The Mid-Region of Parathyroid Hormone (1-34) Serves as a Functional Docking Domain in Receptor Activation

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• 作者：Angela Wittelsberger ; Martina Corich ; Beena E. Thomas ; Byung-Kwon Lee ; Alessandra Barazza ; Paul Czodrowski ; Dale F. Mierke ; Michael Chorev ; and Michael Rosenblatt
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：February 21, 2006
• 年：2006
• 卷：45
• 期：7
• 页码：2027 - 2034
• 全文大小：276K
• 年卷期：v.45,no.7(February 21, 2006)
• ISSN：1520-4995

文摘

Elucidating the bimolecular interface between parathyroid hormone (PTH) and its cognate Gprotein-coupled receptor (PTHR1) should yield insights into the basis of molecular recognition and themechanism of ligand-mediated intracellular signaling for a system that is critically important in regulatingcalcium levels in blood. We used photoaffinity scanning (PAS) to identify key ligand-receptor interactionsfor residues from the unstructured mid-region domain of PTH-(1-34). Four PTH analogues, containinga single photoreactive p-benzoylphenylalanine (Bpa) residue in position 11, 15, 18, or 21, were found tophoto-cross-link within receptor regions [165-176], [183-189], [190-298], and [165-176], respectively.Addition of these mid-region contacts as constraints to our previously proposed model of the PTH-PTHR1 complex and extensive molecular simulation experiments enables substantial refinement of themodel. Specifically, (1) the overall receptor-bound conformation of the hormone is not extended, butbent; (2) helix [169-176] of the N-terminal extracellular domain (N-ECD) of the receptor is redirectedtoward the heptahelical bundle; and (3) the hormone traverses between the top of transmembrane (TM)helices 1 and 2, rather than between TM-7 and TM-1. This significantly alters the model of both thereceptor-bound tertiary structure of the hormone and the topological orientation of the C-terminus of theN-ECD in the hormone-receptor bimolecular complex. We propose that the mid-region of PTH-(1-34)has a role in fixing, by extensive contacts with the receptor, the entry of the N-terminal helix of thehormone into the heptahelical bundle between TM-1 and TM-2. This anchorage would orient the aminoterminus into position to activate the receptor.