NMR and dynamical simulated annealing studies on the solution conformation of urotensin II

Exploring a Structural Data Mining Approach to Design Linkers for Head-to-Tail Peptide Cyclization

Peptides have recently regained interest as therapeutic candidates, but their development remains confronted with several limitations including low bioavailability. Backbone head-to-tail cyclization, i.e., setting a covalent peptide bond linking the last amino acid with the first one, is one effective strategy of peptide-based drug design to stabilize the conformation of bioactive peptides while preserving peptide properties in terms of low toxicity, binding affinity, target selectivity, and preventing enzymatic degradation. Starting from an active peptide, it usually requires the design of a linker of a few amino acids to make it possible to cyclize the peptide, possibly preserving the conformation of the initial peptide and not affecting its activity. However, very little is known about the sequence-structure relationship requirements of designing linkers for peptide cyclization in a rational manner. Recently, we have shown that large-scale data-mining of available protein structures can lead to the precise identification of protein loop conformations, even from remote structural classes. Here, we transpose this approach to linkers, allowing head-to-tail peptide cyclization. First we show that given a linker sequence and the conformation of the linear peptide, it is possible to accurately predict the cyclized peptide conformation. Second, and more importantly, we show that it seems possible to elaborate on the information inferred from protein structures to propose effective candidate linker sequences constrained by length and amino acid composition, providing the first framework for the rational design of head-to-tail cyclization linkers. Finally, we illustrate this for two peptides using a limited set of amino-acids likely not to interfere with peptide function. For a linear peptide derived from Nrf2, the peptide cyclized starting from the experimental structure showed a 26-fold increase in the binding affinity. For urotensin II, a peptide already cyclized by a disulfide bond that exerts a broad array of biological activities, we were able, starting from models of the structure, to design a head-to-tail cyclized peptide, the first synthesized bicyclic 14-residue long urotensin II analogue, showing a retention of in vitro activity. Although preliminary, our results strongly suggest that such an approach has strong potential for cyclic peptide-based drug design.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Structure-activity relationships of urotensin II and URP

Urotensin II (U-II) and urotensin II-related peptide (URP) are the endogenous ligands for the orphan G-protein-coupled receptor GPR14 now renamed UT. At the periphery, U-II and/or URP exert a wide range of biological effects on cardiovascular tissues, airway smooth muscles, kidney and endocrine glands, while central administration of U-II elicits various behavioral and cardiovascular responses. There is also evidence that U-II and/or URP may be involved in a number of pathological conditions including heart failure, atherosclerosis, renal dysfunction and diabetes. Because of the potential involvement of the urotensinergic system in various physiopathological processes, there is need for the rational design of potent and selective ligands for the UT receptor. Structure-activity relationship studies have shown that the minimal sequence required to retain full biological activity is the conserved U-II(4-11) domain, in particular the Cys5 and Cys10 residues involved in the disulfide bridge, and the Phe6, Lys8 and Tyr9 residues. Free alpha-amino group and C-terminal COOH group are not necessary for the biological activity, and modifications of these radicals may even increase the stability of the analogs. Punctual substitution of native amino acids, notably Phe6 and Trp7, by particular residues generates analogs with antagonistic properties. These studies, which provide crucial information regarding the structural and conformational requirements for ligand-receptor interactions, will be of considerable importance for the design of novel UT ligands with increased selectivity, potency and stability, that may eventually lead to the development of innovative drugs.

Urotensin-II receptor peptide agonists

Urotensin II (U-II) has been known for over 30 years as an important teleost fish hormone, but only recently has it been recognized as the endogenous ligand of a new human G-protein-coupled receptor (GPCR) homologous to the GPR14 orphan receptor from rat. Human U-II was found to be a potent vasoconstrictor, widely distributed in human tissues, possibly contributing to several human cardiovascular diseases. It thus has become a major target of medicinal chemistry research. The common structural feature of U-II peptides from different species is the C-terminal portion, characterized by the disulfide bridged cyclic hexapeptide Cys-Phe-Trp-Lys-Tyr-Cys. The few structure-activity relationship studies reported to date attributed a critical role to this portion, with the Trp-Lys-Tyr motif appearing as the key determinant of U-II bioactivity. Consequently, this shorter cyclic peptide was used as a template for the development of several synthetic analogues, among which a superagonist, termed P5U: H-Asp-cyclo(Pen-Phe-Trp-Lys-Tyr-Cys)-Val-OH. Conformational studies confirmed the important role of hU-II C-terminal cyclic portion, enabling the development of 3D pharmacophore models. These findings should lead to the design of new, potent and selective analogues, acting as agonist or antagonist at the human U-II receptor, finally contributing to a deeper comprehension of the (patho)physiological significance of this peptide.

Structure-activity relationships and structural conformation of a novel urotensin II-related peptide

Urotensin II (UII) has been described as the most potent vasoconstrictor peptide and recognized as the endogenous ligand of the orphan G protein-coupled receptor GPR14. Recently, a UII-related peptide (URP) has been isolated from the rat brain and its sequence has been established as H-Ala-Cys-Phe-Trp-Lys-Tyr-Cys-Val-OH. In order to study the structure-function relationships of URP, we have synthesized a series of URP analogs and measured their binding affinity on hGPR14-transfected cells and their contractile activity in a rat aortic ring bioassay. Alanine substitution of each residue of URP significantly reduced the binding affinity and the contractile activity of the peptides, except for the Ala8-substituted analog that retained biological activity. Most importantly, D-scan of URP revealed that [D-Trp4]URP abrogated and [D-Tyr6]URP partially suppressed the UII-evoked contractile response. [Orn5]URP, which had very low agonistic efficacy, was the most potent antagonist in this series. The solution structure of URP has been determined by 1H NMR spectroscopy and molecular dynamics. URP exhibited a single conformation characterized by an inverse gamma-turn comprising residues Trp-Lys-Tyr which plays a crucial role in the biological activity of URP. These pharmacological and structural data should prove useful for the rational design of non-peptide ligands as potential GPR14 agonists and antagonists.

