The activity of a bacterial effector protein seen in molecular detail
Many plant and animal pathogens deploy effector proteins as part of their ‘molecular arsenal’ to facilitate infection and colonisation of their hosts. New research has revealed the structure of a bacterial effector molecule bound to its target protein in the host.
Gram-negative bacterial pathogens can deliver effector proteins through a specific secretion system, directly into host cells, to manipulate host cell processes for the benefit of the pathogen. The host cell processes targeted by effectors and the mechanisms used for manipulation are diverse. Knowledge of how effectors interface with host cell molecules is critical for understanding both mechanisms of pathogenesis and how effectors could be used to deliver new insights into host cell biology.
Dr Mark Banfield at the John Innes Centre, funded by a grant from the Biotechnology and Biological Sciences Research Council (BBSRC), has uncovered the structure of a bacterial effector molecule called ‘Cif’ bound to its target (NEDD8) from the host. The Cif effector is found in a number of pathogenic bacteria including strains of E. coli, Burkholderia, Photorhabdus and Yersinia species.
Delivery of Cif into host cells results in perturbation of the cell division cycle. One hypothesis suggests this could prevent rapid renewal of infected cells, such as those in the lining of the gut, so helping bacterial colonisation. Researchers at the John Innes Centre also studied the enzymatic activity of the effector protein in solution, and in collaboration with Drs. Taieb and Oswald, who are based in Toulouse, France, in model host cells.
Their work, published in the Proceedings of the National Academy of Sciences Online Early Edition, used protein structure determination to reveal the interface formed between the bacterial effector and the host target. The knowledge of this interface at the molecular level allowed small, directed changes to be made to the effector to determine the regions of the interface important for the interaction and the enzymatic activity in solution and in cells.
Putative catalytic mechanism for Cif based on available structural data. Cif (carbon atoms shown in green) converts a glutamine residue of NEDD8 (carbon atoms shown in cyan) into a glutamate, a deamidation reaction. The reaction proceeds via an enzyme-substrate thioester intermediate (formed between a cysteine residue of Cif and the NEDD8 glutamine, with the loss of ammonia (blue sphere)). This intermediate is then hydrolysed by a water molecule (red sphere)
A thorough understanding of how this effector acts at the molecular level not only provides new information about the virulence mechanisms used by pathogens, it also suggests ways in which these effectors could be used as tools to probe functions related to the cell cycle, and how this relates to cellular biology.
Reference: The molecular basis of ubiquitin-like protein NEDD8 deamidation by the bacterial effector protein Cif, Allister Crow, Richard K. Hughes, Frédéric Taieb, Eric Oswald & Mark J. Banfield, PNAS 109 (27) E1830-E1838 doi: 10.1073/pnas.1112107109
About the John Innes Centre:
The John Innes Centre, www.jic.ac.uk, is a world-leading research centre based on the Norwich Research Park www.nrp.org.uk. The JIC’s mission is to generate knowledge of plants and microbes through innovative research, to train scientists for the future, and to apply its knowledge to benefit agriculture, human health and well-being, and the environment. JIC delivers world class bioscience outcomes leading to wealth and job creation, and generating high returns for the UK economy. JIC is one of eight institutes that receive strategic funding from the Biotechnology and Biological Sciences Research Council and received a total of £28.4M investment in 2010-11.