A de novo designed signal peptide cleavage cassette functions in vivo.

Leader peptidase (Lep) is a membrane-bound enzyme of the Escherichia coli inner membrane that serves to remove signal peptides from exported proteins. Statistical and experimental studies of known signal peptides have defined a short C-terminal region that seems to provide the information for correct cleavage by Lep. Based on the patterns of conserved amino acids found in this region, we have designed a signal peptide "cleavage cassette." This cassette is processed at the expected site when introduced after an uncleaved signal peptide. Furthermore, processing is blocked in the predicted manner when the (-3, -1)-rule for signal peptide cleavage is violated. This suggests that current understanding of the sequence requirements for signal peptide cleavage is sufficiently advanced to be used in, e.g. protein engineering applications.