title: From molecular details of the interplay between transmembrane helices of the thyrotropin receptor to general aspects of signal transduction in family a G-protein-coupled receptors (GPCRs).
abstract: Transmembrane helices (TMHs) 5 and 6 are known to be important for signal transduction by G-protein-coupled receptors (GPCRs). Our aim was to characterize the interface between TMH5 and TMH6 of the thyrotropin receptor (TSHR) to gain molecular insights into aspects of signal transduction and regulation. A proline at TMH5 position 5.50 is highly conserved in family A GPCRs and causes a twist in the helix structure. Mutation of the TSHR-specific alanine (Ala-593⁵·⁵⁰) at this position to proline resulted in a 20-fold reduction of cell surface expression. This indicates that TMH5 in the TSHR might have a conformation different from most other family A GPCRs by forming a regular α-helix. Furthermore, linking our own and previous data from directed mutagenesis with structural information led to suggestions of distinct pairs of interacting residues between TMH5 and TMH6 that are responsible for stabilizing either the basal or the active state. Our insights suggest that the inactive state conformation is constrained by a core set of polar interactions among TMHs 2, 3, 6, and 7 and in contrast that the active state conformation is stabilized mainly by non-polar interactions between TMHs 5 and 6. Our findings might be relevant for all family A GPCRs as supported by a statistical analysis of residue properties between the TMHs of a vast number of GPCR sequences.
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie, 13125 Berlin, Germany. GKrause@FMP-Berlin.de
authors.forename: Gunnar
authors.initials: G
authors.lastname: Kleinau
authors.forename: Inna
authors.initials: I
authors.lastname: Hoyer
authors.forename: Annika
authors.initials: A
authors.lastname: Kreuchwig
authors.forename: Ann-Karin
authors.initials: AK
authors.lastname: Haas
authors.forename: Claudia
authors.initials: C
authors.lastname: Rutz
authors.forename: Jens
authors.initials: J
authors.lastname: Furkert
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Worth
authors.forename: Gerd
authors.initials: G
authors.lastname: Krause
authors.forename: Ralf
authors.initials: R
authors.lastname: Schülein
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017433:Protein Structure, Secondary; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry* / Q000378:metabolism*; D011989:Receptors, Thyrotropin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D007295:Inositol Phosphates; D043562:Receptors, G-Protein-Coupled; D011989:Receptors, Thyrotropin; D000242:Cyclic AMP