064-6199, USA
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7
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Weerasinghe CU, Learmonth GS, Gilkerson JR, Foote CE, Wellington JE, Whalley JM. Equine herpesvirus 1 glycoprotein D expressed in E. coli provides partial protection against equine herpesvirus infection in mice and elicits virus-neutralizing antibodies in the horse. Vet Immunol Immunopathol 2006; 111:59-66. [PMID: 16473414 DOI: 10.1016/j.vetimm.2006.01.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The envelope glycoprotein D of EHV-1 (EHV-1 gD) is essential for virus infectivity and entry of virus into cells and is a potent inducer of virus-neutralizing antibody. In this study, truncated EHV-1 gD (gDt) was expressed with a C-terminal hexahistidine tag in E. coli using a pET vector. Western blot analysis using an anti-gD monoclonal antibody demonstrated the presence of gDt bands at 37.5, 36, 29.5 and 28 kDa. The immunogenicity and protective efficacy of partially purified gDt was compared with gD expressed in insect cells by a recombinant baculovirus (Bac gD) using a BALB/c mouse model of EHV-1 respiratory infection. The proteins were also compared in a prime-boost protocol following an initial inoculation with gD DNA. gDt elicited similar levels of gD-specific antibody and neutralizing antibody compared with Bac gD and also provided a similar level of protection against EHV-1 challenge in mice. Inoculation of horses with gDt elicited EHV-1 gD-specific antibodies including virus-neutralizing antibody, suggesting that despite the lack of glycosylation, E. coli may be a useful vehicle for large scale production of EHV-1 gD for vaccine studies.
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Affiliation(s)
- C U Weerasinghe
- Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia
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8
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Khushoo A, Pal Y, Singh BN, Mukherjee KJ. Extracellular expression and single step purification of recombinant Escherichia coli L-asparaginase II. Protein Expr Purif 2005; 38:29-36. [PMID: 15477079 DOI: 10.1016/j.pep.2004.07.009] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2004] [Revised: 07/14/2004] [Indexed: 11/27/2022]
Abstract
L-Asparaginase (isozyme II) from Escherichia coli is an important therapeutic enzyme used in the treatment of leukemia. Extracellular expression of recombinant asparaginase was obtained by fusing the gene coding for asparaginase to an efficient pelB leader sequence and an N-terminal 6x histidine tag cloned under the T7lac promoter. Media composition and the induction strategy had a major influence on the specificity and efficiency of secretion of recombinant asparaginase. Induction of the cells with 0.1 mM IPTG at late log phase of growth in TB media resulted in fourfold higher extracellular activity in comparison to growing the cells in LB media followed by induction during the mid log phase. Using an optimized expression strategy a yield of 20,950 UI/L of recombinant asparaginase was obtained from the extracellular medium. The recombinant protein was purified from the culture supernatant in a single step using Ni-NTA affinity chromatography which gave an overall yield of 95 mg/L of purified protein, with a recovery of 86%. This is approximately 8-fold higher to the previously reported data in literature. The fluorescence spectra, analytical size exclusion chromatography, and the specific activity of the purified protein were observed to be similar to the native protein which demonstrated that the protein had folded properly and was present in its active tetramer form in the culture supernatant.
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Affiliation(s)
- Amardeep Khushoo
- Centre for Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India
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9
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Sandee D, Tungpradabkul S, Kurokawa Y, Fukui K, Takagi M. Combination of Dsb coexpression and an addition of sorbitol markedly enhanced soluble expression of single-chain Fv inEscherichia coli. Biotechnol Bioeng 2005; 91:418-24. [PMID: 15937881 DOI: 10.1002/bit.20524] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Many eukaryotic proteins have been produced successfully in Escherichia coli. However, not every gene can be expressed efficiently in this organism. Most proteins, especially those with multiple disulfide bonds, have been shown to form insoluble protein or inclusion body in E. coli. An inactive form of protein would require an in vitro refolding step to regain biological functions. In this study, we described the system for soluble expression of a single-chain variable fragment (scFv) against hepatocellular carcinoma (Hep27scFv) by coexpressing Dsb protein and enhancing with medium additives. The results revealed that overexpression of DsbABCD protein showed marked effect on the soluble production of Hep27scFv, presumably facilitating correct folding. The optimal condition for soluble scFv expression could be obtained by adding 0.5M sorbitol to the culture medium. The competitive enzyme-linked immunosorbent assay (ELISA) indicated that soluble scFv expressed by our method retains binding activity toward the same epitope on a hepatocellular carcinoma cell line (HCC-S102) recognized by intact antibody (Ab) (Hep27 Mab). Here, we report an effective method for soluble expression of scFv in E. coli by the Dsb coexpression system with the addition of sorbitol medium additive. This method might be applicable for high-yield soluble expression of proteins with multiple disulfide bonds.
