The thionin from Pyrularia pubera (Pp-TH), a 47-residue peptide with four internal disulfide bonds, was efficiently produced by chemical synthesis. Its antimicrobial activity in vitro against several representative pathogens (EC50=0.3–3.0 μM) was identical to that of natural Pp-TH. This peptide has a unique Asp32 instead of the consensus Arg found in other thionins of the same family. In order to evaluate the effect of this mutation, the Arg32 analogue (Pp-TH(D32R)) was also synthesized and showed a significant increase in antibiotic activity against several Gram-negative bacteria, whereas it retained the same activity against other pathogens. The overall structure of Pp-TH(D32R) was maintained, though a slight decrease in the helical content of the peptide was observed.
