Scientists from the Institut Pasteur, Inserm and INRA have recently discovered in the pathogenic bacterium Listeria monocytogenes, responsible for listoriosis, a miniprotein also found in many other bacteria, which enables Listeria to survive during infection. This protein is the link that scientists have long been trying to find between occurrence of a stress and the activation of a defense program by the bacterium in response to a sudden change in environment. This discovery was made possible by the use of a new, highly powerful approach known as "N-terminomics". The findings have been published in the journal Nature Microbiology.
Listeria monocytogenes bacteria are responsible for listeriosis, a foodborne infection that can be especially severe for pregnant women and their unborn children and for the elderly. These bacteria are now also recognized as an excellent experimental model for research on the defense strategies pathogens adopt in response to the reactions of the organism they are infecting.
The Bacteria-Cell Interactions Unit (Institut Pasteur, Inserm, INRA), directed by Pascale Cossart, has been investigating Listeria as a model for many years. This week, the scientists published a pioneering study that describes the first application of a new technique, N-terminomics, to Listeria. This technique identifies the sites where protein translation begins and enables scientists to identify all the proteins produced by the bacteria, including small proteins that cannot be easily detected using other methods.
The extreme precision of this approach revealed six miniproteins (proteins with fewer than 50 amino acids) in Listeria, including Prli42, a protein that can also be found in many other bacterial species. The scientists then determined that Prli42 is a membrane mini-protein which interacts in the bacterium with components similar to those present in an important defense complex known to exist in Bacillus bacteria: the stressosome. In the event of an attack, or stress, this protein machinery is capable of triggering a vast program of gene expression that enables the bacteria to protect themselves. After identifying Prli42 and its protein partners, the scientists went on to demonstrate the previously unsuspected existence of a stressosome in Listeria. They achieved this by reconstituting it with purified constituents and viewing it using electron microscopy.
The scientists then went even further, identifying the sites of interaction between Prli42 and the stressosome and describing the precise function of Prli42: it is capable of detecting oxidative stress (H2O2) to which bacteria are submitted for example in the blood or macrophages. This stress activates the stressosome at the membrane, enabling it to trigger the expression of sigma B-dependent genes, already identified as key players in stress-induced defense, and especially virulence genes.
This research using N-terminomics therefore revealed the existence in Listeria of Prli42, a long sought-after transmission mini-protein which activates the stressosome. For the first time, the scientists demonstrated how this major complex, also found in other bacteria, detects stress and triggers an appropriate response which ultimately enables the bacteria to survive during infection.
N-terminomics identifies Prli42, a membrane miniprotein conserved in Firmicutes and critical for stressosome activation in Listeria monocytogenes, Nature Microbiology, January 13, 2017
Francis Impens1,2,3#, Nathalie Rolhion1,2,3#, Lilliana Radoshevich1,2,3#, Christophe Bécavin1,2,3,4, Mélodie Duval1,2,3, Jeffrey Mellin1,2,3, Francisco García del Portillo5, M. Graciela Pucciarelli5,6, Allison H. Williams7,8, Pascale Cossart1,2,3,*
(1) Institut Pasteur, Bacteria-Cell Interactions Unit, Department of Cell Biology and Infection, F-75015 Paris, France.
(2) Inserm, U604, F-75015 Paris, France.
(3) INRA, Unit under contract 2020, F-75015 Paris, France.
(4) Institut Pasteur, Bioinformatics and Biostatistics Hub, C3BI, USR 3756 IP CNRS, Paris, France.
(5) Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CNBCSIC), Madrid, Spain.
(6) Departamento de Biología Molecular, Universidad Autónoma de Madrid, Centro de Biología Molecular ‘Severo Ochoa’ (CBMSO-CSIC), Madrid, Spain.
(7) Institut Pasteur, Biology and Genetics of the Bacterial Cell Wall Unit, Department of Microbiology, F-75015 Paris, France.
(8) Inserm, Avenir Group, F-75015 Paris, France.
# These authors made a similar contribution to this work.