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Affiliation(s)
- Duanpen Sandee
- Department of Biotechnology, Graduate school of Engineering, Osaka University, Suita, Osaka, Japan
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10
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Arakawa T, Li T, Narhi LO. Recombinant production of native proteins from Escherichia coli. PHARMACEUTICAL BIOTECHNOLOGY 2002; 13:27-60. [PMID: 11987753 DOI: 10.1007/978-1-4615-0557-0_2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Tsutomu Arakawa
- Alliance Protein Laboratories, 3957 Corte Cancion, Thousand Oaks, CA 91360, USA
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11
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Biazzo DE, Motamedi H, Mark DF, Qureshi SA. A high-throughput assay to identify compounds that can induce dimerization of the erythropoietin receptor. Anal Biochem 2000; 278:39-45. [PMID: 10640351 DOI: 10.1006/abio.1999.4408] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Erythropoietin induces dimerization of the erythropoietin receptor on the surface of erythroid progenitor cells, promoting the differentiation of these cells into mature red blood cells. To facilitate screening of large chemical collections for identification of compounds that can dimerize erythropoietin receptor, we have developed a novel, high-throughput in vitro assay to detect compounds that can cause dimerization of the erythropoietin receptor in solution. To develop this assay, amino acid sequences corresponding to the extracellular domain of erythropoietin receptor were expressed in Escherichia coli as erythropoietin-binding protein (rEBP). A modified version of this protein ((33)P-rEBP) containing a protein kinase A substrate site incorporated into the rEBP was also expressed in E. coli and labeled in vitro using protein kinase A and ¿gamma-(33)PATP. An erythropoietin mimetic peptide (EMP-1), that induces dimerization of rEBP in solution was used to demonstrate dimerization of (33)P-rEBP and rEBP in a 96-well microtiter plate format. EMP-1 induced dimerization of rEBP in this assay with an EC(50) of approximately 245 nM and had a maximal effect at 0.5-2 microM and required the presence of rEBP immobilized on the plate capable of binding EMP-1. EMP-1-induced dimerization of (33)P-rEBP and rEBP was reversed by excess unlabeled rEBP and was not masked by complex mixtures such as whole cell fungal extracts. These data demonstrate the ability of (33)P-rEBP to dimerize with rEBP in vitro in a format that is fully compatible with high-throughput screening.
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Affiliation(s)
- D E Biazzo
- Merck Research Laboratories, Rahway, New Jersey 07065-0900, USA
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12
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Qureshi SA, Kim RM, Konteatis Z, Biazzo DE, Motamedi H, Rodrigues R, Boice JA, Calaycay JR, Bednarek MA, Griffin P, Gao YD, Chapman K, Mark DF. Mimicry of erythropoietin by a nonpeptide molecule. Proc Natl Acad Sci U S A 1999; 96:12156-61. [PMID: 10518592 PMCID: PMC18428 DOI: 10.1073/pnas.96.21.12156] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Erythropoietin (EPO) controls the proliferation and differentiation of erythroid progenitor cells into red blood cells. EPO induces these effects by dimerization of the EPO receptors (EPOR) present on these cells. To discover nonpeptide molecules capable of mimicking the effects of EPO, we identified a small molecule capable of binding to one chain of EPOR and used it to synthesize molecules capable of inducing dimerization of the EPOR. We first identified compound 1 (N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester) by screening the in-house chemical collection for inhibitors of EPO binding to human EPOR and then prepared compound 5, which contains eight copies of compound 1 held together by a central core. Although both compounds inhibited EPO binding of EPOR, only compound 5 induced dimerization of soluble EPOR. Binding of EPO to its receptor in cells results in activation of many intracellular signaling molecules, including transcription factors like signal transducer and activator of transcription (STAT) proteins, leading to growth and differentiation of these cells. Consistent with its ability to induce dimerization of EPOR in solution, compound 5 exhibited much of the same biological activities as EPO, such as (i) the activation of a STAT-dependent luciferase reporter gene in BAF3 cells expressing human EPOR, (ii) supporting the proliferation of several tumor cell lines expressing the human or mouse EPOR, and (iii) the in vitro differentiation of human progenitor cells into colonies of erythrocytic lineage. These data demonstrate that a nonpeptide molecule is capable of inducing EPOR dimerization and mimicking the biological activities of EPO.
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Affiliation(s)
- S A Qureshi
- Merck Research Laboratories, Rahway, NJ 07065, USA.
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13
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Caldwell GW, McDonnell PA, Masucci JA, Johnson DL, Jolliffe LK. Using affinity capillary electrophoresis to study the interaction of the extracellular binding domain of erythropoietin receptor with peptides. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 1999; 40:17-25. [PMID: 10481948 DOI: 10.1016/s0165-022x(99)00011-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have shown that affinity capillary electrophoresis (ACE) can be utilized to screen peptides that bind to the extracellular binding domain of the erythropoietin receptor (EBP). The comparison of the cyclic peptides GGTYSCHFGPLTWVCKPQGG (EMP1) GGTYSCHFGPLTAVCKPQGG (EMP13), and LGRKYSCHFGPLTWVCQPAKKD (EMP37) with the linear peptides HFGPLTWV (EMP26) and FMRF as ACE buffer additives were investigated. When EMP1 and EMP37 were the buffer additives, an abrupt change in the electrophoretic mobility of EBP was observed in the electropherogram. When EMP13, EMP26, and FMRF were examined under identical ACE conditions as EMP1 and EMP37, no significant change in the electrophoretic mobility of EBP was observed. These results correlate well with previously reported IC50 competitive binding data; that is, EMP1 and EMP37 bind to EBP while EMP13 and EMP26 bind very weakly. These observations strongly infer that peptide.EBP dimerization were induced by EMP1, and EMP37 but not by EMP13, EMP26 or FMRF. This ACE method provides a rapid tool for the detection of small peptides or drugs that bind to EBP.
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Affiliation(s)
- G W Caldwell
- The R.W. Johnson Pharmaceutical Research Institute, Spring House, PA, USA.
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14
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Zhan H, Liu B, Reid SW, Aoki KH, Li C, Syed RS, Karkaria C, Koe G, Sitney K, Hayenga K, Mistry F, Savel L, Dreyer M, Katz BA, Schreurs J, Matthews DJ, Cheetham JC, Egrie J, Giebel LB, Stroud RM. Engineering a soluble extracellular erythropoietin receptor (EPObp) in Pichia pastoris to eliminate microheterogeneity, and its complex with erythropoietin. PROTEIN ENGINEERING 1999; 12:505-13. [PMID: 10388848 DOI: 10.1093/protein/12.6.505] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The extracellular ligand-binding domain (EPObp) of the human EPO receptor (EPOR) was expressed both in CHO (Chinese Hamster Ovary) cells and in Pichia pastoris. The CHO and yeast expressed receptors showed identical affinity for EPO binding. Expression levels in P. pastoris were significantly higher, favoring its use as an expression and scale-up production system. Incubation of EPO with a fourfold molar excess of receptor at high protein concentrations yielded stable EPO-EPObp complexes. Quantification of EPO and EPObp in the complex yielded a molar ratio of one EPO molecule to two receptor molecules. Residues that are responsible for EPOR glycosylation and isomerization in Pichia were identified and eliminated by site-specific mutagenesis. A thiol modification was identified and a method was developed to remove the modified species from EPObp. EPObp was complexed with erythropoietin (EPO) and purified. The complex crystallized in two crystal forms that diffracted to 2.8 and 1.9 A respectively. (Form 1 and form 2 crystals were independently obtained at AxyS Pharmaceuticals, Inc. and Amgen, Inc. respectively.) Both contained one complex per asymmetric unit with a stoichiometry of two EPObps to one EPO.
