PHOSPHORYLATION SITE INDEPENDENT SINGLE R-DOMAIN MUTATIONS AFFECT CFTR CHANNEL ACTIVITY

We investigated CFTR channel activity of mature R-domain mutants showi ng single alterations at sites other than the predicted phosphorylatio n sites. All mutations mere found in cystic fibrosis (CF) patients (H6 20Q, E822K and E826K), The macroscopic CFTR chloride conductance induc ed by phosphorylation was significantly enhanced in Xenopus oocytes in jected with mRNA of H620Q but reduced in the E822K and E826K mutants c ompared to wild type CFTR. The anion permeability sequence for all thr ee mutants was the same as that of wild type CFTR. Cell attached singl e channel studies in COS cells revealed that both open channel probabi lity and/or the number of functional channels were either higher (H620 Q) or lower (E822K and E826K) than in wild type CFTR. Single channel c onductances were unchanged in all mutants. Our results suggest that ad ditional sites in the R-domain other than phosphorylation sites influe nce gating of CFTR channels. (C) 1998 Federation of European Biochemic al Societies.