1
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Sachdev S, Creemer BA, Gardella TJ, Cheloha RW. Highly biased agonism for GPCR ligands via nanobody tethering. Nat Commun 2024; 15:4687. [PMID: 38824166 PMCID: PMC11144202 DOI: 10.1038/s41467-024-49068-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 05/22/2024] [Indexed: 06/03/2024] Open
Abstract
Ligand-induced activation of G protein-coupled receptors (GPCRs) can initiate signaling through multiple distinct pathways with differing biological and physiological outcomes. There is intense interest in understanding how variation in GPCR ligand structure can be used to promote pathway selective signaling ("biased agonism") with the goal of promoting desirable responses and avoiding deleterious side effects. Here we present an approach in which a conventional peptide ligand for the type 1 parathyroid hormone receptor (PTHR1) is converted from an agonist which induces signaling through all relevant pathways to a compound that is highly selective for a single pathway. This is achieved not through variation in the core structure of the agonist, but rather by linking it to a nanobody tethering agent that binds with high affinity to a separate site on the receptor not involved in signal transduction. The resulting conjugate represents the most biased agonist of PTHR1 reported to date. This approach holds promise for facile generation of pathway selective ligands for other GPCRs.
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Affiliation(s)
- Shivani Sachdev
- Laboratory of Bioorganic Chemistry, National Institutes of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bathesda, MD, USA
| | - Brendan A Creemer
- Laboratory of Bioorganic Chemistry, National Institutes of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bathesda, MD, USA
| | - Thomas J Gardella
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Ross W Cheloha
- Laboratory of Bioorganic Chemistry, National Institutes of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bathesda, MD, USA.
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2
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Liu S, Daley EJ, My-Linh Tran L, Yu Z, Reyes M, Dean T, Khatri A, Levine PM, Balana AT, Pratt MR, Jüppner H, Gellman SH, Gardella TJ. Backbone Modification Provides a Long-Acting Inverse Agonist of Pathogenic, Constitutively Active PTH1R Variants. J Am Chem Soc 2024; 146:6522-6529. [PMID: 38417010 PMCID: PMC11162201 DOI: 10.1021/jacs.3c09694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2024]
Abstract
Parathyroid hormone 1 receptor (PTH1R) plays a key role in mediating calcium homeostasis and bone development, and aberrant PTH1R activity underlies several human diseases. Peptidic PTH1R antagonists and inverse agonists have therapeutic potential in treating these diseases, but their poor pharmacokinetics and pharmacodynamics undermine their in vivo efficacy. Herein, we report the use of a backbone-modification strategy to design a peptidic PTH1R inhibitor that displays prolonged activity as an antagonist of wild-type PTH1R and an inverse agonist of the constitutively active PTH1R-H223R mutant both in vitro and in vivo. This peptide may be of interest for the future development of therapeutic agents that ameliorate PTH1R malfunction.
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Affiliation(s)
- Shi Liu
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Eileen J Daley
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Lauren My-Linh Tran
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Zhen Yu
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Monica Reyes
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Thomas Dean
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Ashok Khatri
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Paul M Levine
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Aaron T Balana
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Matthew R Pratt
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Harald Jüppner
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Samuel H. Gellman
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Thomas J Gardella
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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3
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Peña KA, Savransky S, Lewis B. Endosomal signaling via cAMP in parathyroid hormone (PTH) type 1 receptor biology. Mol Cell Endocrinol 2024; 581:112107. [PMID: 37981188 DOI: 10.1016/j.mce.2023.112107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 10/25/2023] [Accepted: 11/06/2023] [Indexed: 11/21/2023]
Abstract
Compartmentalization of GPCR signaling is an emerging topic that highlights the physiological relevance of spatial bias in signaling. The parathyroid hormone (PTH) type 1 receptor (PTH1R) was the first GPCR described to signal via heterotrimeric G-protein and cAMP from endosomes after β-arrestin mediated internalization, challenging the canonical GPCR signaling model which established that signaling is terminated by receptor internalization. More than a decade later, many other GPCRs have been shown to signal from endosomes via cAMP, and recent studies have proposed that location of cAMP generation impacts physiological outcomes of GPCR signaling. Here, we review the extensive literature regarding PTH1R endosomal signaling via cAMP, the mechanisms that regulate endosomal generation of cAMP, and the implications of spatial bias in PTH1R physiological functions.
