Efficient chemical synthesis of human complement protein C3a

We report the total chemical synthesis of human C3a by one-pot native chemical ligation of three unprotected peptide segments, followed by efficient in vitro folding that yielded the anaphylatoxin C3a in high yield and excellent purity. Synthetic C3a was fully active and its crystal structure at 2.1 angstrom resolution showed 3 helices and a C-terminal turn motif.