Novel features of amphiphilic peptide Mas7 in signalling via heterotrimeric G‐proteins

Amphiphilic peptide Mas7, a structural analogue of mastoparan is a known activator of heterotrimeric G i ‐proteins and its downstream effectors. This study investigated the functional interaction of Mas7 with a plasma membrane protein from CHO cells, the endogenous mono‐ADP‐ribosyltransferase. The substrate of endogenous mono‐ADP‐ribosyltransferase was the ADP‐ribosylated protein with a molecular mass of 36 kDa, which corresponded to the β subunit of heterotrimeric G‐proteins. The effect of Mas7 on endogenous mono‐ADP‐ribosyltransferase activity was in the micromolar range with a maximal activation of 205% over the basal. In pertussis treated plasma membranes, it was found that the effect of Mas7 on endogenous mono‐ADP‐ribosyltransferase was partially blocked, which suggests the involvement of G‐proteins, such as G i or G 0 . In addition, an immunoassay was developed for the visualization of interaction between the α subunit and the βγ dimer of G‐protein on a Ni‐NTA support. The physical interaction was tested of Mas7 with the heterotrimeric G‐protein α i2 subunit, which was overexpressed together with β 1 γ 2 –His 6 subunits in sf9 cells. An interaction between G i2 heterotrimer and Mas7 was not observed, which was not in accordance with previously reported results of mastoparan obtained for G i ‐proteins from bovine brain. In conclusion, the signal is mediated from Mas7 to endogenous mono‐ADP‐ribosyltransferase via pertussis sensitive G‐proteins. Furthermore, it is hypothesized that G i2 G‐proteins are not involved in the process. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd.