Single Amino Acid of Gα16 (Ala228) Is Responsible for the Ability of Chemoattractant C5a Receptor to Induce Gα16-Mediated Inositol Phosphate Release

Abstract

Our previous study suggested that the region encompassing residues 220–240 on Gα16 is important in coupling with C5a receptor (Lee et al. (1995) Mol. Pharmacol. 47, 218–223). When aligned sequences are compared in the residue 220–240 segment of Gα16, there is a block of eight amino acids extending from residue 227 to residue 234 (227-Ile-Ala-Leu-Ile-Tyr-Leu-Ala-Ser-234) in Gα16 that is replaced by a heterologous block extending from amino acid residue 224 to residue 231 (224-Thr-Ser-Ile-Met-Phe-Leu-Val-Ala-231) in Gα11. In order to identify the specific amino acid residue necessary for coupling to C5a receptor within the extension of eight amino acids in Gα16, a series of chimeric Gα11/Gα16 cDNA constructs and mutant Gα16 cDNAs were expressed. Then the ability of chimeras and mutant proteins to mediate C5a-induced release of inositol phosphate in transfected Cos-7 cells was tested. The results show that single amino acid Ala228 is responsible for conferring about 40–50% of the activity of Gα16 induced by C5a receptor stimulation.