Search

Yersinia pestis enters host cells and evades host defenses, in part, through interactions between Yersinia pestis proteins and host membranes. One such interaction is through the type III secretion system, which uses a highly conserved and ordered complex for Yersinia pestis outer membrane effector protein translocation called the injectisome. The portion of the injectisome that interacts directly with host cell membranes is referred to as the translocon. The translocon is believed to form a pore allowing effector molecules to enter host cells. To facilitate mechanistic studies of the translocon, we have developed a cell-free approach for expressing translocon pore proteins as a complex supported in a bilayer membrane mimetic nano-scaffold known as a nanolipoprotein particle (NLP) Initial results show cell-free expression of Yersinia pestis outer membrane proteins YopB and YopD was enhanced in the presence of liposomes. However, these complexes tended to aggregate and precipitate. With the addition of co-expressed (NLP) forming components, the YopB and/or YopD complex was rendered soluble, increasing the yield of protein for biophysical studies. Biophysical methods such as Atomic Force Microscopy and Fluorescence Correlation Spectroscopy were used to confirm that the soluble YopB/D complex was associated with NLPs. An interaction between the YopB/D complex and NLP was validated by immunoprecipitation. The YopB/D translocon complex embedded in a NLP provides a platform for protein interaction studies between pathogen and host proteins. These studies will help elucidate the poorly understood mechanism which enables this pathogen to inject effector proteins into host cells, thus evading host defenses.

The formation of different sized nanoliprotein particles (NLPs) by the interactions between apolipoproteins and phospholipids is discussed. The selection of apolipoprotein used in an assembly causes the size and homogenity of the final nanostructure.

Membrane-associated proteins and protein complexes account for approximately a third or more of the proteins in the cell (1, 2). These complexes mediate essential cellular processes; including signal transduc-tion, transport, recognition, bioenergetics and cell-cell communication. In general, membrane proteins are challenging to study because of their insolubility and tendency to aggregate when removed from their protein lipid bilayer environment. This chapter is focused on describing a novel method for producing and solubilizing membrane proteins that can be easily adapted to high-throughput expression screening. This process is based on cell-free transcription and translation technology coupled with nanolipoprotein par ticles (NLPs), which are lipid bilayers confined within a ring of amphipathic protein of defined diameter. The NLPs act as a platform for inserting, solubilizing and characterizing functional membrane proteins. NLP component proteins (apolipoproteins), as well as membrane proteins can be produced by either traditional cell-based or as discussed here, cell-free expression methodologies.