Protein import into chloroplasts involves interactions between precursor proteins and the translocon complex (Toc) located in cell membranes. In 2 January Nature Structural Biology Yuh-Ju Sun and colleagues from Institute of Molecular Biology, Academia Sinica, Taiwan, gave the first details about the Toc34 structure, which provided new insights into the mechanism of protein transport across membranes.

Sun et al. observed the 2 Å resolution crystal structure of the cytosolic component of pea Toc34 in complex with GDP and Mg2+. They found that Toc34 molecules exist as dimers with features resembling those found in a small GTPase in complex with a GTPase activating protein (GAP). In addition, they showed that mutated, monomeric species of Toc34 have a GTPase activity significantly reduced compared to that of wild type Toc34 (Nat Struct Biol 2002, DOI: 10.1038/nsb744).

"These results suggest that each Toc34 monomer acts as a GAP on...

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