Fretting about Outer Membrane Protein Biogenesis. How Exactly do they Fold?

Abstract

β-barrel outer-membrane proteins (OMPs) form a large class of proteins which have a diverse range of functions in the outer membrane of Gram-negative bacteria. They often act as molecular gatekeepers controlling cell-to-cell interactions and the movement of substances into and out of the bacterium. The β-barrel assembly machine (BAM), a multi-component protein complex, plays a major role in inserting OMPs into the outer-membrane. Being essential and ubiquitous, the BAM complex is an attractive target for novel antibiotics, but many questions regarding its interactions remain unresolved. We will investigate how the BAM complex facilitates the folding of OMPs at a structural and mechanistic level. To monitor the folding of model E. coli OMPs into lipid bilayers we are developing a fluorescence-based assay. This assay will allow the kinetics of folding of OMPs to be accurately measured in the presence and absence of the BAM complex. Distance measurements between BAM subunits and model OMPs, and within OMPs themselves, will be used to gain information about the sites of interaction between BAM and its substrates, and the mechanism and kinetics of β-barrel folding. Together, these experiments will help guide further studies into the mechanisms of assisted and unassisted folding of OMPs.