G protein βγ subunits from bovine brain and retina: Equivalent catalytic support of ADP-ribosylation of α subunits by pertussis toxin but differential interactions with G

Patrick J. Casey, Michael P. Graziano, Alfred G. Gilman

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Abstract

We have examined the ability of the βγ subunits of guanine nucleotide binding regulatory proteins (G proteins) to support the pertussis toxin (PT) catalyzed ADP-ribosylation of G protein α subunits. Substoichiometric amounts of the βγ complex purified from either bovine brain G proteins or the bovine retinal G protein, Gt, are sufficient to support the ADP-ribosylation of the α subunits of Gi (the G protein that mediates inhibition of adenylyl cyclase) and Go (a G protein of unknown function) by PT. This observation indicates that ADP-ribosylated G protein oligomers can dissociate into their respective α and βγ subunits in the absence of activating regulatory ligands, i.e., nonhydrolyzable GTP analogues or fluoride. Additionally, the catalytic support of ADP-ribosylation by bovine brain βγ does not require Mg2+. Although the βγ subunit complexes purified from bovine brain G proteins and the βγ complex of Gt support equally the ADP-ribosylation of a subunits by PT, there is a marked difference in their abilities to interact with G. The enhancement of deactivation of fluoride-activated G requires 25-fold more βγ from Gt than from brain G proteins to produce a similar response. This difference in potency of βγ complexes from the two sources was also observed in the ability of βγ to produce an increase in the activity of recombinant G produced in Escherichia coli.

Original languageEnglish (US)
Pages (from-to)611-616
Number of pages6
JournalBiochemistry
Volume28
Issue number2
Publication statusPublished - 1989

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ASJC Scopus subject areas

  • Biochemistry

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