title: The paradox of plastid transit peptides: conservation of function despite divergence in primary structure.
abstract: Transit peptides are N-terminal extensions that facilitate the targeting and translocation of cytosolically synthesized precursors into plastids via a post-translational mechanism. With the complete Arabidopsis genome in hand, it is now evident that transit peptides direct more than 3500 different proteins into the plastid during the life of a typical plant. Deciphering a common mechanism for how this multitude of targeting sequences function has been hampered by the realization that at a primary sequence level, transit peptides are highly divergent in length, composition, and organization. This review addresses recent findings on several of the diverse functions that transit peptides must perform, including direct interaction with envelope lipids, association with a cis-acting guidance complex, recognition by envelope receptors, insertion into the Toc/Tic translocon, interaction with molecular motors, and finally, recognition/cleavage by the stromal processing peptidase. In addition to higher plants, transit peptides also direct the import of proteins into complex plastids derived from secondary endosymbiosis. An emerging concept suggests that transit peptides contain multiple domains that provide either distinct or possibly overlapping functions. Although still poorly characterized, evolutionary processes could yield transit peptides with alternative domain organizations.
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, Center of Excellence in Structural Biology, Graduate Program in Genome Science and Technology, University of Tennessee, Knoxville, TN 37917, USA. bbruce@utk.edu
authors.forename: B D
authors.initials: BD
authors.lastname: Bruce
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism*; D017377:Diatoms / Q000235:genetics; D019143:Evolution, Molecular; D018745:Genome, Plant; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D020409:Molecular Motor Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000502:physiology*; D021381:Protein Transport; D013329:Structure-Activity Relationship
chemical_list: D060365:Chloroplast Proteins; D020409:Molecular Motor Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; C078737:chloroplast transit peptides