Conversion of G-protein specificity of insulin-like growth factor II/mannose 6-phosphate receptor by exchanging of a short region with β- adrenergic receptor

The 14-residue peptide (peptide 14) corresponding to Arg²⁴¹⁰- Lys²⁴²³ of the insulin-like growth factor II receptor (IGF-IIR) can activate the adenylate cyclase-inhibitor guanine nucleotide-binding protein G(i), and the 15-residue βIII-2 peptide Arg²⁵⁹-Lys²⁷³ of the β₂- adrenergic receptor (β₂AR) can activate the stimulatory protein G(s). In phospholipid vesicles, IGF-IIR and β₂AR activate G(i) and G(s) in response to IGF-II and isoproterenol, respectively. We constructed a chimeric IGF-II receptor (βIII-2/IGF-IIR) by converting its native peptide 14 sequence to the βIII-2 sequence. In cells expressing βIII-2/IGF-IIR, membrane adenylate cyclase activity markedly increased without IGF-II and was further promoted by IGF-II. This was verified by measuring chloramphenicol acetyltransferase (CAT) activity in βIII-2/IGF-IIR cells with cotransfection of a cAMP response element-CAT construct. This study shows not only the conversion of G-protein specificity of a receptor from G(i) to G(s) but also the simulation of G protein-coupled receptor signals by using a short receptor region and intact cells. These findings indicate that the G protein-activation signals are interchangeable, self-determined structural motifs that function in the setting of either a single-spanning or multiple-spanning receptor.