Master of Science (MSc)
Faculty of Science
Dr. Matthew D. Smith
Chloroplasts are members of a diverse class of organelles called plastids that differentiate plants from other eukaryotes, and are the site of a number of essential biochemical pathways including photosynthesis. Nuclear-encoded pre-proteins, which account for ~95% of chloroplast proteins, are post-translationally imported into plastids across the double envelope membrane. In the model plant Arabidopsis thaliana, the majority of pre-proteins are imported via the Toc (translocon at outer envelope membrane of chloroplasts) and Tic (translocon at inner envelope membrane of chloroplasts) complexes, the key components of which have been identified. The Toc159 homologues, atToc159 and atToc132/120, have been shown to form structurally and functionally distinct Toc complexes and have been proposed to serve as the primary pre-protein receptors, recognizing and interacting with the N-terminal extensions of pre-proteins, called transit peptides. The tripartite structure of atToc159 includes a membrane anchor (M-) domain, a GTPase (G-) domain, and an acidic (A-) domain that is currently functionally uncharacterized. The A-domain is a large (733 a.a.), intrinsically unstructured protein domain. The sequence identity among Toc159 homologue A-domains is considerably lower than the G- and M-domains. The A-domain has been shown to play a role in the pre-protein specificity exhibited by distinct Toc complexes. In the current study, the A-domain of atToc159 was shown to remain associated with the chloroplast envelope membrane when proteolytically cleaved by thrombin and to interact specifically with the G-domain of atToc159 in vitro. There was not a large change in secondary structure associated with the interaction, as observed by CD, but the interaction between the A- and G-domains of atToc159 was observed to inhibit the hydrolysis of GTP by the G-domain.
Weston, Joseph K., "Toward a functional characterization of the Acidic-domain of the chloroplast protein import receptor Toc159" (2012). Theses and Dissertations (Comprehensive). 838.