A Soluble Form of the First Extracellular Domain of Mouse Type 2β Corticotropin-releasing Factor Receptor Reveals Differential Ligand Specificity

Abstract

The heptahelical receptors for corticotropin-releasing factor (CRF), CRFR1 and CRFR2, display different specificities for CRF family ligands: CRF and urocortin I bind to CRFR1 with high affinity, whereas urocortin II and III bind to this receptor with very low affinities. In contrast, all the urocortins bind with high affinities, and CRF binds with lower affinity to CRFR2. The first extracellular domain (ECD1) of CRFR1 is important for ligand recognition. Here, we characterize a bacterially expressed soluble protein, ECD1-CRFR2␤, corresponding to the ECD1 of mouse CRFR2␤. The Corticotropin-releasing factor (CRF) 1 (1) is the major neuroregulator of the hypothalamic-pituitary-adrenal axis and, among other roles, serves to integrate the endocrine, autonomic, and behavioral responses to stress. In addition to its central nervous system actions, CRF and its related ligands also affect the cardiovascular, reproductive, gastrointestinal, skin, and immune systems (2). The CRF ligand family includes (frog) sauvagine, (fish) urotensins, mammalian urocortin I (3, 4), and the 38 amino acid peptides from the newly recognized genes urocortin II (5) and urocortin III (6), also known as stresscopin-related peptide and stresscopin (7).The actions of CRF ligands are initiated by binding to their receptors, whose activation results in an increase of intracellular cAMP, hydrolysis of phosphoinositol, activation of mitogen-activated protein (MAP) kinases (8, 9), and other signaling pathways (10). In mammals, two receptor types, CRFR1 and CRFR2, have been cloned (11-17); orthologous receptors have also been identified in many other species including chicken (18), fish (19), and Xenopus (20). A third receptor, CRFR3, with a high level of sequence identity to CRFR1, has been cloned in catfish (19). CRF receptors have been characterized in the central nervous system and various peripheral sites including pituitary, gastrointestinal tract, epididymis, heart, gonad, adrenal, skin, and skeletal muscle.The CRF receptors are 7-transmembrane domain proteins with relatively large first extracellular domains (ECD1s). Both CRFR1 and CRFR2 exist as multiple splice variants and belong to the type B receptor family that includes receptors for growth hormone-releasing factor, secretin, calcitonin, vasoactive intestinal peptide, glucagon, glucagon-like peptide (GLP), and parathyroid hormone (2).The ligand specificities in binding to CRFR1 and CRFR2 are markedly different. Although both CRF and urocortin I bind with equally high affinities to CRFR1, the affinity of CRF for CRFR2 is at least 10 times lower than that of urocortin I. There is no high affinity interaction of either urocortin II or urocortin III with CRFR1, whereas their affinities for CRFR2 are in the subnanomolar range. The agonist, sauvagine, and the peptide antagonist, astressin, have equally high affinities for both types of receptors (5,6,21).The majority of differences between the sequences of the two receptors are found in their ECD1s. Mutagenesis studies have identified regions o...

Distinct Structural and Functional Roles of Conserved Residues in the First Extracellular Domain of Receptors for Corticotropin-releasing Factor and Related G-protein-coupled Receptors

“…Many studies have shown that the ECD1s of the CRF receptors constitute major ligand-binding sites. Chimeric receptors expressing the ECD1s bind CRF family ligands with high affinity, as do soluble proteins corresponding to the ECD1s (2)(3)(4)(5)(6)(7)(8)(9). Studies of other B1 receptors report similar data (10 -16).…”

Structure of the N-terminal domain of a type B1 G protein-coupled receptor in complex with a peptide ligand

“…1A and SI Table 1). The 3D structure of ECD1-CRF-R2␤ at pH 5 is an SCR motif similar to the fold at pH 7.4 (18) with three disulfide bonds (Cys-45-Cys-70, Cys-60-Cys-103, and Cys-84-Cys-118) (20), and two antiparallel ␤-sheet regions from residues 63-64 (␤1-strand), 70-71 (␤2-strand), 79-82 (␤3-strand), and 99-102 (␤4-strand) (18) (Fig. 1 A).…”

“…However, the binding domain is also crucial for signaling because it controls the binding affinity of the ligand and determines the orientation of the ligand for receptor signaling. Some determinants of binding specificity and affinity are possibly also located in the signaling domains, as suggested by the observation that Ucn 3 and sauvagine bind to CRF-R2␤ with high affinity, but not to the ECD1 of CRF-R2␤ (SI Table 3) (20). It is noteworthy to mention that membrane-peptide interactions seem to be less important in receptor binding (see SI Text).…”

“…Astressin was used as a representative ligand of the CRF family (SI Fig. 6) because it is a very potent peptide antagonist analog (42) and has high binding affinity for both CRF receptors and also their isolated ECD1s (20). The sequential assignment of the ECD1-CRF-R2␤-astressin complex was obtained by assigning the resonances of the 13 C-, 15 N-labeled ECD1-CRF-R2␤ bound to unlabeled astressin and the resonances of astressin with selected residues labeled with 13 C and 15 N bound to unlabeled ECD1-CRF-R2␤ using triple resonance experiments and 3D 15 N-or 13 C-resolved [ 1 H, 1 …”

MALDI-MS analysis of peptides modified with photolabile arylazido groups

“…Two subtypes of CRF receptors have been characterized that exhibit differential affinity for the ligands [6,7]. We have recently identified the first extracellular domain of the CRF type I receptor as playing a major role in agonist and antagonist binding [8,9]. In particular the synthetic peptide antagonist Astressin binds the first extracellular portion with high affinity.…”