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Affiliation(s)
- H Zhan
- Axys Pharmaceuticals, Inc., 180 Kimball Way, San Francisco, CA 94080, USA
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15
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Middleton SA, Barbone FP, Johnson DL, Thurmond RL, You Y, McMahon FJ, Jin R, Livnah O, Tullai J, Farrell FX, Goldsmith MA, Wilson IA, Jolliffe LK. Shared and unique determinants of the erythropoietin (EPO) receptor are important for binding EPO and EPO mimetic peptide. J Biol Chem 1999; 274:14163-9. [PMID: 10318834 DOI: 10.1074/jbc.274.20.14163] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have shown previously that Phe93 in the extracellular domain of the erythropoietin (EPO) receptor (EPOR) is crucial for binding EPO. Substitution of Phe93 with alanine resulted in a dramatic decrease in EPO binding to the Escherichia coli-expressed extracellular domain of the EPOR (EPO-binding protein or EBP) and no detectable binding to full-length mutant receptor expressed in COS cells. Remarkably, Phe93 forms extensive contacts with a peptide ligand in the crystal structure of the EBP bound to an EPO-mimetic peptide (EMP1), suggesting that Phe93 is also important for EMP1 binding. We used alanine substitution of EBP residues that contact EMP1 in the crystal structure to investigate the function of these residues in both EMP1 and EPO binding. The three largest hydrophobic contacts at Phe93, Met150, and Phe205 and a hydrogen bonding interaction at Thr151 were examined. Our results indicate that Phe93 and Phe205 are important for both EPO and EMP1 binding, Met150 is not important for EPO binding but is critical for EMP1 binding, and Thr151 is not important for binding either ligand. Thus, Phe93 and Phe205 are important binding determinants for both EPO and EMP1, even though these ligands share no sequence or structural homology, suggesting that these residues may represent a minimum epitope on the EPOR for productive ligand binding.
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Affiliation(s)
- S A Middleton
- R. W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey 08869, USA.
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16
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Ahaded A, Winchenne JJ, Cartron JP, Lambin P, Lopez C. The extracellular domain of the human erythropoietin receptor: expression as a fusion protein in Escherichia coli, purification, and biological properties. Prep Biochem Biotechnol 1999; 29:163-76. [PMID: 10231895 DOI: 10.1080/10826069908544888] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
We developed an efficient production system of the soluble extracellular domain of the human erythropoietin receptor (sEPO-R) and characterized the binding of erythropoietin (EPO) with the purified recombinant protein. The sEPO-R, fused to the maltose binding protein (MBP), was expressed as a soluble protein in the periplasm of Escherichia coli (E. coli) and did not accumulate in inclusion bodies. After lysis of the bacteria by an osmotic shock, the fusion protein was purified by affinity chromatography on amylose followed by size exclusion chromatography (SEC). Specific binding of 125I-labelled EPO to the sEPO-R was demonstrated by competitive and saturation binding assays. A single affinity class (Kd = 0.25 nM) of the binding site was evident by Scatchard analysis. This value is similar to the Kd observed between EPO and the EPO-R of high affinity present on human erythroid progenitors. The complex has a molecular size corresponding to a 1:1 complex of EPO and the fusion protein.
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Affiliation(s)
- A Ahaded
- Institut National de la Transfusion Sanguine (INTS), Paris, France
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17
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Livnah O, Stura EA, Middleton SA, Johnson DL, Jolliffe LK, Wilson IA. Crystallographic evidence for preformed dimers of erythropoietin receptor before ligand activation. Science 1999; 283:987-90. [PMID: 9974392 DOI: 10.1126/science.283.5404.987] [Citation(s) in RCA: 460] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Erythropoietin receptor (EPOR) is thought to be activated by ligand-induced homodimerization. However, structures of agonist and antagonist peptide complexes of EPOR, as well as an EPO-EPOR complex, have shown that the actual dimer configuration is critical for the biological response and signal efficiency. The crystal structure of the extracellular domain of EPOR in its unliganded form at 2.4 angstrom resolution has revealed a dimer in which the individual membrane-spanning and intracellular domains would be too far apart to permit phosphorylation by JAK2. This unliganded EPOR dimer is formed from self-association of the same key binding site residues that interact with EPO-mimetic peptide and EPO ligands. This model for a preformed dimer on the cell surface provides insights into the organization, activation, and plasticity of recognition of hematopoietic cell surface receptors.
