Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 3, Pages 930-935Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1115886110
Keywords
translocation ATPase; chloroplast translocons at inner and outer envelop membranes; import machineries; protein trafficking; cellular energy budget
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Funding
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy [DE-FG02-03ER15405]
- U.S. Department of Energy (DOE) [DE-FG02-03ER15405] Funding Source: U.S. Department of Energy (DOE)
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Chloroplasts are the organelles of green plants in which light energy is transduced into chemical energy, forming ATP and reduced carbon compounds upon which all life depends. The expenditure of this energy is one of the central issues of cellular metabolism. Chloroplasts contain similar to 3,000 proteins, among which less than 100 are typically encoded in the plastid genome. The rest are encoded in the nuclear genome, synthesized in the cytosol, and posttranslationally imported into the organelle in an energy-dependent process. We report here a measurement of the amount of ATP hydrolyzed to import a protein across the chloroplast envelope membranes-only the second complete accounting of the cost in Gibbs free energy of protein transport to be undertaken. Using two different precursors prepared by three distinct techniques, we show that the import of a precursor protein into chloroplasts is accompanied by the hydrolysis of similar to 650 ATP molecules. This translates to a Delta G(protein transport) of some 27,300 kJ/mol protein imported. We estimate that protein import across the plastid envelope membranes consumes similar to 0.6% of the total light-saturated energy output of the organelle.
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