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Abstract

Intimin and Invasin are well-characterised virulence factors of enterophathogenic Escherichia coli and yersiniae, respectively. These outer membrane proteins belong to a family of proteins whose extracellular domain is secreted through the outer membrane by a novel autotransport mechanism, termed type Ve secretion [1]. Compared to classical (type Va) autotransporters, Intimin and Invasin have an inverted topology, with the C-terminal passenger being exported through an N- terminal -barrel pore [2]. In addition, these proteins have an N-terminal periplasmic domain with homology to LysM. We show that the periplasmic domain of Intimin, but not the corresponding, smaller domain of Invasin, binds to peptidoglycan, and that Ca 2+ ions enhance this binding. Furthermore, the Intimin periplasmic domain mediates dimerisation. The C-terminal passenger domains of Invasin and Intimin contains an array of repeated immunoglobulin (Ig)-like domains [3,4]. We have identified a further Ig domain at the N-terminus of the passenger, which may be involved in passenger export. In addition, we have produced and refolded the -barrel translocator domain of Invasin for crystallisation trials. The structure of this domain would confirm our topology model and offer insight into this new mechanism of autotransport.