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Affiliation(s)
- O Livnah
- Department of Molecular Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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18
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Livnah O, Johnson DL, Stura EA, Farrell FX, Barbone FP, You Y, Liu KD, Goldsmith MA, He W, Krause CD, Pestka S, Jolliffe LK, Wilson IA. An antagonist peptide-EPO receptor complex suggests that receptor dimerization is not sufficient for activation. NATURE STRUCTURAL BIOLOGY 1998; 5:993-1004. [PMID: 9808045 DOI: 10.1038/2965] [Citation(s) in RCA: 163] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dimerization of the erythropoietin (EPO) receptor (EPOR), in the presence of either natural (EPO) or synthetic (EPO-mimetic peptides, EMPs) ligands is the principal extracellular event that leads to receptor activation. The crystal structure of the extracellular domain of EPOR bound to an inactive (antagonist) peptide at 2.7 A resolution has unexpectedly revealed that dimerization still occurs, but the orientation between receptor molecules is altered relative to active (agonist) peptide complexes. Comparison of the biological properties of agonist and antagonist EMPs with EPO suggests that the extracellular domain orientation is tightly coupled to the cytoplasmic signaling events and, hence, provides valuable new insights into the design of synthetic ligands for EPOR and other cytokine receptors.
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Affiliation(s)
- O Livnah
- Department of Molecular Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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19
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Syed RS, Reid SW, Li C, Cheetham JC, Aoki KH, Liu B, Zhan H, Osslund TD, Chirino AJ, Zhang J, Finer-Moore J, Elliott S, Sitney K, Katz BA, Matthews DJ, Wendoloski JJ, Egrie J, Stroud RM. Efficiency of signalling through cytokine receptors depends critically on receptor orientation. Nature 1998; 395:511-6. [PMID: 9774108 DOI: 10.1038/26773] [Citation(s) in RCA: 418] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Human erythropoietin is a haematopoietic cytokine required for the differentiation and proliferation of precursor cells into red blood cells. It activates cells by binding and orientating two cell-surface erythropoietin receptors (EPORs) which trigger an intracellular phosphorylation cascade. The half-maximal response in a cellular proliferation assay is evoked at an erythropoietin concentration of 10 pM, 10(-2) of its Kd value for erythropoietin-EPOR binding site 1 (Kd approximately equal to nM), and 10(-5) of the Kd for erythropoietin-EPOR binding site 2 (Kd approximately equal to 1 microM). Overall half-maximal binding (IC50) of cell-surface receptors is produced with approximately 0.18 nM erythropoietin, indicating that only approximately 6% of the receptors would be bound in the presence of 10 pM erythropoietin. Other effective erythropoietin-mimetic ligands that dimerize receptors can evoke the same cellular responses but much less efficiently, requiring concentrations close to their Kd values (approximately 0.1 microM). The crystal structure of erythropoietin complexed to the extracellular ligand-binding domains of the erythropoietin receptor, determined at 1.9 A from two crystal forms, shows that erythropoietin imposes a unique 120 degrees angular relationship and orientation that is responsible for optimal signalling through intracellular kinase pathways.
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Affiliation(s)
- R S Syed
- Amgen Inc., Thousand Oaks, California 91320-1789, USA.
