Type III secretion systems shape up as they ship out

Virulence associated protein type III secretion systems (T3SSs) are intricately structured organic nanosyringes that achieve the translocation of bacterial proteins from the prokaryotic cytoplasm across three membranes into the host cytosol. The substrates for these systems number in the hundreds, with remarkably diverse biological activities, modulating host cell biology for the benefit of the pathogen. Although there has been tremendous progress on the structure and function of the T3SS substrates, there has been comparatively little progress on the much more highly conserved secretion apparatus itself. This review summarizes recent advances in the field of structural microbiology that have begun to address this shortcoming, finally bringing to bear the power of structural biology to this central virulence system of Gram-negative bacterial pathogens.