Purity ≥ 90% by SDSPAGE under reducing conditions and visualized by silver stain. Platelet endothelial aggregation receptor 1 (PEAR1) is a 150kD t ype I transmembrane protein and member of the MEGF family of proteins (1). Human PEAR1 is synthesized as a 1037 amino acid (aa) precursor that contains a 20 aa signal sequence, a 735 aa extracellular domain (ECD), a 21 aa transmembrane regi on, and a 261 aa cytoplasmic region (SwissProt #Q5VY43). The ECD consists of 15 EGFlike repeats that vary in length from 39 to 42 aa and contain a consensus sequence of CX 12GX2GX24CX3CX13CX12GX12CX4GX1CX1CX2 GX 2GX2C (1). The consensus repeat contains six conserved glycine residues and eight conserved cysteine residues, suggesting four disulfidebonded cysteine pairs in each EGF repeat(1). Within the ECD, there are also five potential sites f or Nlinked glycosylation. The cytoplasmic r egion contains five potential Src homology 3binding, prolinerich domains (1). Mature human PEAR1 is 84% aa ide