PTS1-independent targeting of isocitrate lyase to peroxisomes requires the PTS1 receptor Pex5p.
The targeting of castor bean isocitrate lyase to peroxisomes was studied by expression in the heterologous host Saccharomyces cerevisae from which the endogenous ICL1 gene had been removed by gene disruption. Peroxisomal import of ICL was dependent upon the PTS1 receptor Pex5p and was lost by deletion of the last three amino acids, Ala-Arg-Met. However, removal of an additional 16 amino acids restored the ability of this truncated ICL to be targeted to peroxisomes and this import activity, like that of the full-length protein, was dependent upon Pex5p. The ability of peptides corresponding to the carboxyl terminal ends of wild-type and Delta 3 and Delta 19 mutants of ICL to interact with the PTS1-binding portion of Pex5p from humans, plants and yeast was determined using the yeast two-hybrid system. The peptide corresponding to wild-type ICL interacted with all three Pex5p proteins to differing extents, but neither mutant could interact with Pex5p from any species. Thus, ICL can be targeted to peroxisomes in a Pex5p-dependent but PTS1-independent fashion. These results help to clarify the contradictory published data about the requirement of the PTS1 signal for ICL targeting.
Centre for Plant Sciences University of Leeds LS2 9JT Leeds, UK.
John A
JA
Parkes
Sigrid
S
Langer
Andreas
A
Hartig
Alison
A
Baker
D000595:Amino Acid Sequence; D001483:Base Sequence; D002367:Ricinus communis / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D007522:Isocitrate Lyase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D000074437:Peroxisomal Targeting Signal 2 Receptor; D000074435:Peroxisome-Targeting Signal 1 Receptor; D020675:Peroxisomes / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D010455:Peptides; D000074437:Peroxisomal Targeting Signal 2 Receptor; D000074435:Peroxisome-Targeting Signal 1 Receptor; D010940:Plant Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; C542285:ICL1 protein, S cerevisiae; D007522:Isocitrate Lyase