Hijacking pathogenic membrane proteins to engineer cellular entry: A molecular biophysics approach
Invasive pathogenic bacteria feature many cellular niches and life cycles, for which they have developed functions that are potentially attractive in biotechnology and therapeutic delivery applications. One such function is tissue-specific bacterial engulfment in human cells which do not normally undergo phagocytosis. Opacity-associated (Opa) proteins of Neisseria gonorrhoeae and N. meningitides are eight-stranded outer membrane proteins that bind to different host receptors, triggering engulfment of the bacterium. Receptor selectivity is determined by regions of the extracellular loops with high sequence variability; to date, 338 distinct opa alleles have been sequenced. Our hybrid NMR and molecular dynamics structure of an Opa reveals that the variable regions are dynamic and disordered, and sample conformations that may be competent for receptor binding. To complement our structural studies, Opa – human receptor interactions are being examined in vitro and in vivo, using liposomes and nanodiscs. In vitro studies focus on the strength and specificity of the interaction, while our in vivo studies are elucidating the cell fate and signaling of Opa liposomes. Our work suggests that a high degree of structural plasticity is required to tolerate the diverse sequences, and the dynamic ensemble allows sampling of conformers competent to engage receptors. Thus, perhaps counterintuitively, conformational plasticity offers a mechanism for functional versatility in this remarkable biological system
Despite significant progress in the area of membrane protein structure and stability, many questions still remain. One fundamental question is what is the role of the lipid environment in stabilizing membrane protein structure, function, and dynamics. To begin to understand the interactions between proteins and the solvent environment, the physical properties of the environments used to stabilize membrane protein folds need to be understood. The structure, shape, and dynamics of micelles, bicelles, and membranes will be presented and compared. The impact the differences and similarities of these three environments have on membrane protein structure will be explored.