Large deletions in the cytoplasmic kinase domain of the epidermal growth factor receptor do not affect its lateral mobility

The lateral diffusion coefficients of various epidermal growth factor (EGF) receptor mutants with increasing deletions in their carboxy-terminal cytoplasmic domain were compared. A full size cDNA construct of human EGF receptor and different deletion constructs were expressed in monkey COS cells. The EGF receptor mutants expressed on the cell surface of the COS cells were labeled with rhodamine-EGF, and the lateral diffusion coefficients of the labeled receptors were determined by the fluorescence photobleaching recovery method. The lateral mobilities of three delection mutants, including a mutant that has only nine amino acids in the cytoplasmic domain, are all similar (D ≃ 1.5 x 10^-10 cm²/s) to the lateral mobility of the 'wild-type' receptor, which possesses 542 cytoplasmic amino acids. It is concluded that most of the cytoplasmic domain of EGF receptor, including its intrinsic protein kinase activity and phosphorylation state, are not required for the restriction of its lateral mobility.