The human calcitonin family peptide hormones calcitonin (CT), amylin (Amy), calcitonin-gene related peptide (CGRP), adrenomedullin (AM), and adrenomedullin 2/intermedin (AM2/IMD) exhibit diverse actions including regulation of bone remodeling (CT), vasodilation and cardioprotection (CGRP, AM, AM2/IMD), and regulation of blood glucose and food intake (Amy) by activating the cell surface class B G protein-coupled receptors (GPCRs) calcitonin receptor (CTR) and calcitonin-like receptor (CLR). Three receptor activity-modifying proteins (RAMP1-3) heterodimerize with CLR and CTR and determine their peptide preferences. The seven resulting receptors (six heterodimers and CTR alone) are proven or promising drug targets for diseases that are a significant burden on human health including migraine headache (CGRP receptor; CLR:RAMP1), diabetes and obesity (Amy receptors; CTR:RAMP1/2/3), osteoporosis (CT receptor; CTR), and cardiovascular disorders (AM receptors; CLR:RAMP2/3). These complex receptors are a paradigm for modulation of GPCR pharmacology by accessory membrane proteins, but our understanding of their selective peptide recognition mechanisms and distinct biological functions is incomplete. Our structural studies have highlighted the critical role of the receptor extracellular domains (ECDs) for peptide selectivity and provided important insights into how RAMP1 and RAMP2 alter CLR selectivity for CGRP and AM. Herein we continue to investigate the mechanisms by which RAMPs modulate CLR and CTR. We will test the hypothesis that allosteric modulation of CLR conformation by RAMPs is important for selectivity and based on our discovery that CTR N- glycosylation enhances its peptide affinity 10-fold we will test the hypothesis that this effect is also allosteric in nature. We will fill critical gaps in our knowledge by providing crystal structures of AM2/IMD, CT, and Amy bound to their receptor ECD complexes. We use biochemical, pharmacological, and X-ray crystallographic approaches for each of the specific aims.
In Aim 1 we will probe the role of allostery in RAMP-altered CLR peptide selectivity through the use of novel altered selectivity antagonist CGRP and AM variants developed through rational design and screening of synthetic peptide combinatorial libraries.
In Aim 2 we will determine how AM2/IMD binds CLR:RAMP1 and CLR:RAMP3 ECD complexes and how RAMP3 modulates CLR.
In Aim 3 we will define how RAMPs and N-glycosylation of CTR ECD modulate CT and Amy binding. Successful completion of this project will lead to the following outcomes: 1) a better understanding of how each of the CT family peptides bind their receptors, 2) delineation of the role of allostery in RAMP function, 3) elucidation of the mechanisms by which N-glycans and RAMPs modulate CTR peptide binding, and 4) development of novel peptide antagonists with enhanced affinities and altered selectivities that may be of value as pharmacological tools for interrogating receptor biology and may inform drug development targeting the receptors.

Public Health Relevance

This project uses powerful structural biology, biochemistry, and pharmacology techniques to elucidate how calcitonin family peptide hormones bind to their receptors on the surface of cells and develop novel tools for studying the receptors. The hormones regulate bone remodeling, vascular tone, blood glucose, and food intake and the receptors are drug targets for diseases including osteoporosis, migraine headache, cardiovascular disorders, and diabetes and obesity. Our studies will facilitate the development of therapeutics targeting these receptors and reveal concepts that are broadly relevant for several areas of human health and disease because the receptors are members of the large GPCR family that regulates many aspects of physiology.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular and Integrative Signal Transduction Study Section (MIST)
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Koduri, Sailaja
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University of Oklahoma Health Sciences Center
Schools of Medicine
Oklahoma City
United States
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Booe, Jason M; Warner, Margaret L; Roehrkasse, Amanda M et al. (2018) Probing the Mechanism of Receptor Activity-Modifying Protein Modulation of GPCR Ligand Selectivity through Rational Design of Potent Adrenomedullin and Calcitonin Gene-Related Peptide Antagonists. Mol Pharmacol 93:355-367
Roehrkasse, Amanda M; Booe, Jason M; Lee, Sang-Min et al. (2018) Structure-function analyses reveal a triple ?-turn receptor-bound conformation of adrenomedullin 2/intermedin and enable peptide antagonist design. J Biol Chem 293:15840-15854
Lee, Sang-Min; Booe, Jason M; Gingell, Joseph J et al. (2017) N-Glycosylation of Asparagine 130 in the Extracellular Domain of the Human Calcitonin Receptor Significantly Increases Peptide Hormone Affinity. Biochemistry 56:3380-3393
Hay, Debbie L; Pioszak, Augen A (2016) Receptor Activity-Modifying Proteins (RAMPs): New Insights and Roles. Annu Rev Pharmacol Toxicol 56:469-87
J Gingell, Joseph; Simms, John; Barwell, James et al. (2016) An allosteric role for receptor activity-modifying proteins in defining GPCR pharmacology. Cell Discov 2:16012
Watkins, Harriet A; Chakravarthy, Madhuri; Abhayawardana, Rekhati S et al. (2016) Receptor Activity-modifying Proteins 2 and 3 Generate Adrenomedullin Receptor Subtypes with Distinct Molecular Properties. J Biol Chem 291:11657-75
Lee, Sang-Min; Hay, Debbie L; Pioszak, Augen A (2016) Calcitonin and Amylin Receptor Peptide Interaction Mechanisms: INSIGHTS INTO PEPTIDE-BINDING MODES AND ALLOSTERIC MODULATION OF THE CALCITONIN RECEPTOR BY RECEPTOR ACTIVITY-MODIFYING PROTEINS. J Biol Chem 291:8686-700
Booe, Jason M; Walker, Christopher S; Barwell, James et al. (2015) Structural Basis for Receptor Activity-Modifying Protein-Dependent Selective Peptide Recognition by a G Protein-Coupled Receptor. Mol Cell 58:1040-52
Lee, Sang-Min; Booe, Jason M; Pioszak, Augen A (2015) Structural insights into ligand recognition and selectivity for classes A, B, and C GPCRs. Eur J Pharmacol 763:196-205
Warner, Margaret L; Bell, Tufica; Pioszak, Augen A (2015) Engineering high-potency R-spondin adult stem cell growth factors. Mol Pharmacol 87:410-20

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