Targeting of thylakoid proteins by the delta pH-driven twin-arginine translocation pathway requires a specific signal in the hydrophobic domain in conjunction with the twin-arginine motif.
Superficially similar cleavable targeting signals specify whether lumenal proteins are transported across the thylakoid membrane by a Sec- or delta pH-dependent pathway. A twin-arginine motif is essential but not sufficient to direct delta pH-dependent targeting; here we show that a second determinant is located in the hydrophobic region. A highly hydrophobic amino acid is found either two or three residues C-terminal to the twin-arginine in all known transfer peptides for the delta pH-dependent system, and substitution of this residue in the 23-kDa (23K) peptide markedly inhibits translocation. Further, whereas the insertion of twin-arginine in a Sec-dependent precursor does not permit efficient delta pH-dependent targeting, the simultaneous presence of a leucine at the +3 position (relative to the RR) enables the peptide to function as efficiently as an authentic transfer peptide. RRNVL, RRAAL and RRALA within a Sec targeting signal all support efficient delta pH-dependent targeting, RRNVA is less effective and RRNAA/RRNAG are totally ineffective. We conclude that the core signal for this pathway is a twin-arginine together with an adjacent hydrophobic determinant.
Brink
S
S
Department of Biological Sciences, University of Warwick, Coventry, UK.
Bogsch
E G
EG
Edwards
W R
WR
Hynds
P J
PJ
Robinson
C
C
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D001120:Arginine / Q000378:metabolism*; D001692:Biological Transport; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D021382:Protein Sorting Signals / Q000737:chemistry / Q000378:metabolism*
D008565:Membrane Proteins; D021382:Protein Sorting Signals; D001120:Arginine