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Affiliation(s)
- Karina A Peña
- Laboratory for GPCR Biology, Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
| | - Sofya Savransky
- Laboratory for GPCR Biology, Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; Graduate Program in Molecular Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Breanna Lewis
- Laboratory for GPCR Biology, Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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4
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Sachdev S, Creemer BA, Gardella TJ, Cheloha RW. Highly biased agonism for GPCR ligands via nanobody tethering. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.10.561766. [PMID: 37873435 PMCID: PMC10592785 DOI: 10.1101/2023.10.10.561766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Ligand-induced activation of G protein-coupled receptors (GPCRs) can initiate signaling through multiple distinct pathways with differing biological and physiological outcomes. There is intense interest in understanding how variation in GPCR ligand structure can be used to promote pathway selective signaling ("biased agonism") with the goal of promoting desirable responses and avoiding deleterious side effects. Here we present a new approach in which a conventional peptide ligand for the type 1 parathyroid hormone receptor (PTHR1) is converted from an agonist which induces signaling through all relevant pathways to a compound that is highly selective for a single pathway. This is achieved not through variation in the core structure of the agonist, but rather by linking it to a nanobody tethering agent that binds with high affinity to a separate site on the receptor not involved in signal transduction. The resulting conjugate represents the most biased agonist of PTHR1 reported to date. This approach holds promise for facile generation of pathway selective ligands for other GPCRs.
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5
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Gibadullin R, Kim TW, Tran LML, Gellman SH. Hormone Analogues with Unique Signaling Profiles from Replacement of α-Residue Triads with β/γ Diads. J Am Chem Soc 2023; 145:20539-20550. [PMID: 37697685 PMCID: PMC10588032 DOI: 10.1021/jacs.3c06703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/13/2023]
Abstract
We have applied an underexplored backbone modification strategy to generate new analogues of peptides that activate two clinically important class B1 G protein-coupled receptors (GPCRs). Most peptide modification strategies involve changing side chains or, less commonly, changing the configuration at side chain-bearing carbons (i.e., l residues replaced by d residues). In contrast, backbone modifications alter the number of backbone atoms and the identities of backbone atoms relative to a poly-α-amino acid backbone. Starting from the peptide agonists PTH(1-34) (the first 34 residues of the parathyroid hormone, used clinically as the drug teriparatide) and glucagon-like peptide-1 (7-36) (GLP-1(7-36)), we replaced native α-residue triads with a diad composed of a β-amino acid residue and a γ-amino acid residue. The β/γ diad retains the number of backbone atoms in the ααα triad. Because the β and γ residue each bear a single side chain, we implemented ααα→βγ replacements at sites that contained a Gly residue (i.e., at α-residue triads that presented only two side chains). All seven of the α/β/γ-peptides derived from PTH(1-34) or GLP-1(7-36) bind to the cognate receptor (the PTHR1 or the GLP-1R), but they vary considerably in their activity profiles. Outcomes include functional mimicry of the all-α agonist, receptor-selective agonist activity, biased agonism, or strong binding with weak activation, which could lead to antagonist development. Collectively, these findings demonstrate that ααα→βγ replacements, which are easily implemented via solid-phase synthesis, can generate peptide hormone analogues that display unique and potentially useful signaling behavior.
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Affiliation(s)
- Ruslan Gibadullin
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
- Present address: Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Tae Wook Kim
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Lauren My-Linh Tran
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Samuel H. Gellman
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
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6
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Guo Z, Huang T, Liu Y, Liu C. Parathyroid Hormone-Related Protein Promotes the Proliferation of Patient-Derived Glioblastoma Stem Cells via Activating cAMP/PKA Signaling Pathway. Int J Stem Cells 2023; 16:315-325. [PMID: 37385633 PMCID: PMC10465338 DOI: 10.15283/ijsc22097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Revised: 09/14/2022] [Accepted: 11/01/2022] [Indexed: 07/01/2023] Open
Abstract
Background and Objectives Glioblastoma (GBM) is an aggressive primary brain tumor characterized by its heterogeneity and high recurrence and lethality rates. Glioblastoma stem cells (GSCs) play a crucial role in therapy resistance and tumor recurrence. Therefore, targeting GSCs is a key objective in developing effective treatments for GBM. The role of Parathyroid hormone-related peptide (PTHrP) in GBM and its impact on GSCs remains unclear. This study aimed to investigate the effect of PTHrP on GSCs and its potential as a therapeutic target for GBM. Methods and Results Using the Cancer Genome Atlas (TCGA) database, we found higher expression of PTHrP in GBM, which correlated inversely with survival. GSCs were established from three human GBM samples obtained after surgical resection. Exposure to recombinant human PTHrP protein (rPTHrP) at different concentrations significantly enhanced GSCs viability. Knockdown of PTHrP using target-specific siRNA (siPTHrP) inhibited tumorsphere formation and reduced the number of BrdU-positive cells. In an orthotopic xenograft mouse model, suppression of PTHrP expression led to significant inhibition of tumor growth. The addition of rPTHrP in the growth medium counteracted the antiproliferative effect of siPTHrP. Further investigation revealed that PTHrP increased cAMP concentration and activated the PKA signaling pathway. Treatment with forskolin, an adenylyl cyclase activator, nullified the antiproliferative effect of siPTHrP. Conclusions Our findings demonstrate that PTHrP promotes the proliferation of patient-derived GSCs by activating the cAMP/PKA signaling pathway. These results uncover a novel role for PTHrP and suggest its potential as a therapeutic target for GBM treatment.
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Affiliation(s)
- Zhenyu Guo
- Department of Neurosurgery, The 2nd Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Tingqin Huang
- Department of Neurosurgery, The 2nd Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
| | - Yingfei Liu
- Institute of Neurobiology, Xi’an Jiaotong University Health Science Center, Xi’an, China
| | - Chongxiao Liu
- Department of Neurosurgery, The 2nd Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
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7
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Portales-Castillo I, Dean T, Cheloha RW, Creemer BA, Vilardaga JP, Savransky S, Khatri A, Jüppner H, Gardella TJ. Altered Signaling and Desensitization Responses in PTH1R Mutants Associated with Eiken Syndrome. Commun Biol 2023; 6:599. [PMID: 37268817 PMCID: PMC10238420 DOI: 10.1038/s42003-023-04966-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 05/22/2023] [Indexed: 06/04/2023] Open
Abstract
The parathyroid hormone receptor type 1 (PTH1R) is a G protein-coupled receptor that plays key roles in regulating calcium homeostasis and skeletal development via binding the ligands, PTH and PTH-related protein (PTHrP), respectively. Eiken syndrome is a rare disease of delayed bone mineralization caused by homozygous PTH1R mutations. Of the three mutations identified so far, R485X, truncates the PTH1R C-terminal tail, while E35K and Y134S alter residues in the receptor's amino-terminal extracellular domain. Here, using a variety of cell-based assays, we show that R485X increases the receptor's basal rate of cAMP signaling and decreases its capacity to recruit β-arrestin2 upon ligand stimulation. The E35K and Y134S mutations each weaken the binding of PTHrP leading to impaired β-arrestin2 recruitment and desensitization of cAMP signaling response to PTHrP but not PTH. Our findings support a critical role for interaction with β-arrestin in the mechanism by which the PTH1R regulates bone formation.
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Affiliation(s)
- Ignacio Portales-Castillo
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
- Department of Medicine, Division of Nephrology, Massachusetts General Hospital, and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
- Department of Medicine, Division of Nephrology, Washington University in St. Louis, BJCIH Building, 425 South Euclid St, St. Louis, MO, 63110, USA
| | - Thomas Dean
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
| | - Ross W Cheloha
- Chemical Biology in Signaling Section, Laboratory of Bioorganic Chemistry, National Institutes of Diabetes and Digestive and Kidney Diseases, Building 8, 8 Center Drive, Bethesda, MD, 20891, USA
| | - Brendan A Creemer
- Chemical Biology in Signaling Section, Laboratory of Bioorganic Chemistry, National Institutes of Diabetes and Digestive and Kidney Diseases, Building 8, 8 Center Drive, Bethesda, MD, 20891, USA
| | - Jean-Pierre Vilardaga
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Thomas E. Starzl Biomedical Science Tower, 200 Lothrop St, Pittsburgh, PA, 15261, USA
| | - Sofya Savransky
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Thomas E. Starzl Biomedical Science Tower, 200 Lothrop St, Pittsburgh, PA, 15261, USA
| | - Ashok Khatri
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
| | - Harald Jüppner
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
- Pediatric Nephrology Unit, Massachusetts General Hospital, and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA
| | - Thomas J Gardella
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Thier Research Building, 50 Blossom St, Boston, MA, 02114, USA.
