Molecular heterogeneity of the beta gamma-subunits of GTP-binding proteins in bovine brain membranes.
The guanine nucleotide-binding proteins (G proteins) are heterotrimers composed of alpha-, beta-, and gamma-subunits, and each of the constituent subunits has been reported to exhibit a molecular heterogeneity. The beta- and gamma-subunits form a functional unit that does not separate under physiological conditions and interact with various alpha-subunits that appear to mainly regulate specific effectors. We thus purified the beta gamma-complex of G proteins from bovine brain membranes and found that there were chromatographically multiple forms of beta gamma-subunits which could be reassociated with various alpha-subunits. The major findings observed with the purified proteins were summarized as follows. (a) The constituent beta gamma-subunits in the brain membrane G proteins appeared to be divided into two groups in their elution profiles from a hydrophobic column. (b) Each of the two groups contained at least five different components of beta gamma-subunits upon analyzing by a high-resolution, anion-exchange column. (c) Distribution of the heterogeneous beta gamma-subunits was not identical among various trimeric G proteins such as Gi, G0, and Gs. (d) The heterogeneous beta gamma-components were able to interact with a specific alpha-subunit resulting in the alpha beta gamma-trimer that served as the substrate of pertussis toxin-catalyzed ADP-ribosylation. (e) However, the apparent abilities of some beta gamma-subunits to support the toxin-induced modification were significantly different in a special comparison between the two beta gamma-groups that were eluted from the hydrophobic column. These results indicated that there were multiple forms of beta gamma-subunits associating with the specific alpha-subunit of a trimeric G protein and that some of those had different affinities for various alpha-subunits in terms of their tight associations. A possible role of the heterogeneity in beta gamma-subunits is also discussed in terms of G protein-mediated signal transductions.
Kontani
K
K
Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
Takahashi
K
K
Inanobe
A
A
Ui
M
M
Katada
T
T
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D046911:Macromolecular Substances; D008970:Molecular Weight; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D046911:Macromolecular Substances; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins