title: Conformational studies of mono- and bicyclic parathyroid hormone-related protein-derived agonists.
abstract: Parathyroid hormone-related protein (PTHrP) is expressed in a wide variety of cells where it acts as an autocrine and/or paracrine factor involved in regulation of cellular growth, differentiation, and embryonic development. It may also play a physiological endocrine role in calcium transport across the placenta or during lactation. The N-terminal portion, PTHrP-(1-34), retains all the calciotropic parathyroid hormone-like activity and is a lead structure for the design of novel, bone anabolic agents for the treatment of bone disorders such as osteoporosis. To characterize the putative bioactive conformation, we have carried out a detailed structural analysis of a series of three conformationally constrained PTHrP-(1-34)-based mono- and bicyclic lactam-containing biologically active analogs: (III) The conformational properties were studied by circular dichroisim, nuclear magnetic resonance spectroscopy, distance geometry calculations, and molecular dynamic simulations in water/trifluoroethanol (TFE) mixtures. The helical content in water of both monocyclic analogs I and II is approximately 22%; that of the bicyclic analog III is approximately 40%. In 30% TFE, all analogs reached a maximal helical content of 80%, corresponding to 26 or 27 residues out of 34 in a helical conformation. High-resolution structures obtained with 50:50 TFE/water revealed that all three analogs display two helical domains and a hinge region around Gly12-Lys13. The highly potent mono- and bicyclic agonists I and III display a second hinge around Arg19-Arg20 which is shifted to Ser14-Asp17 in the weakly potent monocyclic agonist II. We suggest that the presence and localization of discrete hinges in the sequence together with the high propensity for helicity of the C-terminal sequence and the enhancement of helical nucleation at the N-terminal sequence are essential for generating a PTH/PTHrP receptor-compatible bioactive conformation.
authors.affiliation: Department of Pharmacology and Molecular Toxicology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01610, USA. dmierke@black.clarku.edu
authors.forename: D F
authors.initials: DF
authors.lastname: Mierke
authors.forename: S
authors.initials: S
authors.lastname: Maretto
authors.forename: E
authors.initials: E
authors.lastname: Schievano
authors.forename: D
authors.initials: D
authors.lastname: DeLuca
authors.forename: A
authors.initials: A
authors.lastname: Bisello
authors.forename: S
authors.initials: S
authors.lastname: Mammi
authors.forename: M
authors.initials: M
authors.lastname: Rosenblatt
authors.forename: E
authors.initials: E
authors.lastname: Peggion
authors.forename: M
authors.initials: M
authors.lastname: Chorev
mesh_terms: D002942:Circular Dichroism; D003198:Computer Simulation; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010281:Parathyroid Hormone / Q000819:agonists; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000819:agonists / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000819:agonists / Q000737:chemistry* / Q000378:metabolism; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism; D014270:Trifluoroethanol
chemical_list: D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D011506:Proteins; D018016:Receptors, Parathyroid Hormone; C054296:parathyroid hormone-related protein (1-34); D014270:Trifluoroethanol