The invention provides a mutant of a parent heterotrimeric G protein alpha (Gα) subunit, which mutant (i) lacks at least one helix of the helical domain of the parent Gα subunit; (ii) is capable of binding to a GPCR in the absence of a heterotrimeric G protein beta (Gβ) subunit and a heterotrimeric G protein gamma (Gγ) subunit; and (iii) has an amino acid sequence that contains one or more mutations compared to the amino acid sequence of the parent heterotrimeric Gα subunit, which mutations are selected from a deletion, a substitution and an insertion.

The invention provides a mutant of a parent heterotrimeric G protein alpha (G) subunit, which mutant (i) lacks at least one helix of the helical domain of the parent G subunit; (ii) is capable of binding to a GPCR in the absence of a heterotrimeric G protein beta (G) subunit and a heterotrimeric G protein gamma (G) subunit; and (iii) has an amino acid sequence that contains one or more mutations compared to the amino acid sequence of the parent heterotrimeric G subunit, which mutations are selected from a deletion, a substitution and an insertion.

The invention provides a mutant of a parent heterotrimeric G protein alpha (G?) subunit, which mutant (i) lacks at least one helix of the helical domain of the parent G? subunit; (ii) is capable of binding to a GPCR in the absence of a heterotrimeric G protein beta (G?) subunit and a heterotrimeric G protein gamma (G?) subunit; and (iii) has an amino acid sequence that contains one or more mutations compared to the amino acid sequence of the parent heterotrimeric G? subunit, which mutations are selected from a deletion, a substitution and an insertion.