The difference in recognition of terminal tripeptides as peroxisomal targeting signal 1 between yeast and human is due to different affinities of their receptor Pex5p to the cognate signal and to residues adjacent to it

Pex5p is the receptor for the peroxisomal targeting signal 1 (PTS1) that co nsists of a C-terminal tripeptide (consensus (S/A/C)(K/R/H)(L/M)). Hexadeca peptides recognized by Pex5p from Homo sapiens and Saccharomyces cerevisiae were identified by screening a two-hybrid peptide library, and the targeti ng ability of the peptides was demonstrated using the green fluorescent pro tein as reporter. The PTS1 receptors recognized in a species-specific manne r a broad range of C-terminal tripeptides, and these are reported herein. I n addition, residues upstream of the tripeptide influenced the strength of the interaction in the two-hybrid system as well as in an in vitro competit ion assay. In peptides interacting with the human protein, hydrophobic resi dues were found with high frequency especially at positions -2 and -5, wher eas peptides interacting with S. cerevisiae Pex5p were more hydrophilic and frequently contained arginine at position -2, In instances where the termi nal tripeptide deviated from the consensus, upstream residues exerted a gre ater influence on the ability of the hexadecapeptides to bind Pex5p.