Dr. Danny J. Schnell
Professor, Biochemistry and Molecular Biology
 University of Massachusetts at Amherst
dschnell@biochem.umass.edu

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

Background and Training

Ph.D.: Dept. Biochemistry and Biophysics, University of California
Postdoctoral training: Laboratory of Cell Biology, 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.
Representative Publications

1. Huang J, Taylor JP, Chen JG, Uhrig JF, Schnell DJ, Nakagawa T, Korth KL, Jones AM. 2006. The Plastid Protein THYLAKOID FORMATION1 and the Plasma Membrane G-Protein GPA1 Interact in a Novel Sugar-Signaling Mechanism in Arabidopsis. Plant Cell. Mar 31; [Epub ahead of print]

2. Kessler F, Schnell DJ. 2006. The function and diversity of plastid protein import pathways: a multilane GTPase highway into plastids. Traffic. Mar;7(3):248-57.

3. Inaba, T., Alvarez-Huerta, M., Li, M., Bauer,B., Ewers, C., Kessler, F. and D.J. Schnell. 2005.  atTic110 is essential for the assembly and function of the protein import machinery of plastids. Plant Cell. 17:1482-96.


4. Smith, M.D. and D.J. Schnell. 2004. Chloroplast protein targeting: multiple pathways for a complex organelle in Protein movement across membranes.  J. Eichler, ed.  Landes Biosciences, Georgetown, TX., pg. 1-18.


5. Tu S.-H., Chen, L.-J., Smith, M.D., Su, Y.S., Schnell, D.J. and H.-M. Li.  2004.  Import pathways of chloroplast interior proteins and outer-membrane proteins converge at Toc75. Plant Cell 16: 2078-2088.


6. Kessler, F. and D.J. Schnell. 2004.  Chloroplast protein import: solve the GTPase riddle for entry!. Trends Cell Biol. 14:334-338.


7. Ivanova, Y., Smith, M.D., Chen, K. and D. J. Schnell. 2004. Members of the Toc159 import receptor family represent distinct pathways for protein import into plastids. Mol. Biol. Cell, 15:3379-3392.


8. Smith, M.D, Rounds, C.M., Wang, F., Chen, K., Afitlhile, M. and D.J. Schnell. 2004.  The cytoplasmic form of atToc159 is a selective transit peptide receptor for the import of nucleus-encoded chloroplast proteins.  J. Cell Biol. 165: 323-334.


9. Wallas, T.R., Smith, M.D., Sanchez-Nieto, S. and D.J. Schnell.  2003.  The roles of Toc34 and Toc75 in targeting the Toc159 preprotein receptor to chloroplasts.  J. Biol. Chem. 278:44289-97.


10. Inaba, T., Li, M., Alvarez-Huerta, M., Kessler, F. and D.J. Schnell. 2003. atTic110 Functions as a Scaffold for Coordinating the Stromal Events of Protein Import into Chloroplasts.  J. Biol. Chem. 278:38617-27.


11. Schnell D.J. and D.N. Hebert. 2003. Protein translocons: multifunctional mediators of protein translocation across membranes. Cell 112:491-505


12. Bauer, J., Hiltbrunner, A., Weibel, P., Vidi, P.A., Alvarez-Huerta, M., Smith, M.D., Schnell, D.J. and F. Kessler. 2002. Essential role of the G-domain in targeting of the protein import receptor atToc159 to the chloroplast outer membrane.  J. Cell Biol. 159: 845-854.


13. Smith, M.D., Hiltbrunner, A., Kessler, F. and D.J. Schnell. 2002. The targeting of the atToc159 preprotein receptor to the chloroplast outer membrane is mediated by its GTPase domain and is regulated by GTP.  J. Cell Biol. 159: 833-843.


14. Kessler, F. and D.J. Schnell.  2002. A GTPase gate for protein import into chloroplasts.  Nat. Struct. Biol. 9:81-83


15. Chen, X., Smith, M.D., Fitzpatrick, L. and D.J. Schnell.  2002.  In vivo analysis of the role of atTic20 in protein import into chloroplasts. Plant Cell 14:641-654


16. Smith, M.D., Fitzpatrick, L., Keegstra, K. and D.J. Schnell.  2002.  In vitro analysis of chloroplast protein import.  In Current Protocols in Cell Biology, J. S. Bonifacino, M. Dasso, J. B. Harford, J. Lippincott-Schwartz, and K.M. Yamada, eds. NY: John Wiley & Sons Inc.


17. Smith, M.D. and D.J. Schnell. 2001. Peroxisomal protein import. the paradigm shifts. Cell 105:293-296.