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20
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Barth HG, Boyes BE, Jackson C. Size Exclusion Chromatography and Related Separation Techniques. Anal Chem 1998. [DOI: 10.1021/a1980015t] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Howard G. Barth
- Central Research and Development, DuPont Company, Experimental Station, P.O. Box 80228, Wilmington, Delaware 19880-0228, Little Falls Analytical DivisionNewport, Hewlett-Packard Company, 538 First State Boulevard, Newport, Delaware 19804, and Marshall Laboratory, DuPont Automative Products, 3401 Grays Ferry Avenue, Philadelphia, Pennsylvania 19146
| | - Barry E. Boyes
- Central Research and Development, DuPont Company, Experimental Station, P.O. Box 80228, Wilmington, Delaware 19880-0228, Little Falls Analytical DivisionNewport, Hewlett-Packard Company, 538 First State Boulevard, Newport, Delaware 19804, and Marshall Laboratory, DuPont Automative Products, 3401 Grays Ferry Avenue, Philadelphia, Pennsylvania 19146
| | - Christian Jackson
- Central Research and Development, DuPont Company, Experimental Station, P.O. Box 80228, Wilmington, Delaware 19880-0228, Little Falls Analytical DivisionNewport, Hewlett-Packard Company, 538 First State Boulevard, Newport, Delaware 19804, and Marshall Laboratory, DuPont Automative Products, 3401 Grays Ferry Avenue, Philadelphia, Pennsylvania 19146
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21
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Johnson DL, Farrell FX, Barbone FP, McMahon FJ, Tullai J, Kroon D, Freedy J, Zivin RA, Mulcahy LS, Jolliffe LK. Amino-terminal dimerization of an erythropoietin mimetic peptide results in increased erythropoietic activity. CHEMISTRY & BIOLOGY 1997; 4:939-50. [PMID: 9427659 DOI: 10.1016/s1074-5521(97)90302-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Erythropoietin (EPO), the hormone involved in red blood cell production, activates its receptor by binding to the receptor's extracellular domain and presumably dimerizing two receptor monomers to initiate signal transduction. EPO-mimetic peptides, such as EMP1, also bind and activate the receptor by dimerization. These mimetic peptides are not as potent as EPO, however. The crystal structure of the EPO receptor (EBP) bound to EMP1 reveals the formation of a complex consisting of two peptides bound to two receptors, so we sought to improve the biological activity of EPO-mimetic peptides by constructing covalent dimers of EMP1 and other peptide mimetics linked by polyethylene glycol (PEG). RESULTS The potency of the PEG-dimerized EPO peptide mimetics both in vitro and in vivo was improved up to 1,000-fold compared to the corresponding peptide monomers. The dimers were constructed using peptide monomers which have only one reactive amine per molecule, allowing us to conclude that the increase in potency can be attributed to a structure in which two peptides are linked through their respective amino termini to the difunctional PEG molecule. In addition, an inactive peptide was converted into a weak agonist by PEG-induced dimerization. CONCLUSIONS The potency of previously isolated peptides that are modest agonists of the EPO receptor was dramatically increased by PEG-induced dimerization. The EPO receptor is thought to be dimerized during activation, so our results are consistent with the proposed 2:2 receptor : peptide stoichiometry. The conversion of an inactive peptide into an agonist further supports the idea that dimerization can mediate receptor activation.
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Affiliation(s)
- D L Johnson
- Drug Discovery Research, R.W. Johnson Pharmaceutical Research Institute, Route 202, Box 300, Raritan, NJ 08869, USA. . com
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22
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Haniu M, Montestruque S, Bures EJ, Talvenheimo J, Toso R, Lewis-Sandy S, Welcher AA, Rohde MF. Interactions between brain-derived neurotrophic factor and the TRKB receptor. Identification of two ligand binding domains in soluble TRKB by affinity separation and chemical cross-linking. J Biol Chem 1997; 272:25296-303. [PMID: 9312147 DOI: 10.1074/jbc.272.40.25296] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The extracellular domain of the human neurotrophin TRKB receptor expressed in Chinese hamster ovary cells is a highly glycosylated protein, possessing binding ability for brain-derived neurotrophic factor (BDNF). Two distinct ligand binding domains of TRKB were isolated from proteolytic digests of the receptor by affinity separation on immobilized BDNF. One of these domains consists of amino acid residues 103-181 and contains both the third leucine-rich motif and the second cysteine cluster domain. The second domain is close to the second immunoglobulin-like domain (amino acid residues 342-394). Each of these two domains can bind BDNF independently. Disulfide linkages present in the first domain are necessary for BDNF binding, probably because of preservation of the native conformation. To study the second domain in greater detail, a truncated form of TRKB containing the second immunoglobulin-like domain (residues 248-398) was expressed in Escherichia coli. This domain was cross-linked to BDNF through a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide coupling reaction. Several synthetic peptides corresponding to amino acid residues 343-379 were able to bind immobilized BDNF. Amino acid substitution and cross-linking analysis indicated that amino acids Phe347, Asp354, and Tyr361 are intimately involved in BDNF binding. These results, obtained from a variety of experimental techniques, highlight the importance of two distinct regions of the extracellular domain of the TRKB receptor in binding BDNF.
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Affiliation(s)
- M Haniu
- Departments of Protein Structure, Protein Chemistry, and Immunology, Amgen, Inc., Thousand Oaks, California 91320, USA. mhaniu@amgen
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23
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Barbone FP, Middleton SA, Johnson DL, McMahon FJ, Tullai J, Gruninger RH, Schilling AE, Jolliffe LK, Mulcahy LS. Mutagenesis studies of the human erythropoietin receptor. Establishment of structure-function relationships. J Biol Chem 1997; 272:4985-92. [PMID: 9030560 DOI: 10.1074/jbc.272.8.4985] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Mutagenesis of the erythropoietin receptor (EPOR) permits analysis of the contribution that individual amino acid residues make to erythropoietin (EPO) binding. We employed both random and site-specific mutagenesis to determine the function of amino acid residues in the extracellular domain (referred to as EPO binding protein, EBP) of the EPOR. Residues were chosen for site-specific alanine substitution based on the results of the random mutagenesis or on their homology to residues that are conserved or have been reported to be involved in ligand binding in other receptors of the cytokine receptor family. Site-specific mutants were expressed in Escherichia coli as soluble EBP and analyzed for EPO binding in several different assay formats. In addition, selected mutant proteins were expressed as full-length EPOR on the surface of COS cells and analyzed for 125I-EPO binding in receptor binding assays. Using these methods, we have identified residues that appear to be involved in EPO binding as well as other residues, most of which are conserved in receptors of the cytokine receptor family, that appear to be necessary for the proper folding and/or stability of the EPOR. We present correlations between these mutagenesis data and the recently solved crystal structure of the EBP with a peptide ligand.
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Affiliation(s)
- F P Barbone
- The R. W. Johnson Pharmaceutical Research Institute, Drug Discovery Research, Raritan, New Jersey 08869, USA.
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24
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Abstract
Progress in our understanding of several biological processes promises to broaden the usefulness of Escherichia coli as a tool for gene expression. There is an expanding choice of tightly regulated prokaryotic promoters suitable for achieving high-level gene expression. New host strains facilitate the formation of disulfide bonds in the reducing environment of the cytoplasm and offer higher protein yields by minimizing proteolytic degradation. Insights into the process of protein translocation across the bacterial membranes may eventually make it possible to achieve robust secretion of specific proteins into the culture medium. Studies involving molecular chaperones have shown that in specific cases, chaperones can be very effective for improved protein folding, solubility, and membrane transport. Negative results derived from such studies are also instructive in formulating different strategies. The remarkable increase in the availability of fusion partners offers a wide range of tools for improved protein folding, solubility, protection from proteases, yield, and secretion into the culture medium, as well as for detection and purification of recombinant proteins. Codon usage is known to present a potential impediment to high-level gene expression in E. coli. Although we still do not understand all the rules governing this phenomenon, it is apparent that "rare" codons, depending on their frequency and context, can have an adverse effect on protein levels. Usually, this problem can be alleviated by modification of the relevant codons or by coexpression of the cognate tRNA genes. Finally, the elucidation of specific determinants of protein degradation, a plethora of protease-deficient host strains, and methods to stabilize proteins afford new strategies to minimize proteolytic susceptibility of recombinant proteins in E. coli.
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Affiliation(s)
- S C Makrides
- Department of Molecular Biology, T Cell Sciences, Inc., Needham, Massachusetts 02194, USA
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25
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Wrighton NC, Farrell FX, Chang R, Kashyap AK, Barbone FP, Mulcahy LS, Johnson DL, Barrett RW, Jolliffe LK, Dower WJ. Small peptides as potent mimetics of the protein hormone erythropoietin. Science 1996; 273:458-64. [PMID: 8662529 DOI: 10.1126/science.273.5274.458] [Citation(s) in RCA: 506] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Random phage display peptide libraries and affinity selective methods were used to isolate small peptides that bind to and activate the receptor for the cytokine erythropoietin (EPO). In a panel of in vitro biological assays, the peptides act as full agonists and they can also stimulate erythropoiesis in mice. These agonists are represented by a 14- amino acid disulfide-bonded, cyclic peptide with the minimum consensus sequence YXCXXGPXTWXCXP, where X represents positions allowing occupation by several amino acids. The amino acid sequences of these peptides are not found in the primary sequence of EPO. The signaling pathways activated by these peptides appear to be identical to those induced by the natural ligand. This discovery may form the basis for the design of small molecule mimetics of EPO.
