Structure of a peptidoglycan amidase effector targeted to Gram-negative bacteria by the type VI secretion system.
Chou, S., Bui, N.K., Russell, A.B., Lexa, K.W., Gardiner, T.E., LeRoux, M., Vollmer, W., Mougous, J.D.(2012) Cell Rep 1: 656-664
- PubMed: 22813741 
- DOI: https://doi.org/10.1016/j.celrep.2012.05.016
- Primary Citation of Related Structures:  
4EOB, 4F4M - PubMed Abstract: 
The target range of a bacterial secretion system can be defined by effector substrate specificity or by the efficacy of effector delivery. Here, we report the crystal structure of Tse1, a type VI secretion (T6S) bacteriolytic amidase effector from Pseudomonas aeruginosa. Consistent with its role as a toxin, Tse1 has a more accessible active site than related housekeeping enzymes. The activity of Tse1 against isolated peptidoglycan shows its capacity to act broadly against Gram-negative bacteria and even certain Gram-positive species. Studies with intact cells indicate that Gram-positive bacteria can remain vulnerable to Tse1 despite cell wall modifications. However, interbacterial competition studies demonstrate that Tse1-dependent lysis is restricted to Gram-negative targets. We propose that the previously observed specificity for T6S against Gram-negative bacteria is a consequence of high local effector concentration achieved by T6S-dependent targeting to its site of action rather than inherent effector substrate specificity.
Organizational Affiliation: 
Department of Microbiology, University of Washington, Seattle, WA 98195, USA.