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8
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Cary BP, Zhang X, Cao J, Johnson RM, Piper SJ, Gerrard EJ, Wootten D, Sexton PM. New insights into the structure and function of class B1 GPCRs. Endocr Rev 2022; 44:492-517. [PMID: 36546772 PMCID: PMC10166269 DOI: 10.1210/endrev/bnac033] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 11/07/2022] [Accepted: 12/14/2022] [Indexed: 12/24/2022]
Abstract
G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors. Class B1 GPCRs constitute a subfamily of 15 receptors that characteristically contain large extracellular domains (ECDs) and respond to long polypeptide hormones. Class B1 GPCRs are critical regulators of homeostasis, and as such, many are important drug targets. While most transmembrane proteins, including GPCRs, are recalcitrant to crystallization, recent advances in electron cryo-microscopy (cryo-EM) have facilitated a rapid expansion of the structural understanding of membrane proteins. As a testament to this success, structures for all the class B1 receptors bound to G proteins have been determined by cryo-EM in the past five years. Further advances in cryo-EM have uncovered dynamics of these receptors, ligands, and signalling partners. Here, we examine the recent structural underpinnings of the class B1 GPCRs with an emphasis on structure-function relationships.
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Affiliation(s)
- Brian P Cary
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Xin Zhang
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Jianjun Cao
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Rachel M Johnson
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Sarah J Piper
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Elliot J Gerrard
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Denise Wootten
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Patrick M Sexton
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.,ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
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9
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Altered signaling at the PTH receptor via modified agonist contacts with the extracellular domain provides a path to prolonged agonism in vivo. Proc Natl Acad Sci U S A 2022; 119:e2212736119. [PMID: 36409914 PMCID: PMC9860328 DOI: 10.1073/pnas.2212736119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The parathyroid hormone type 1 receptor (PTHR1), a Class B GPCR, is activated by long polypeptides, including drugs for osteoporosis and hypoparathyroidism. The PTHR1 engages peptide agonists via a two-step mechanism. Initial contact involves the extracellular domain (ECD), which has been thought to contribute primarily to receptor-peptide binding, and then the N terminus of the peptide engages the receptor transmembrane domain (TMD), which is thought to control the message conveyed to intracellular partners. This mechanism has been suggested to apply to other Class B GPCRs as well. Here, we show that modification of a PTHR1 agonist at ECD-contact sites can alter the signaling profile, an outcome that is not accommodated by the current two-step binding model. Our data support a modified two-step binding model in which agonist orientation on the ECD surface can influence the geometry of agonist-TMD engagement. This expanded binding model offers a mechanism by which altering ECD-contact residues can affect signaling profile. Our discoveries provide a rationale for exploring agonist modifications distal from the TMD-contact region in future efforts to optimize therapeutic performance of peptide hormone analogs.
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10
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Peña KA. Endosomal parathyroid hormone receptor signaling. Am J Physiol Cell Physiol 2022; 323:C783-C790. [PMID: 35912987 PMCID: PMC9467467 DOI: 10.1152/ajpcell.00452.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 07/20/2022] [Accepted: 07/25/2022] [Indexed: 11/22/2022]
Abstract
The canonical model for G protein-coupled receptors (GPCRs) activation assumes that stimulation of heterotrimeric G protein signaling upon ligand binding occurs solely at the cell surface and that duration of the stimulation is transient to prevent overstimulation. In this model, GPCR signaling is turned-off by receptor phosphorylation via GPCR kinases (GRKs) and subsequent recruitment of β-arrestins, resulting in receptor internalization into endosomes. Internalized receptors can then recycle back to the cell surface or be trafficked to lysosomes for degradation. However, over the last decade, this model has been extended by discovering that some internalized GPCRs continue to signal via G proteins from endosomes. This is the case for the parathyroid hormone (PTH) type 1 receptor (PTHR), which engages on sustained cAMP signaling from endosomes upon PTH stimulation. Accumulative evidence shows that the location of signaling has an impact on the physiological effects of GPCR signaling. This mini-review discusses recent insights into the mechanisms of PTHR endosomal signaling and its physiological impact.
