Identification of a region in G protein γ subunits conserved across species but hypervariable among subunit isoforms.

The heterotrimeric GTP binding proteins, G proteins, consist of three distinct subunits: α, β, and γ. There are 12 known mammalian γ subunit genes whose products are the smallest and most variable of the G protein subunits. Sequencing of the bovine brain γ₁₀ protein by electrospray mass spectrometry revealed that it differs from the human protein by an Ala to Val substitution near the N-terminus. Comparison of γ isoform subunit sequences indicated that they vary substantially more at the N-terminus than at other parts of the protein. Thus, species variation of this region might reflect the lack of conservation of a functionally unimportant part of the protein. Analysis of 38 γ subunit sequences from four different species shows that the N-terminus of a given γ subunit isoform is as conserved between different species as any other part of the protein, including highly conserved regions. These data suggest that the N-terminus of γ is a functionally important part of the protein exhibiting substantial isoform-specific variation. [ABSTRACT FROM AUTHOR]