Proton transfer limits protein translocation rate by the thylakoid DeltapH/Tat machinery.
The thylakoid transmembrane DeltapH is the sole energy source driving translocation of precursor proteins by the DeltapH/Tat machinery. Consequently, proton translocation must be coupled to precursor translocation. For the precursor of the 17 kDa protein of the oxygen-evolving complex (pOE17), the protein translocation process is characterized by a steep drop in efficiency at an external pH below 7.0 and above 8.7. As the membrane DeltapH is virtually unaffected from pH 6.5 to 9.2, the loss in import efficiency is a consequence of the titration of multiple residues within the translocation machinery. Transport is retarded by a factor of 2-3 in deuterium oxide (D(2)O) relative to water, strongly suggesting that proton-transfer reactions limit translocation rate. The solvent isotope effect manifests itself after the precursor binds to the membrane, indicating that the rate-limiting step is a later event in the transport process.
Musser
S M
SM
Division of Biological Sciences, Section of Plant Biology, University of California, One Shields Avenue Davis, California 95616, USA.
Theg
S M
SM
D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D003903:Deuterium; D017666:Deuterium Oxide / Q000378:metabolism; D029968:Escherichia coli Proteins; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins; D018532:Pisum sativum / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011522:Protons; D012997:Solvents / Q000737:chemistry; D020524:Thylakoids / Q000378:metabolism*
D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011506:Proteins; D011522:Protons; D012997:Solvents; C408585:twin-arginine translocase complex, E coli; D003903:Deuterium; D017666:Deuterium Oxide