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Affiliation(s)
- Karina A Peña
- Laboratory for GPCR Biology, Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
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11
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Peña KA, White AD, Savransky S, Castillo IP, Jean-Alphonse FG, Gardella TJ, Sutkeviciute I, Vilardaga JP. Biased GPCR signaling by the native parathyroid hormone-related protein 1-141 relative to its N-terminal fragment 1-36. J Biol Chem 2022; 298:102332. [PMID: 35933010 PMCID: PMC9437850 DOI: 10.1016/j.jbc.2022.102332] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 11/13/2022] Open
Abstract
The parathyroid hormone (PTH)–related protein (PTHrP) is indispensable for the development of mammary glands, placental calcium ion transport, tooth eruption, bone formation and bone remodeling, and causes hypercalcemia in patients with malignancy. Although mature forms of PTHrP in the body consist of splice variants of 139, 141, and 173 amino acids, our current understanding on how endogenous PTHrP transduces signals through its cognate G-protein coupled receptor (GPCR), the PTH type 1 receptor (PTHR), is largely derived from studies done with its N-terminal fragment, PTHrP1-36. Here, we demonstrate using various fluorescence imaging approaches at the single cell level to measure kinetics of (i) receptor activation, (ii) receptor signaling via Gs and Gq, and (iii) receptor internalization and recycling that the native PTHrP1-141 displays biased agonist signaling properties that are not mimicked by PTHrP1-36. Although PTHrP1–36 induces transient cAMP production, acute intracellular Ca2+ (iCa2+) release and β-arrestin recruitment mediated by ligand–PTHR interactions at the plasma membrane, PTHrP1-141 triggers sustained cAMP signaling from the plasma membrane and fails to stimulate iCa2+ release and recruit β-arrestin. Furthermore, we show that the molecular basis for biased signaling differences between PTHrP1-36 and properties of native PTHrP1-141 are caused by the stabilization of a singular PTHR conformation and PTHrP1-141 sensitivity to heparin, a sulfated glycosaminoglycan. Taken together, our results contribute to a better understanding of the biased signaling process of a native protein hormone acting in conjunction with a GPCR.
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Affiliation(s)
- Karina A Peña
- Department of Pharmacology and Chemical Biology, Pittsburgh PA 15261, USA
| | - Alex D White
- Department of Pharmacology and Chemical Biology, Pittsburgh PA 15261, USA
| | - Sofya Savransky
- Department of Pharmacology and Chemical Biology, Pittsburgh PA 15261, USA; Graduate Program in Molecular Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh PA 15261, USA
| | | | | | - Thomas J Gardella
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Ieva Sutkeviciute
- Department of Pharmacology and Chemical Biology, Pittsburgh PA 15261, USA
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12
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Yoon SH, Tang CC, Wein MN. Salt inducible kinases and PTH1R action. VITAMINS AND HORMONES 2022; 120:23-45. [PMID: 35953111 DOI: 10.1016/bs.vh.2022.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Parathyroid hormone is a central regulator of calcium homeostasis. PTH protects the organism from hypocalcemia through its actions in bone and kidney. Recent physiologic studies have revealed key target genes for PTH receptor (PTH1R) signaling in these target organs. However, the complete signal transduction cascade used by PTH1R to accomplish these physiologic actions has remained poorly defined. Here we will review recent studies that have defined an important role for salt inducible kinases downstream of PTH1R in bone, cartilage, and kidney. PTH1R signaling inhibits the activity of salt inducible kinases. Therefore, direct SIK inhibitors represent a promising novel strategy to mimic PTH actions using small molecules. Moreover, a detailed understanding of the molecular circuitry used by PTH1R to exert its biologic effects will afford powerful new models to better understand the diverse actions of this important G protein coupled receptor in health and disease.
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Affiliation(s)
- Sung-Hee Yoon
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
| | - Cheng-Chia Tang
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
| | - Marc N Wein
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States.
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13
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Daley EJ, Yoon SH, Reyes M, Bruce M, Brooks DJ, Bouxsein M, Potts JT, Kronenberg HM, Wein MN, Lanske B, Jüppner H, Gardella TJ. Actions of Parathyroid Hormone Ligand Analogues in Humanized PTH1R Knockin Mice. Endocrinology 2022; 163:6573221. [PMID: 35460406 PMCID: PMC9167040 DOI: 10.1210/endocr/bqac054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Indexed: 11/19/2022]
Abstract
Rodent models are commonly used to evaluate parathyroid hormone (PTH) and PTH-related protein (PTHrP) ligands and analogues for their pharmacologic activities and potential therapeutic utility toward diseases of bone and mineral ion metabolism. Divergence, however, in the amino acid sequences of rodent and human PTH receptors (rat and mouse PTH1Rs are 91% identical to the human PTH1R) can lead to differences in receptor-binding and signaling potencies for such ligands when assessed on rodent vs human PTH1Rs, as shown by cell-based assays in vitro. This introduces an element of uncertainty in the accuracy of rodent models for performing such preclinical evaluations. To overcome this potential uncertainty, we used a homologous recombination-based knockin (KI) approach to generate a mouse (in-host strain C57Bl/6N) in which complementary DNA encoding the human PTH1R replaces a segment (exon 4) of the murine PTH1R gene so that the human and not the mouse PTH1R protein is expressed. Expression is directed by the endogenous mouse promoter and hence occurs in all biologically relevant cells and tissues and at appropriate levels. The resulting homozygous hPTH1R-KI (humanized) mice were healthy over at least 10 generations and showed functional responses to injected PTH analog peptides that are consistent with a fully functional human PTH1R in target bone and kidney cells. The initial evaluation of these mice and their potential utility for predicting behavior of PTH analogues in humans is reported here.
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Affiliation(s)
- Eileen J Daley
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Sung-Hee Yoon
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Monica Reyes
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Michael Bruce
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Daniel J Brooks
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Mary Bouxsein
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - John T Potts
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Henry M Kronenberg
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Marc N Wein
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Beate Lanske
- Radius Health Inc, Boston, Massachusetts 02210, USA
| | - Harald Jüppner
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Thomas J Gardella
- Correspondence: Thomas J. Gardella, PhD, Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Thier 1025, 50 Blossom St, Boston, MA 02114, USA.
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14
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Sang P, Zeng H, Lee C, Shi Y, Wang M, Pan C, Wei L, Huang C, Wu M, Shen W, Li X, Cai J. α/Sulfono-γ-AApeptide Hybrid Analogues of Glucagon with Enhanced Stability and Prolonged In Vivo Activity. J Med Chem 2021; 64:13893-13901. [PMID: 34506138 PMCID: PMC8903076 DOI: 10.1021/acs.jmedchem.1c01289] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Peptide drugs have the advantages of target specificity and good drugability and have become one of the most increasingly important hotspots in new drug research in biomedical sciences. However, peptide drugs generally have low bioavailability and metabolic stability, and therefore, the modification of existing peptide drugs for the purpose of improving stability and retaining activity is of viable importance. It is known that glucagon is an effective therapy for treating severe hypoglycemia, but its short half-life prevents its wide therapeutic use. Herein, we report that combined unnatural residues and long fatty acid conjugation afford potent α/sulfono-γ-AApeptide hybrid analogues of Glucagon with enhanced stability and prolonged in vivo activity. This strategy could be adopted to develop stabilized analogues of other short-acting bioactive peptides.
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Affiliation(s)
- Peng Sang
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Hongxiang Zeng
- Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, China
| | - Candy Lee
- Calibr at Scripps Research, 11119 N. Torrey Pines Rd., La Jolla, California 92037, United States
| | - Yan Shi
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Minghui Wang
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Cong Pan
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Lulu Wei
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Chenglong Huang
- Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, China
| | - Mingjun Wu
- Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, China
| | - Weijun Shen
- Calibr at Scripps Research, 11119 N. Torrey Pines Rd., La Jolla, California 92037, United States
| | - Xi Li
- Institute of Life Sciences, Chongqing Medical University, Chongqing 400016, China
| | - Jianfeng Cai
- Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States
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15
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Abstract
N,N'-linked oligoureas are a class of enantiopure, sequence-defined peptidomimetic oligomers without amino acids that form well-defined and predictable helical structures akin to the peptide α-helix. Oligourea-based foldamers combine a number of features-such as synthetic accessibility, sequence modularity, and folding fidelity-that bode well for their use in a range of applications from medicinal chemistry to catalysis. Moreover, it was recently recognized that this synthetic helical backbone can be combined with regular peptides to generate helically folded peptide-oligourea hybrids that display additional features in terms of helix mimicry and protein-surface recognition properties. Here we provide detailed protocols for the preparation of requested monomers and for the synthesis and purification of homo-oligoureas and peptide-oligourea hybrids.
