Structural and Functional Studies of the Outer Membrane Protein Ail from Yersinia Pestis

Abstract

Ail (Attachment invasion locus) is a virulence factor outer membrane protein of Yersinia pestis, a devastating human pathogen that causes plague. Ail plays key roles in mediating adhesion and providing resistance to human complement, making it a prime candidate target for drug development. It interacts with several human host proteins, including fibronectin, to regulate adhesion and innate immunity. Ail belongs to the Ail/Lom family (pfam PF06316) of outer membrane proteins, whose members share amino acid sequence homology in the membrane-spanning segments, but vary widely in the sequences of the extracellular loops. E. coli OmpX is regarded as the prototypical member of this family, with transmembrane eight-stranded β-barrel and four extracellular loops. However, while Ail has marked adhesion/invasion activity and is essential for virulence, OmpX has no identified function and is not essential. The four extracellular loops of Ail are thought to be responsible for function. Here we present NMR structural data obtained for Ail in detergent micelles, phospholipid vesicles and phospholipid nanodiscs. Since Ail is an integral membrane protein, understanding the molecular mechanism underpinning its function requires structure determination within the phospholipid bilayer membrane. NMR spectroscopy is unique in its ability to provide high-resolution information in lipid environments that closely resemble the cellular membranes. The NMR results are correlated with functional studies that characterize the interactions of Ail with its human protein partners essential for its function in cell adhesion.