Key Concepts of Section 13.5

• All luminal peroxisomal proteins are synthesized on free cytosolic ribosomes and incorporated into the organelle post-translationally.

• Most peroxisomal matrix proteins contain a C-terminal targeting sequence known as PTS1; a few have an N-terminal PTS2 targeting sequence. Neither targeting sequence is cleaved after import.

• All proteins destined for the peroxisomal matrix bind to a cytosolic receptor protein, which differs for PTS1- and PTS2-bearing proteins, and then are directed to common translocation machinery on the peroxisomal membrane (see Figure 13-30).

• Translocation of matrix proteins across the peroxisomal membrane depends on ATP hydrolysis. Unlike proteins imported to the ER, mitochondrion, or chloroplast, many peroxisomal matrix proteins fold in the cytosol and traverse the membrane in a folded conformation.

• Proteins destined for the peroxisomal membrane contain different targeting sequences than peroxisomal matrix proteins and are imported by a different pathway.

• Unlike mitochondria and chloroplasts, peroxisomes can arise de novo from precursor membranes derived from the ER as well as by division of preexisting organelles (see Figure 13-32).