Stimulation of Chloroplast Protein Import By Monovalent Cations
Date Issued
2010
Date
2010
Author(s)
Chang, Jun-Shian
Abstract
Protein translocation across membranes is a fundamental cellular process. The import of proteins into chloroplasts is mediated by translocon components located in the chloroplast outer (the TOC proteins) and inner (the TIC proteins) envelope membranes. Although many translocon components have been identified, the molecular mechanism of the translocation process is not yet clearly understood. Here I found a general stimulation of chloroplast protein translocation caused by NaCl. During import, addition of NaCl in the millimolar level could stimulate the rate of protein import into chloroplasts. The stimulation was not caused by increased osmotic pressure. Furthermore, my data showed that the stimulatory effect was due to monovalent cations like Na+ and K+, not the anion Cl-. NaCl further enhanced the import rate of urea denatured-precursor proteins, suggesting that NaCl stimulation of import rate was not due to the unfolding of precursor proteins. Moreover, NaCl resulted in protein translocation into the stroma at a much lower ATP concentration that normally only supports precursor binding to the chloroplast envelope. These data suggest that NaCl has altered the ATP consumption efficiency during protein translocation.
Subjects
chloroplast
precursor protein
protein import
Type
thesis
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