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Danny J. Schnell

Professor, Graduate Program Director


LSL N431
(413) 545-4024


Mechanisms of protein import into the plant chloroplast, Protein targeting, Organelle biogenesis

Background and Training

Ph.D: University of California
Postdoctoral training: Rockefeller University, New York

Research Summary

The long-term goal of our research is to understand the mechanism of protein import into plant chloroplasts as a model for protein targeting and organelle biogenesis in eukaryotic cells. 

Organelle identity and development rely on a complex set of intracellular protein trafficking systems that mediate the specific targeting of nuclear-encoded proteins to their proper subcellular compartment. Although protein targeting systems have been described for all organelles, the mechanisms of signal recognition and protein translocation at boundary membranes remain major topics of investigation in cell biology. We have identified a set of chloroplast membrane proteins, the Toc and Tic proteins, that recognize and transport nuclear-encoded proteins into chloroplasts.

We are using protein biochemical and cell biological techniques to define the activities of individual Toc/Tic components with the aim of understanding how these complexes selectively recognize chloroplast proteins and transport them across the double-membrane of the chloroplast envelope. A second major goal of our studies is to understand the role of protein import in the development of plants, specifically the process by which plants acquire photosynthetic competence. These studies incorporate molecular genetic techniques in Arabidopsis thaliana to investigate the diversity of Toc-Tic complexes and define the roles of these complexes in the selective import of proteins at different developmental stages.


Inoue H, Wang F, Inaba T, Schnell DJ. 2011. Energetic manipulation of chloroplast protein import and the use of chemical cross-linkers to map protein-protein interactions. Methods Mol Biol.774:307-20. [PubMed]

Oreb M, Höfle A, Koenig P, Sommer MS, Sinning I, Wang F, Tews I, Schnell DJ, Schleiff E. 2011. Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33. Biochem J. 436:313-9. [PubMed]

Inoue H, Rounds C, Schnell DJ. 2010. The Molecular Basis for Distinct Pathways for Protein Import into Arabidopsis Chloroplasts.  Plant Cell 22:1947-60. [PubMed]

Viana AB, Li M, Schnell DJ. 2010. Determinants for stop-transfer and post-import pathways for protein targeting to the chloroplast inner envelope membrane. J Biol Chem. 285:12948-60. [PubMed]

Lee J, Wang F, Schnell DJ. 2009. Toc receptor dimerization participates in the initiation of membrane translocation during protein import into chloroplasts. J Biol Chem. 284:31130-41. [PubMed]

Kessler F, Schnell D. 2009. Chloroplast biogenesis: diversity and regulation of the protein import apparatus. Curr Opin Cell Biol. 21:494-500. [PubMed]

Agne B, Infanger S, Wang F, Hofstetter V, Rahim G, Martin M, Lee DW, Hwang I, Schnell D, Kessler F. 2009. A toc159 import receptor mutant, defective in hydrolysis of GTP, supports preprotein import into chloroplasts. J Biol Chem. 284:8670-9. [PubMed]

Han S, Green L, Schnell DJ. 2009. The signal peptide peptidase is required for pollen function in Arabidopsis. Plant Physiol. 149:1289-301. [PubMed]

Singh ND, Li M, Lee SB, Schnell D, Daniell H. 2008. Arabidopsis Tic40 expression in tobacco chloroplasts results in massive proliferation of the inner envelope membrane and upregulation of associated proteins. Plant Cell. 20:3405-17. [PubMed]

Wang F, Agne B, Kessler F, Schnell DJ. 2008. The role of GTP binding and hydrolysis at the atToc159 preprotein receptor during protein import into chloroplasts. J Cell Biol. 183:87-99. [PubMed]

Inaba T. and D. J. Schnell. 2008. Protein trafficking to plastids: one theme, many variations. Biochem J, 413:15-28. [PubMed]

Rounds C., Wang F. and D.J. Schnell. 2007. The Toc machinery of the protein import apparatus of chloroplasts. In The Enzymes. Molecular machines involved in protein transport across membranes, vol XV. RE Dalbey CM Kohler and F Tamanoi, eds.

Li M. and DJ Schnell. 2006. Reconstitution of protein targeting to the inner envelope membrane of chloroplasts. J. Cell Biol. 175: 249-259. [PubMed]