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16
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Sato T, Verma S, Khatri A, Dean T, Goransson O, Gardella TJ, Wein MN. Comparable Initial Engagement of Intracellular Signaling Pathways by Parathyroid Hormone Receptor Ligands Teriparatide, Abaloparatide, and Long-Acting PTH. JBMR Plus 2021; 5:e10441. [PMID: 33977197 PMCID: PMC8101618 DOI: 10.1002/jbm4.10441] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 11/13/2020] [Accepted: 11/18/2020] [Indexed: 12/21/2022] Open
Abstract
Multiple analogs of parathyroid hormone, all of which bind to the PTH/PTHrP receptor PTH1R, are used for patients with osteoporosis and hypoparathyroidism. Although ligands such as abaloparatide, teriparatide (hPTH 1-34 [TPTD]), and long-acting PTH (LA-PTH) show distinct biologic effects with respect to skeletal and mineral metabolism endpoints, the mechanistic basis for these clinically-important differences remains incompletely understood. Previous work has revealed that differential signaling kinetics and receptor conformation engagement between different PTH1R peptide ligands. However, whether such acute membrane proximal differences translate into differences in downstream signaling output remains to be determined. Here, we directly compared short-term effects of hPTH (1-34), abaloparatide, and LA-PTH in multiple cell-based PTH1R signaling assays. At the time points and ligand concentrations utilized, no significant differences were observed between these three ligands at the level of receptor internalization, β-arrestin recruitment, intracellular calcium stimulation, and cAMP generation. However, abaloparatide showed significantly quicker PTH1R recycling in washout studies. Downstream of PTH1R-stimulated cAMP generation, protein kinase A regulates gene expression via effects on salt inducible kinases (SIKs) and their substrates. Consistent with no differences between these ligands on cAMP generation, we observed that hPTH (1-34), abaloparatide, and LA-PTH showed comparable effects on SIK2 phosphorylation, SIK substrate dephosphorylation, and downstream gene expression changes. Taken together, these results indicate that these PTH1R peptide agonists engage downstream intracellular signaling pathways to a comparable degree. It is possible that differences observed in vivo in preclinical and clinical models may be related to pharmacokinetic factors. It is also possible that our current in vitro systems are insufficient to perfectly match the complexities of PTH1R signaling in bona fide target cells in bone in vivo. © 2020 American Society for Bone and Mineral Research © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.
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Affiliation(s)
- Tadatoshi Sato
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Shiv Verma
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Ashok Khatri
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Thomas Dean
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Olga Goransson
- Department of Experimental Medical ScienceLund University, Diabetes, Metabolism and EndocrinologyLundSweden
| | - Thomas J Gardella
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Marc N Wein
- Endocrine Unit, Department of MedicineMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
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17
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Gibadullin R, Randall CJ, Sidney J, Sette A, Gellman SH. Backbone Modifications of HLA-A2-Restricted Antigens Induce Diverse Binding and T Cell Activation Outcomes. J Am Chem Soc 2021; 143:6470-6481. [PMID: 33881854 DOI: 10.1021/jacs.1c00016] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
CD8+ T cells express T cell receptors (TCRs) that recognize short peptide antigens in the context of major histocompatibility class I (MHC I) molecules. This recognition process produces an array of cytokine-mediated signals that help to govern immunological responses. Design of biostable MHC I peptide vaccines containing unnatural subunits is desirable, and synthetic antigens in which a native α-amino acid residue is replaced by a homologous β-amino acid residue (native side chain but extended backbone) might be useful in this regard. We have evaluated the impact of α-to-β backbone modification at a single site on T cell-mediated recognition of six clinically important viral and tumor-associated antigens bound to an MHC I. Effects of this modification on MHC I affinity and T cell activation were measured. Many of these modifications diminish or prevent T cell response. However, a number of α/β-peptide antigens were found to mimic the activity of natural antigens or to enhance maximal T cell response, as measured by interferon-γ release. Results from this broad exploratory study advance our understanding of immunological responses to antigens bearing unnatural modifications and suggest that α/β-peptides could be a source of potent and proteolytically stable variants of native antigens.
