Mecky Pohlschröder
Associate Professor, Dept of Biology

Microbiology, Virology and Parasitology Program

Address

201 Leidy Labs
415 University Avenue
Philadelphia, PA 19104-6018

Office tel.: 215 573-2283
Lab tel.: 215 573-2278
Fax: 215 898-8780
E-mail: pohlschr@sas.upenn.edu

Link(s)

Signal Find Server

Dr. Pohlschroder's Dept of Biology Page

Twin Arginine Translocation

Predicted Tat Substrate ... of Prokaryotes

Education

University of Muenster, Germany: Vordiplom (Biology), 1989.

University of Massachusetts, Amherst: PhD (Microbiology), 1994.

Harvard University: Postdoctoral Research (Microbiology), 1994-1998.

Research Interests

• Protein translocation into and across hydrophobic membranes.

Key words: Sec translocation, Twin arginine translocation, membrane protein insertion, cell-surface structures, novel antibiotic targets.

Search PubMed for articles

Description of Research

All organisms are required to translocate a subset of cytoplasmically synthesized proteins into or across hydrophobic membranes. These proteins play a wide variety of invaluable roles in maintaining cell viability, including acquisition of metabolic precursors; secretion of toxins; transduction of signals to the cytoplasm; and formation of extracytoplasmic structures, such as pili and flagella.

Organisms have evolved a number of distinct mechanisms to facilitate this transport, including the Sec system, which transports proteins in an unfolded conformation and is thought to be the major translocation pathway in most organisms, and the twin-arginine translocation (Tat) system, which transports pre-folded proteins. Both pathways exist in bacteria and eukaryotes, and have now been described in archaea.

Our research focuses on both, the Sec and Tat transport mechanisms in Archaea. By studying these processes in organisms of this domain of life, which shares characteristics with bacteria and eukaryotes, we hope to i) define general principles involved in each type of transport; ii) understand the reasons underlying the preferential transport of specific proteins via the Sec vs. Tat pathways; and iii) determine how each process has evolved in the archaea.

We use Haloferax volcanii, which is amenable to genetic and biochemical techniques, as the model organism. Studying H. volcanii, an archaeon that thrives in salt conditions approaching saturation, not only allows us to address the three objectives mentioned above, but also may reveal specific modifications in either secretory pathway that result from adaptation to the high salt conditions they inhabit. These analyses are complemented by in silico studies of translocation pathway components and their translocated substrates.

The haloarchaeal Sec-pathway
Most proteins pass through the endoplasmic reticular membrane of eukaryotes and the cytoplasmic membrane of bacteria via a proteinaceous pore, the Sec-translocon. While the core components of the pore are evolutionarily conserved, many Sec-components are distinct in bacteria and eukaryotes and the functions of most of these proteins are not well understood. Interestingly, archaea contain a combination of bacterial and eukaryotic Sec component homologs. Moreover, it is curious that no archaeal homolog of a known translocation ATPase has been identified. Using a combination of genetic and biochemical approaches we are characterizing H. volcanii homologs of known Sec components and are attempting to identify as yet unknown Sec-components, such as an archaeal translocation ATPase.

The haloarchaeal Tat pathway
Many archaeal species possess unique adaptations that allow for their survival in extreme environments. In the haloarchaea, in silico and in vivo evidence from our laboratory suggests that, while the Sec pathway is crucial for haloarchaeal growth, one such adaptation is the routing of most secreted proteins to the Tat pathway, http://www.sas.upenn.edu/~pohlschr/. This unique characteristic makes studying the haloarchaeal Tat pathway particularly useful, as it provides a wide range of substrates that can be used as reporters to characterize known Tat components as well as for screens and selections to identify putative additional Tat components. Moreover, revealing the significance of haloarchaea-specific Tat-pathway characteristics and comparing such characteristics to non-haloarchaeal systems will reveal information concerning the efficient use of the pathway and lead to a better understanding of the pathway in general. Crucial questions such as “what are the dynamics of pore assembly?”, “how are proteins of drastically different sizes translocated while maintaining the essential semipermeability of the membrane?” and “what are the selective pressures that target substrates to the Tat or Sec pathway?” are still largely elusive.

Finally, it should be noted that eukaryotic homologs of Tat components have only been identified in chloroplasts. Considering the fact that Tat mutants in pathogenic Escherichia coli and Pseudomonas aeroginosa, among others, have been shown to be attenuated for virulence in an animal model, components of this pathway may prove to be attractive drug targets (http://www.sas.upenn.edu/~pohlschr/tatprok.html).

Recent Publications

Widdick, D., K. Dilks, G. Chandra, A. Bottrill, M. Naldrett, M. Pohlschröder and Tracy Palmer. Secretome analysis reveals that the twin-agrinine translocation (Tat) pathway is a major route of protein export in Streptomyces coelicolor. PNAS, in press

Hand, N. J., A. Laskewitz, R. Klein, and M. Pohlschröder. 2006. Archaeal and bacterial SecD and SecF homologs exhibit striking structural and functional conservation. J. Bacteriol. 188. 1251-1259.

Dilks, K. M. I. Gimenez, and M. Pohlschröder. 2005. Genetic and biochemical analysis of the twin-arginine translocation pathway in halophilic archaea. J. Bacteriol. 187: 8104-8113.

Haddad, A., R. W. Rose, M. Pohlschröder. 2005. The Haloferax volcanii FtsY homolog is critical for haloarcheal growth but does not require the A-domain. J. Bacteriol. 187:4015-4022.

Pohlschröder, M., E. Hartmann, M, N. J. Hand, K. Dilks, M. A. Haddad. 2005. Diversity and evolution of protein translocation. Annual Reviews in Microbiology. 59:91-111.

Lab

Rotation Projects for 2006-2007

1. In vivo characterization of H. volcanii homologs of known Sec or Tat components
2. Genetic screens and selections, as well as co-purification approaches to identify translocation components. These may include additional archaea-specific components, or components that have not yet been identified in bacteria or eukaryotes.
3. Characterization of Tat and Sec substrates to elucidate the evolutionary pressures that directs a given target to a particular translocation pathway.

Lab personnel:

Maria Ines Gimenes, Postdoctoral Fellow
Stefanie Storf, Postdoctoral Fellow
Kai-Fen Chang, Graduate Student
Steve, Yi-Fu Yen, Graduate Student
Yen-Fu Lee, Undergraduate Student