Research into the mechanisms of protein transport in bacteria may provide glimpses into the evolution of the organisms and aid future drug development, University of Pennsylvania professor Mecky Pohlschröder said as she explained her research at Dartmouth Medical School’s microbiology and immunology seminar last Monday.

Protein translocation plays a significant role in cellular function, cell defense, digestion, communication and transport. Organisms have developed various systems for protein transport across hydrophobic membranes. Pohlschröder studies two protein transport mechanisms in Archaea: the Sec and Tat pathways.

The Sec pathway is common in bacteria as well as eukaryotes. Proteins pass through the membranes of the endoplasmic reticulum into the cytoplasm by means of a pore called the Sec-translocon, according to Pohlschröder’s web site. These pores are distinct in eukaryotes and prokaryotes and require greater understanding. In Archaea, this pathway seems to be a combination of those found in prokaryotes and eukaryotes.

However, Pohlschröder said, “[Archaea] lack a homologue of the bacterial and eukaryotic translocation ATPases.”

In the Sec pathway, proteins are unfolded when transported and then folded again after they have been translocated across the lipid bi-layer.

The Tat pathway, also called the twin arginine translocation pathway, is commonly observed in prokaryotes and chloroplasts. Pohlschröder’s research focuses on Haloferax volcanii, a halophilic Archaea that thrives in extremely high-salt concentrations. Unlike non-haloarchaea that use the Tat pathway only for certain proteins, H. volcanii uses it to transport the majority of its proteins. This may be an adaptation to the high-salt environment in which this organism thrives.

The Tat pathway is based on three components: Tar C, Tat B and Tat C. Tat C and Tat B are necessary to recognize the substrate and transmit the necessary information to Tat A, which then allows the transmission of the protein. Tat C can join to another Tat C molecule to form a complex that allows faster translocation of proteins across the membrane.

Pohlschröder explained that her research is required to understand the mechanisms of protein transport, their relative advantages and disadvantages as well as the evolution of these two systems. Further understanding of these systems would greatly benefit drug development by identifying drug targets in protein pathways, she said.