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Affiliation(s)
- Ruslan Gibadullin
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Caleb J Randall
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - John Sidney
- Division of Vaccine Discovery, La Jolla Institute for Immunology, La Jolla, California 92037, United States
| | - Alessandro Sette
- Division of Vaccine Discovery, La Jolla Institute for Immunology, La Jolla, California 92037, United States.,Department of Medicine, University of California, San Diego, California 92093, United States
| | - Samuel H Gellman
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
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18
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Sun C, Li S. PTHR1 in osteosarcoma: Specific molecular mechanisms and comprehensive functional perspective. J Cell Mol Med 2021; 25:3175-3181. [PMID: 33675132 PMCID: PMC8034476 DOI: 10.1111/jcmm.16420] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 02/14/2021] [Accepted: 02/17/2021] [Indexed: 12/14/2022] Open
Abstract
Osteosarcoma occurs largely in children and adolescents and is the most common primary malignant tumour of bone. Although surgical advances and neoadjuvant chemotherapy have made great strides in recent years, rates of local recurrence and lung metastasis remain high, with a plateau in overall survival during the past decade. It is thus urgent to explore the pathogenesis of osteosarcoma and identify potential therapeutic targets. Parathyroid hormone receptor 1 (PTHR1) belongs to the broad family of G protein–coupled receptors, binding both parathyroid hormone (PTH) and parathyroid hormone–related peptide (PTHrP, a paracrine factor). Previous studies have shown that in tissues and cells of osteosarcoma, expression of PTHR1 is markedly increased, correlating with aggressive biologic behaviour and a poor prognosis. PTHR1 expression also correlates closely with epigenetic regulation, transcriptional regulation, post‐translational modification and protein interaction. Herein, we have summarized the latest research on the role played by PTHR1 in progression of osteosarcoma, assessing its clinical utility as a novel biomarker and its therapeutic ramifications.
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Affiliation(s)
- Chaonan Sun
- Department of Radiation Oncology, Cancer Hospital of China Medical University, Liaoning Cancer Hospital & Institute, Shenyang, China
| | - Shenglong Li
- Department of Bone and Soft Tissue Tumor Surgery, Cancer Hospital of China Medical University, Liaoning Cancer Hospital & Institute, Shenyang, China.,Department of Tissue Engineering, Center of 3D Printing & Organ Manufacturing, School of Fundamental Sciences, China Medical University (CMU), Shenyang, China
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19
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Arai Y, Kiyotsuka Y, Kagechika K, Nishi T, Inui M, Nagamochi M, Oyama K, Izumi M. Discovery of novel, potent, and orally bioavailable pyrido[2,3-d][1]benzazepin-6-one antagonists for parathyroid hormone receptor 1. Bioorg Med Chem 2020; 28:115524. [DOI: 10.1016/j.bmc.2020.115524] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 04/18/2020] [Accepted: 04/20/2020] [Indexed: 10/24/2022]
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20
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G q/11-dependent regulation of endosomal cAMP generation by parathyroid hormone class B GPCR. Proc Natl Acad Sci U S A 2020; 117:7455-7460. [PMID: 32184323 DOI: 10.1073/pnas.1918158117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
cAMP production upon activation of Gs by G protein-coupled receptors has classically been considered to be plasma membrane-delimited, but a shift in this paradigm has occurred in recent years with the identification of several receptors that continue to signal from early endosomes after internalization. The molecular mechanisms regulating this aspect of signaling remain incompletely understood. Here, we investigated the role of Gq/11 activation by the parathyroid hormone (PTH) type 1 receptor (PTHR) in mediating endosomal cAMP responses. Inhibition of Gq/11 signaling by FR900359 markedly reduced the duration of PTH-induced cAMP production, and this effect was mimicked in cells lacking endogenous Gαq/11 We determined that modulation of cAMP generation by Gq/11 occurs at the level of the heterotrimeric G protein via liberation of cell surface Gβγ subunits, which, in turn, act in a phosphoinositide-3 kinase-dependent manner to promote the assembly of PTHR-βarrestin-Gβγ signaling complexes that mediate endosomal cAMP responses. These results unveil insights into the spatiotemporal regulation of Gs-dependent cAMP signaling.
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21
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Liu S, Gellman SH. Preparation of β 2-Homologous Amino Acids Bearing Polar Side Chains via a Collective Synthesis Strategy. J Org Chem 2020; 85:1718-1724. [PMID: 31920080 DOI: 10.1021/acs.joc.9b02562] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
β-Homologous amino acids (βhAAs) are a valuable class of building blocks for novel analogues of bioactive peptides. Thus, practical methods to synthesize enantiopure βhAAs are desirable. We report the application of a collective synthesis strategy to prepare protected β2-homologous amino acids with polar side chains. In this approach, a core structure is constructed via proline-catalyzed Mannich reaction and subsequently derivatized to furnish more than one protected β2-homologous amino acid with a proteinogenic side chain.
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Affiliation(s)
- Shi Liu
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Samuel H Gellman
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
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