Structural Studies of the Outer Membrane Protein Ail from Y. Pestis

Abstract

The three Yersinia species that are pathogenic for humans each cause distinctive diseases, ranging from gastroenteritis (Y. pseudotuberculosis, Y. enterocolitica) to plague (Y. pestis), one of the most deadly human infectious diseases, classified as a Category A Biothreat Agent. In all three, host recognition and resistance to the complement system are associated with the bacterial outer membrane protein Ail (Attachment invasion locus) and its interactions with the human host proteins Fn (Fibronectin) and Vn (Vitronectin), which play important functions in adhesion, and C4BP (complement component 4b binding protein), which plays important functions in 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 because it is the only one for which the three-dimensional structure, a transmembrane eight-stranded β-barrel, has been determined. 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 have completely different amino acid sequences than those of OmpX and are thought to be responsible for function. Here we present NMR results for Ail reconstituted in lipid bilayers and lipid micelles as well as binding assays aimed at characterizing the interactions of ail with its human host partners.