Chapter 6 - Toxin receptors

Abstract

This chapter deals with bacterial toxin receptors, which play pivotal roles in host cell function, as well as intoxication by bacterial toxins. Although the molecular nature of the receptors varies depending on the toxins involved, they all bind the toxins, then either transduce particular signals into the cell cytoplasm or are involved in the internalization of the toxins. For a cellular substance to be accepted as a bacterial toxin receptor, two criteria must be at least satisfied. First, it must be demonstrated that the substance has a property of binding directly and specifically to the toxin. The second criteria addresses cell sensitivity to the toxin. This must depend on the expression level of the substance. Critical methods involved in receptor identification are reviewed. The use of expression cloning techniques would provide the most powerful way to identify toxin receptors and their cDNA cloning. In this case, a cDNA library produced by transcripts from toxin-susceptible cells is generally transfected to toxin-resistant recipient cells and cells that become toxinsensitive are picked up. Identification and molecular characterization of their receptors are not only essential to understanding the intoxication mechanism of bacterial toxins, but also valuable for analyzing native functions of host cell proteins. Membrane proteins that are ubiquitously present and essential for host cell membrane would be favorable for bacteria to exert their toxic actions to a large extent, and thus such membrane proteins must be particularly selected as toxin receptors. Recent progress on analytical methods for dealing with small protein amounts seems to have eased the identification of toxin receptors.