IDENTIFICATION AND ANALYSIS OF THE PLANT PEROXISOMAL TARGETING SIGNAL-1 RECEPTOR NTPEX5

Protein translocation into peroxisomes takes place via recognition of a peroxisomal targeting signal present at either the extreme C termini (PTS1) or N termini (PTS2) of matrix proteins. In mammals and yeast, the peroxisomal targeting signal receptor, Pex5p, recognizes the PTS1 consisting of -SKL or variants thereof, Although many plant peroxisoma l matrix proteins are transported through the PTSI pathway, little is known about the PTSI receptor or any other peroxisome assembly protein from plants, We cloned tobacco (Nicotiana tabacum) cDNAs encoding Pex 5p (Nt-PEX5) based on the protein's interaction with a PTS1-containing protein in the yeast two-hybrid system, Nucleotide sequence analysis revealed that the tobacco Pex5p contains seven tetratricopeptide repea ts and that NtPEX5 shares greater sequence similarity with its homolog from humans than from yeast. Expression of NtPEX5 fusion proteins, co nsisting of the N-terminal part of yeast Pex5p and the C-terminal regi on of NtPEX5, in a Saccharomyces cerevisiae pex5 mutant restored prote in translocation into peroxisomes, These experiments confirmed the ide ntity of the tobacco protein as a PTSI receptor and indicated that com ponents of the peroxisomal translocation apparatus are conserved funct ionally. Two-hybrid assays showed that NtPEX5 interacts with a wide ra nge of PTS1 variants that also interact with the human Pex5p. Interest ingly, the C-terminal residues of some of these peptides deviated from the established plant PTS1 consensus sequence, We conclude that there are significant sequence and functional similarities between the plan t and human Pex5ps.