title: Arrangement of transmembrane domains in adrenergic receptors. Similarity to bacteriorhodopsin.
abstract: G protein-coupled receptors (GPCRs) have seven hydrophobic domains, which are thought to span the lipid bilayer as alpha helical transmembrane domains (TMDs). The tertiary structure of GPCRs has not been determined; however, molecular models of GPCRs have generally been based on bacteriorhodopsin, which is functionally unrelated to GPCRs but has a similar secondary structure. We sought to examine the validity of using bacteriorhodopsin as a scaffold for GPCR model building by experimentally determining the orientation of the TMDs of adrenergic receptors in the plasma membrane. In separate experiments, three sequential amino acid residues (Leu-310, Leu-311, Asn-312) in TMD VII of the beta 2 adrenoreceptors were mutated to the amino acids found in the homologous domain of the alpha 2 adrenoceptor (Phe, Phe, Phe). Exchange of Asn-312 and Leu-311 in the beta 2 adrenoceptor resulted in nonfunctional proteins, most likely due to incompatibility of the introduced bulky phenylalanine side chain with adjacent structural domains in the beta 2 adrenoreceptor. This structural incompatibility was "repaired" by replacing the specific beta 2 TMD sequence with an alpha 2 receptor sequence. TMD I and TMD II complemented the Asn-312-->Phe mutation, and TMD III and TMD VI complemented the Leu-311-->Phe mutation. These results indicate that TMDs I, II, III, and VI surround TMD VII in a counter-clockwise orientation analogous to the orientation of TMDs in bacteriorhodopsin.
authors.affiliation: Department of Anesthesia, Stanford University, California 94305, USA.
authors.forename: T
authors.initials: T
authors.lastname: Mizobe
authors.forename: M
authors.initials: M
authors.lastname: Maze
authors.forename: V
authors.initials: V
authors.lastname: Lam
authors.forename: S
authors.initials: S
authors.lastname: Suryanarayana
authors.forename: B K
authors.initials: BK
authors.lastname: Kobilka
mesh_terms: D000818:Animals; D001436:Bacteriorhodopsins / Q000737:chemistry*; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D018341:Receptors, Adrenergic, alpha-2; D018343:Receptors, Adrenergic, beta-2; D001436:Bacteriorhodopsins