Proteomic amino-termini profiling reveals targeting information for protein import into complex plastids.
In organisms with complex plastids acquired by secondary endosymbiosis from a photosynthetic eukaryote, the majority of plastid proteins are nuclear-encoded, translated on cytoplasmic ribosomes, and guided across four membranes by a bipartite targeting sequence. In-depth understanding of this vital import process has been impeded by a lack of information about the transit peptide part of this sequence, which mediates transport across the inner three membranes. We determined the mature N-termini of hundreds of proteins from the model diatom Thalassiosira pseudonana, revealing extensive N-terminal modification by acetylation and proteolytic processing in both cytosol and plastid. We identified 63 mature N-termini of nucleus-encoded plastid proteins, deduced their complete transit peptide sequences, determined a consensus motif for their cleavage by the stromal processing peptidase, and found evidence for subsequent processing by a plastid methionine aminopeptidase. The cleavage motif differs from that of higher plants, but is shared with other eukaryotes with complex plastids.
Centre for Blood Research and Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada ; Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada.
Pitter F
PF
Huesgen
Meriem
M
Alami
Philipp F
PF
Lange
Leonard J
LJ
Foster
Wolfgang P
WP
Schröder
Christopher M
CM
Overall
Beverley R
BR
Green
D000107:Acetylation; D060365:Chloroplast Proteins / Q000378:metabolism*; D017377:Diatoms / Q000378:metabolism; D018087:Plastids / Q000378:metabolism*; D021381:Protein Transport; D040901:Proteomics / Q000379:methods*
D060365:Chloroplast Proteins