Diversity and Design Principles of Transit Peptide, Chloroplast Targeting Signal

Chloroplast is a subcellular organelle uniquely present in plant kingdom, and is responsible for the photosynthesis. Considering its endosymbiotic origin, chloroplast has its own genome. However, the majority of chloroplast proteins is encoded in the nuclear genome and postranslationally targeted to chloroplasts. Most chloroplast interior proteins possess the N-terminal transit peptide, a chloroplast targeting signal, which is necessary and sufficient for delivering any client proteins to the interior region of chloroplasts. One hallmark of transit peptides is their extreme diversity. On the other hand, the mechanisms for protein import into chloroplasts are very limited. In this review, I will recapitulate the physicochemical properties and domain organization of diverse transit peptides, and discuss how limited import machineries can accommodate chloroplast proteins with diverse transit peptides. Additional key words: Transit peptide, Chloroplast, Protein import, Domain structure, Sequence motifs