Pmp70

PTS2-bearing matrix protein

Mature peroxisome

Catalase

▲ FIGURE 16-34 Model of peroxisomal biogenesis and division. The first stage in the de novo formation of peroxisomes is the incorporation of peroxisomal membrane proteins into precursor membranes. Pex19 acts as the receptor for membranetargeting sequences. Pex3 and Pex16 are required for the proper insertion of proteins into the forming peroxisomal membrane. Insertion of all peroxisomal membrane proteins produces a peroxisomal ghost, which is capable of importing proteins targeted to the matrix. The pathways for importing PTS1- and PTS2-bearing matrix proteins differ only in the identity of the cytosolic receptor (Pex5 and Pex7, respectively) that binds the targeting sequence (see Figure 16-32). Complete incorporation of matrix proteins yields a mature peroxisome. The proliferation of peroxisomes requires division of mature peroxisomes, a process that depends on the Pex11 protein.

bearing proteins, and then are directed to common import receptor and translocation machinery on the peroxisomal membrane (see Figure 16-32).

■ Translocation of matrix proteins across the peroxisomal membrane depends on ATP hydrolysis. 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, as well as by division of preexisting organelles (see Figure 16-34).

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