title: Different lumen-targeting pathways for nuclear-encoded versus cyanobacterial/plastid-encoded Hcf136 proteins.
abstract: Lumenal proteins are transported across the thylakoid membrane by two very different pathways: Sec-dependent or twin-arginine translocase (Tat)-dependent, where the substrate protein can be transported in a folded state. We present the first evidence that a given protein can be targeted by different pathways in different organisms. Arabidopsis Hcf136 is targeted exclusively by the Tat pathway in pea chloroplasts and no Sec-dependent transport is evident even when the twin-arginine is replaced by twin-lysine. However, twin-arginine motifs are absent from the presequences of Hcf136 proteins encoded by plastid or cyanobacterial genomes, strongly implying translocation by another pathway (presumably Sec). We suggest that the Hcf136 protein was transferred to the Tat pathway when the gene became incorporated into the nuclear genome, possibly due to the tighter folding associated with the more involved, post-translational targeting pathway.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hynds
authors.forename: H
authors.initials: H
authors.lastname: Plücken
authors.forename: P
authors.initials: P
authors.lastname: Westhoff
authors.forename: C
authors.initials: C
authors.lastname: Robinson
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins; D005075:Biological Evolution; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D000458:Cyanobacteria / Q000166:cytology* / Q000235:genetics; D029968:Escherichia coli Proteins; D056890:Eukaryota / Q000166:cytology / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000201:enzymology / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000166:cytology* / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D021382:Protein Sorting Signals / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D020524:Thylakoids / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C115034:HCF136 protein, Arabidopsis; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; D001120:Arginine; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins