Receptor Structure and Function

Thursday, May 18th, 2006 at 13:00 in Benzon Auditorium

The Danish University of Pharmaceutical Sciences Universitetsparken 2, 2100 Copenhagen O

The workshop is organised by: Jette Sandholm Kastrup (the Danish University of Pharmaceutical Sciences) and is open for attendance by all interested parties.

Rob Leurs,

Leiden/Amsterdam Center for Drug Research, Division of Medicinal Chemistry, Vrije Universiteit Amsterdam, The Netherlands.

leurs@few.vu.nl

Using a combination of molecular modeling and protein mutagenesis we try to investigate basic mechanisms of G-protein coupled receptor (GPCR) function, i.e. ligand binding and GPCR activation. In aminergic GPCRs, including the histamine H1 receptor (H1R), the ligand-binding pocket is thought to reside in a hydrophilic cleft formed by the seven transmembrane domains (TMs). Small molecule binding to the aminergic receptors is currently considered to mainly occur between the TMs 3 (containing the conserved an aspartate (Asp), 5 and 6. Using the natural variation in GPCR sequence we recently obtained evidence that for some H1R ligands, the binding pocket is not only limited to TMs 3, 5, and 6 but also comprises an additional pocket formed by TMs 2 and 7, that is not targeted by most developed H1 antagonists.

The detailed molecular mechanism for agonist-induced activation of rhodopsin-like GPCRs has not yet been described. Activation of GPCRs is thought to involve disruption of intramolecular interactions that stabilize their inactive conformations. Such disruptions are induced by agonists but may also be induced upon mutation of the receptor. Recently, we characterized important steps in the activation of H1R. Both Ser3.36 and Asn7.45 are important links between histamine binding and previously proposed conformational changes in helices 6 and 7. Ser3.36 acts as a rotamer toggle switch that, upon agonist binding, initiates the activation of the receptor through Asn7.45. The proposed transduction involves specific residues that are conserved among rhodopsin-like GPCRs. To further investigate the activation process of the rhodopsin-like family of GPCRs we created (through random mutagenesis) and characterized constitutively active mutant histamine H1 receptors. Several highly constitutive active mutants were obtained and their action can be rationalized by the existence of a conserved hydrophobic motif in the TM pocket, which is stabilizing the inactive receptor state.

Vladimir Berezin,

The Panum Institute, University of Copenhagen, Denmark

The neural cell adhesion molecule NCAM plays a pivotal role during development of the nervous system, mediating binding between neural cells and stimulating neurite outgrowth and fasciculation. In adult brain NCAM regulates synaptic plasticity, including such processes as learning and memory consolidation. Recently, the role of NCAM in neuroprotection has been proposed. NCAM is a multiligand signaling receptor involved in homophilic binding to itself and in heterophilic interactions with a variety of components of the extracellular matrix, other cell adhesion molecules, glial-cell-line derived neurotrophic factor (GDNF) and its receptor (GFRα), and fibroblast growth factor (FGF) receptor. Recent advances in understanding the structural basis for the NCAM homophilic binding and activation of the FGF-receptor followed by identification of a number of NCAM mimetic peptides constitute a breakthrough in pharmacological approaches both as regards the study of the role of NCAM in synaptic plasticity and neuroprotection and as regards development of treatment for neurodegenerative disorders.