Scientists Explain the Molecular Basis for Channels of Protein Import into Chloroplasts of Arabidopsis

Translocon is a complex of proteins responsible for the transfer of polypeptides across membranes. The translocons at the outer envelope membrane of chloroplasts (TOCs) instigate the import of thousands of nucleus-encoded proteins into the chloroplast. Studies regarding the structure and function of the different TOC complexes have led to the hypothesis that the translocons are involved in various protein import channels, wherein the expression of those proteins depends on the organelle formation and physiological adaptation. Hitoshi Inoue, scientist at the University of Massachusetts, and colleagues tested this hypothesis by analyzing the differences in the function of the Toc159 family of receptors at the molecular level.

The Toc159 family members have three structural domains: a C-terminal membrane anchor domain (M-domain), a central GTPase domain (G-domain), and a highly acidic N-terminal domain (A-domain). Results showed that the A-domains control the selection of protein prior to binding. Moreover, the functions of the two major Toc159 family members can be interchanged by swapping their A-domains in transgenic Arabidopsis thaliana. The scientists propose that the A-domains of the Toc-159 receptors determine the channels for import of proteins into chloroplasts.

Subscribers of The Plant Cell Journal can read the full article at http://www.plantcell.org/cgi/content/full/22/6/1947.