Schematic diagram of the conserved WW domain in the juxtamembrane region in native PDGFβR and TEL-PDGFβR fusion, as well as the locations of alanine substitution at conserved tryptophans. (A) Full-length PDGFβR contains an N-terminal extracellular ligand-binding domain, a transmembrane domain (TM), and a split cytoplasmic tyrosine kinase domain (TK). The conserved WW domain is located within the juxtamembrane region between TM and TKs. The sequence alignment of the WW domain in murine and human PDGFβR is shown, with the 2 highly conserved tryptophan residues marked with the stars. The only amino acid difference in this region between the human and murine PDGFβR is boxed. (B) The TEL-PDGFβR fusion variants with distinct alanine substitution at different tryptophan residues. Wild-type TEL-PDGFβR is labeled as WT, TELPDGFβR single mutants are labeled as W566A and W593A, and double mutant W566A/W593A is labeled as WW. All the numbering of mutations is as for native human PDGFβR.