Fig. 2. The CT of synaptotagmin VII can be internalized in a tryptophan-dependent manner. (A) The CD4-CT constructs of synaptotagmin I (residues 393-421, CT 1) and synaptotagmin VII (387-403, CT 7) were tested for their ability to be endocytosed in PC12 cells using the previously described internalization assay. (B) When the tryptophan residue with the C-terminal WHXL is mutated to an alanine in either CT1 (W404A) or CT 7 (W398A), the internalization in PC12 cells is abolished.