title: Role of amino- and carboxyl-terminal regions of G(alphaZ) in the recognition of Gi-coupled receptors.
abstract: Many Gi-coupled receptors are known to interact with the pertussis toxin (PTX)-insensitive Gz protein. Given that the alpha subunits of Gi and Gz share only 60% identity in their amino acid sequences, their receptor-interacting domains must be highly similar. By swapping the carboxyl termini of alpha i2 and alpha z with each other or with those of alpha t, alpha12, and alpha13, we examined the relative contributions of the carboxyl-end 36 amino acids of the alpha chains toward receptor recognition. Chimeric alpha chains lacking the site for PTX-catalyzed ADP-ribosylation were coexpressed with the type II adenylyl cyclase (AC II) and one of several Gi-coupled receptors (formyl peptide, dopamine D2, and delta-opioid receptors) in human embryonic kidney 293 cells. The alpha i2/alpha z chimera was able to interact with both aminergic and peptidergic receptors, resulting in betagamma-mediated stimulation of AC II in the presence of agonists and PTX. Functional and mutational analyses of alpha i2/alpha z revealed that this chimera can inhibit the endogenous ACs of 293 cells. Similarly, the alpha z/alpha i2 chimera seemed to retain the abilities to interact with receptors and inhibit cAMP accumulation. Fusion of the carboxyl-terminal 36 amino acids of alpha z to a backbone of alpha t1 produced a chimera, alpha t1/alpha z, that did not couple to any of the Gi-coupled receptors tested. Interestingly, an alpha13/alpha z chimera (with only the last five amino acids switched) displayed differential abilities to interact with receptors. Signals from aminergic, but not peptidergic, receptors were transduced by alpha13/alpha z. A similar construct, alpha12/alpha z, behaved just like alpha13/alpha z. These results indicated that "alpha i-like" or "alpha z-like" sequences at the carboxyl termini of alpha subunits are not always necessary or sufficient for specifying interaction with Gi-coupled receptors.
authors.affiliation: Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon.
authors.forename: R C
authors.initials: RC
authors.lastname: Tsu
authors.forename: M K
authors.initials: MK
authors.lastname: Ho
authors.forename: L Y
authors.initials: LY
authors.lastname: Yung
authors.forename: S
authors.initials: S
authors.lastname: Joshi
authors.forename: Y H
authors.initials: YH
authors.lastname: Wong
mesh_terms: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D037342:Pertussis Toxin; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000378:metabolism; D018000:Receptors, Peptide / Q000378:metabolism; D013329:Structure-Activity Relationship; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D004745:Enkephalins; D011956:Receptors, Cell Surface; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic; D017465:Receptors, Opioid, delta; D018000:Receptors, Peptide; D010566:Virulence Factors, Bordetella; D020881:Enkephalin, D-Penicillamine (2,5)-; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins