Structural features common to intracellularly acting toxins from bacteria

This mini-review focuses on structural features shared by bacterial intracellularly-acting toxins. These complex proteins adopt an AnBm assembly. Bm is a cellular-uptake machinery that delivers the enzymatic An component, where it specifically modifies an intracellular eukaryotic cell target. In this nomenclature, the m index reflects the mono- or oligomeric (homo or hetero) state of the B component and the n index indicates the number of A molecules that concomitantly bind to Bm. A structural analysis of the available 3D structures suggests that each of the A molecules that constitute the An component can be divided into Alink and Aenz sub-domains, with Alink specifically linking the enzymatically active Aenz domain to a given Bm. This module-based AnBm assembly seems decisive for natural intracellularly-acting toxins to be potent and for the success of engineered toxins.