Identification and pharmacological characterization of native, functional human urotensin-II receptors in rhabdomyosarcoma cell lines

1 In an effort to identify endogenous, native mammalian urotensin-II (U-II) receptors (UT), a diverse range of human, primate and rodent cell lines (49 in total) were screened for the presence of detectable [125I]hU-II binding sites. 2 UT mRNA (Northern blot, PCR) and protein (immunocytochemistry) were evident in human skeletal muscle tissue and cells. 3 [(125)I]hU-II bound to a homogenous population of high-affinity, saturable (Kd 67.0+/-11.8 pm, Bmax 9687+/-843 sites cell(-1)) receptors in the skeletal muscle (rhabdomyosarcoma) cell line SJRH30. Radiolabel was characteristically slow to dissociate (< or =15% dissociation 90 min). A lower density of high-affinity U-II binding sites was also evident in the rhabdomyosarcoma cell line TE671 (1667+/-165 sites cell(-1), Kd 74+/-8 pm). 4 Consistent with the profile recorded in human recombinant UT-HEK293 cells, [125I]hU-II binding to SJRH30 cells was selectively displaced by both mammalian and fish U-II isopeptides (Kis 0.5+/-0.1-1.2+/-0.3 nm) and related analogues (hU-II[4-11]>[Cys(5,10)]Acm hU-II; Kis 0.4+/-0.1 and 864+/-193 nm, respectively). 5 U-II receptor activation was functionally coupled to phospholipase C-mediated [Ca2+]i mobilization (EC50 6.9+/-2.2 nm) in SJRH30 cells. 6 The present study is the first to identify the presence of 'endogenous' U-II receptors in SJRH30 and TE671 cells. SJRH30 cells, in particular, might prove to be of utility for (a) investigating the pharmacological properties of hU-II and related small molecule antagonists at native human UT and (b) delineating the role of this neuropeptide in the (patho)physiological regulation of mammalian neuromuscular function.

Photolabelling the rat urotensin II/GPR14 receptor identifies a ligand-binding site in the fourth transmembrane domain

A urotensin II (U-II) peptide analogue containing the photoreactive p -benzoyl-L-phenylalanine (Bz-Phe) in the sixth position was used to identify ligand-binding sites of the rat U-II receptor, also known as GPR14. [Bz-Phe(6)]U-II bound the receptor expressed in COS-7 cells with high affinity (IC(50) 0.7 nM) and was as potent as U-II in the agonist-induced production of inositol phosphate. Photolabelling of the U-II receptor with (125)I-[Bz-Phe(6)]U-II resulted in the specific formation of a glycosylated (125)I-[Bz-Phe(6)]U-II-U-II receptor complex of 60 kDa. Digestion of the 60 kDa complex with endoproteinase Glu-C generated a fragment of 17 kDa circumscribing the labelled fragment to residues 148-286. Digestion of the ligand-receptor complex with endoproteinase Arg-C produced a short peptide of 4 kDa corresponding to fragments 125-148, 167-192 or 210-233. CNBr treatment of the endoproteinase-Glu-C and -Arg-C fragments yielded 2 kDa fragments, defining the labelling site to methionine residues 184/185 of the fourth transmembrane domain. Photolabelling of two mutant receptors, M184L/M185L and M184A/M185A, led to a significant decrease in the overall yield of covalent labelling. Taken together, our results indicate that position 6 of U-II normally occupied by phenylalanine would interact with Met(184) and/or Met(185) of the fourth transmembrane domain of the U-II receptor. This information should be of significant value in the study of the interactions between U-II and its cognate receptor.

Design, synthesis, conformational analysis, and biological studies of urotensin-II lactam analogues

Human urotensin II (hU-II; H-Glu-Thr-Pro-Asp-cyclo[Cys-Phe-Trp-Lys-Tyr-Cys]-Val-OH) is a disulfide bridged undecapeptide recently identified as the ligand of an orphan G protein-coupled receptor. hU-II has been described as the most potent vasoconstrictor compound identified to date. With the aim of replacing the disulfide bridge by a chemically more stable moiety, we have synthesized and tested a series of lactam analogues of hU-II minimum active fragment, that is hU-II(4-11). The contractile activity of the synthetic analogues on the rat isolated thoracic aorta was found to be dependent upon the dimension of the lactam bridge. The most active peptide, H-Asp-cyclo[Orn-Phe-Trp-Lys-Tyr-Asp]-Val-OH (3), is approximately 2 logs less potent than hU-II (pD(2)=6.3 vs 8.4). A conformational analysis in solution of the active peptide 3, one of the inactive analogues, and hU-II was performed, using NMR and molecular modelling techniques. A superposition of the calculated structures of hU-II and 3 clearly shows that three out of four key residues (i.e., Phe(6), Lys(8) and Tyr(9)) maintain the same side- chain orientation, while the fourth one, Trp(7), cannot be superimposed. This observation could explain the reduced biological activity of the synthetic analogue.