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Affiliation(s)
- N C Wrighton
- Affymax Research Institute, 4001 Miranda Avenue, Palo Alto, CA 94304, USA
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26
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Livnah O, Stura EA, Johnson DL, Middleton SA, Mulcahy LS, Wrighton NC, Dower WJ, Jolliffe LK, Wilson IA. Functional mimicry of a protein hormone by a peptide agonist: the EPO receptor complex at 2.8 A. Science 1996; 273:464-71. [PMID: 8662530 DOI: 10.1126/science.273.5274.464] [Citation(s) in RCA: 501] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The functional mimicry of a protein by an unrelated small molecule has been a formidable challenge. Now, however, the biological activity of a 166-residue hematopoietic growth hormone, erythropoietin (EPO), with its class 1 cytokine receptor has been mimicked by a 20-residue cyclic peptide unrelated in sequence to the natural ligand. The crystal structure at 2.8 A resolution of a complex of this agonist peptide with the extracellular domain of EPO receptor reveals that a peptide dimer induces an almost perfect twofold dimerization of the receptor. The dimer assembly differs from that of the human growth hormone (hGH) receptor complex and suggests that more than one mode of dimerization may be able to induce signal transduction and cell proliferation. The EPO receptor binding site, defined by peptide interaction, corresponds to the smaller functional epitope identified for hGH receptor. Similarly, the EPO mimetic peptide ligand can be considered as a minimal hormone, and suggests the design of nonpeptidic small molecule mimetics for EPO and other cytokines may indeed be achievable.
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MESH Headings
- Amino Acid Sequence
- Binding Sites
- Crystallography, X-Ray
- Drug Design
- Erythropoietin/chemistry
- Erythropoietin/metabolism
- Growth Hormone/chemistry
- Growth Hormone/metabolism
- Humans
- Hydrogen Bonding
- Models, Molecular
- Molecular Mimicry
- Molecular Sequence Data
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/metabolism
- Protein Conformation
- Protein Folding
- Protein Structure, Secondary
- Receptors, Erythropoietin/agonists
- Receptors, Erythropoietin/chemistry
- Receptors, Erythropoietin/metabolism
- Receptors, Somatotropin/chemistry
- Receptors, Somatotropin/metabolism
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Affiliation(s)
- O Livnah
- Department of Molecular Biology and the Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10666 North Torrey Pines Road, La Jolla, CA 92037, USA
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27
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Middleton SA, Johnson DL, Jin R, McMahon FJ, Collins A, Tullai J, Gruninger RH, Jolliffe LK, Mulcahy LS. Identification of a critical ligand binding determinant of the human erythropoietin receptor. Evidence for common ligand binding motifs in the cytokine receptor family. J Biol Chem 1996; 271:14045-54. [PMID: 8662939 DOI: 10.1074/jbc.271.24.14045] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The erythropoietin receptor (EPOR) is a member of a family of cytokine and growth factor receptors that share conserved features in their extracellular and cytoplasmic domains. We have used site-specific mutagenesis within the extracellular domain of the EPOR to search for amino acid residues involved in erythropoietin (EPO) binding. Mutant proteins were expressed in bacteria as soluble EPO binding proteins (EBP) and characterized for EPO binding activity in a number of different assays. Substitution of phenylalanine at position 93 (Phe93) with alanine (F93A mutation) resulted in a drastic reduction in EPO binding in the EBP. More conservative tyrosine or tryptophan substitutions at Phe93 resulted in much less dramatic effects on EPO binding. Biophysical studies indicated that the F93A mutation does not result in gross structural alterations in the EBP. Furthermore, the F93A mutation in full-length EPOR expressed in COS cells abolished detectable EPO binding. This was not a result of processing or transport defects, since mutant receptor was present on the surface of the cells. Mutations in the region immediately around Phe93 and in residues homologous to other reported ligand binding determinants of the cytokine receptor family had small to moderate effects on EPO binding. These data indicate that Phe93 is a critical EPO binding determinant of the EPOR. Furthermore, since Phe93 aligns with critical ligand binding determinants in other receptors of the cytokine receptor family, these data suggest that receptors of this family may use common structural motifs to bind their cognate ligands.
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Affiliation(s)
- S A Middleton
- R. W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey 08869, USA
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