Functional characterization of the CFTR R domain using CFTR/MDR1 hybrid and deletion constructs

To improve our insight into the structure and function of the CFTR R domain , deletion and hybrid constructs in which different parts of the R domain w ere deleted or replaced by the MDR1 linker domain, and vice versa, were mad e. Replacement of the linker domain by the R domain did not result in a dec rease and replacement of the CFTR R domain by the linker domain did not res ult in an increase of maturation efficiency, when compared to the respectiv e wild-type proteins, This indicates that the R domain is not responsible f or the high degree of degradation observed for CFTR translation products in the ER, but rather the overall structure or sequences located outside the R domain. Replacing the C-terminal part of the R domain (amino acids 780-83 0) by the MDR1 linker domain resulted in the appearance of PKA-dependent wh ole cell chloride currents which were not significantly different from wild -type CFTR currents. This might indicate that the PKA sites present in the linker domain are functional and that not the exact sequence of the C-termi nal part of the R domain is important, but rather the presence of PKA sites and the length. Moreover, when this hybrid construct was PKC-stimulated, c hloride currents were activated, Although these PKC-induced currents were l ower than the PKA-induced ones, this again indicates that the linker domain is functional in this hybrid construct. Taken together, these results sugg est that the MDR1 linker domain can substitute for part of the regulatory d omain of the CFTR protein.