SummaryThe spirochaetal agents of Lyme disease, Borrelia burgdorferi (sensu lato) bind to integrins ␣ IIb ␤ 3 , ␣ v ␤ 3 and ␣ 5 ␤ 1 in purified form and on the surfaces of human cells. Using a phage display library of B. burgdorferi (sensu stricto) DNA, a candidate ligand for ␤ 3 -chain integrins was identified. The native B. burgdorferi protein, termed p66, is known to be recognized by human Lyme disease patient sera and to be expressed on the surface of the spirochaete. We show here that recombinant p66 binds specifically to ␤ 3 -chain integrins and inhibits attachment of intact B. burgdorferi to the same integrins. When expressed on the surface of Escherichia coli, this protein increases the attachment of E. coli to a transfected cell line that expresses ␣ v ␤ 3 , but not to the parental cell line, which expresses no ␤ 3 -chain integrins. Localization of p66 on the surface of B. burgdorferi, the ability of recombinant forms of the protein to bind to ␤ 3 -chain integrins and the fact that p66 and B. burgdorferi bind to ␤ 3 -chain integrins in a mutually exclusive manner make p66 an attractive candidate bacterial ligand for integrins ␣ IIb ␤ 3 and ␣ v ␤ 3 .

Host cell binding is an essential step in colonization by many bacterial pathogens, and the Lyme disease agent, Borrelia burgdorferi, which colonizes multiple tissues, is capable of attachment to diverse cell types. Glycosaminoglycans (GAGs) are ubiquitously expressed on mammalian cells and are recognized by multiple B. burgdorferi surface proteins. We previously showed that B. burgdorferi strains differ in the particular spectrum of GAGs that they recognize, leading to differences in the cultured mammalian cell types that they efficiently bind. The molecular basis of these binding specificities remains undefined, due to the difficulty of analyzing multiple, potentially redundant cell attachment pathways and to the paucity of genetic tools for this pathogen. In the current study, we show that the expression of decorin-binding protein (

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). To study mac variation and expression of the Mac protein, the gene in 67 GAS strains representing 36 distinct M protein serotypes was sequenced. Two distinct genetic complexes were identified, and they were designated complex I and complex II. Mac variants in each of the two complexes were closely related, but complex I and complex II variants differed on average at 50.66 ؎ 5.8 amino acid residues, most of which were located in the middle one-third of the protein. Taken together, the data add to the emerging theme in GAS pathogenesis that allelic variation in virulence genes contributes to fundamental differences in host-pathogen interactions among strains.

Enterohaemorrhagic Escherichia coli (EHEC) has emerged as an important agent of diarrhoeal disease. Attachment to host cells, an essential step during intestinal colonization by EHEC, is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (A/E) lesion, directly beneath bound bacteria. The outer membrane protein intimin is required for the formation of this structure, as is Tir, a bacterial protein that is translocated into the host cell and is thought to function as a receptor for intimin. To understand intimin function better, we fused EHEC intimin to a homologous protein, Yersinia pseudotuberculosis invasin, or to maltose-binding protein. The N-terminal 539 amino acids of intimin were sufficient to promote outer membrane localization of the C-terminus of invasin and, conversely, the N-terminal 489 amino acids of invasin were sufficient to promote the localization of the C-terminus of intimin. The C-terminal 181 residues of intimin were sufficient to bind mammalian cells that had been preinfected with an enteropathogenic E. coli strain that expresses Tir but not intimin. Binding of intimin derivatives to preinfected cells correlated with binding to recombinant Tir protein. Finally, the 181-residue minimal Tir-binding region of intimin, when purified and immobilized on latex beads, was sufficient to trigger A/E lesions on preinfected mammalian cells