Host Receptors of Bacterial Origin

This chapter illustrates how specific pathogenic bacteria participate in a sophisticated cross talk with their host by highlighting recent advances in the understanding of the structure and function of the first identified host receptor of bacterial origin—the translocated intimin receptor (Tir) from enteropathogenic Escherichia coli (EPEC) and its cognate adhesin intimin. EPEC, an extracellular bacterial pathogen which infects humans by colonizing the intestinal mucosa, is a major cause of infantile diarrhea in developing countries and continues to be a major health threat worldwide. The locus of enterocyte effacement (LEE)5/Tir operon contains three important genes directly involved in the intimate attachment of bacteria to host: eae, which encodes the outer membrane adhesion molecule known as intimin; tir, which encodes the translocated intimin receptor (Tir); and cesT, which encodes the type III chaperone of Tir. Recent structural and biochemical studies have provided further insights into the molecular details of the Tir-intimin interaction with respect to intimate attachment; and this chapter reviews some of these aspects. Since the discovery of EPEC Tir, bacterially derived receptors have been identified only in the attaching and effacing (A/E) family of pathogens, and all of them are Tir orthologues. It is still puzzling why similar types of receptors have not been identified in other bacterial pathogens. The chapter speculates that a number of reasons contribute to the difficulty in identifying other receptors of bacterial origin.