Abstract
Toc36 is a family of 44-kDa envelope polypeptides previously identified as components of the chloroplast protein import apparatus by virtue of their close physical proximity to translocating proteins. An indication of their function thus remains at large. A heterologous in vivo approach for studying the function of Toc36 was developed in this study by introducing a member of Toc36 into E. coli to assess its effect on bacterial protein translocation. The presence of Toc36 enhances the translocation of two bacterial periplasmic proteins in a manner resembling the chloroplast system. Translocation of the two bacterial periplasmic proteins was less sensitive to sodium azide, resembling more the azide-insensitive nature of the chloroplast protein import process. Mutated Toc36 proteins were not capable of causing the same effect as that observed for unaltered Toc36. Toc36 was also capable of complementing bacterial strains with temperature-sensitive secA mutations that affected protein translocation. The combined results provide evidence that Toc36 plays a central role in the chloroplast protein translocation process.
Highlights
Nuclear-encoded chloroplast proteins synthesized outside the organelle are imported into the compartment via a complex process
Adaption of the bacterial system for studying the chloroplast envelope protein import apparatus may open up valuable opportunities and features afforded by the bacterial system that can be of assistance for elucidating functional aspects
These results indicate that the bacterial protein translocation machinery recognizes Bce44B, assembling Bce44B with membranes
Summary
Toc is a family of 44-kDa envelope polypeptides previously identified as components of the chloroplast protein import apparatus by virtue of their close physical proximity to translocating proteins. An indication of their function remains at large. Adaption of the bacterial system for studying the chloroplast envelope protein import apparatus may open up valuable opportunities and features afforded by the bacterial system that can be of assistance for elucidating functional aspects This potential was realized by expressing a 44-kDa Toc361 component of the chloroplast envelope protein import apparatus in bacteria [14, 15]. This potential was realized by expressing a 44-kDa Toc361 component of the chloroplast envelope protein import apparatus in bacteria [14, 15]. (The 44kDa components formerly designated Com44/Cim have been renamed in accordance with a newly implemented universal nomenclature)
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