Identification of Burkholderia lethal factor 1

Claire Williams, University of Cambridge School of Clinical Medicine, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0SP

Burkholderia pseudomallei is a Gram negative bacteria which is endemic in South East Asia and is the causative agent of melioidosis. Humans become infected when they come into contact with environmental sources of the bacteria, typically in moist soil and stagnant water such as found in rice paddies. Melioidosis can present in various non-specific ways, ranging from a chronic local infection to an acute septicaemia. The bacteria can remain latent in the body for decades, no vaccine is available, treatment is complicated due to multidrug resistance, and the organism is on a list of those which may potentially be used in bioterrorism. The molecular mechanisms underlying the disease caused by B. pseudomallei aren’t well understood. In an attempt to increase our knowledge in this area, the structures of bacterial proteins of unknown function are being studied. A study looking at one such protein- BPSL1549, is presented in this week’s edition of Science (1).

Once the structure of BPSL1549 was elucidated it became apparent that it shares remarkable structural similarity to the E. coli protein cytotoxic necrotizing factor 1 (CNF1-C). This protein inactivates Rho GTPases via deamidation of glutamine, altering the actin cytoskeleton and resulting in cell death. Despite a structural similarity, there is virtually no sequence similarity between BPSL1549 and CNF1-C. One motif which is present in both proteins is a 4 amino acid stretch known to be crucial for deamidase activity, suggesting that BPSL1549 may also have this function and therefore be cytotoxic. Indeed intraperitoneal injection of the protein into mice results in death within 14 days. An engineered version of the protein with a point mutation in the domain responsible for deamidation is non-toxic, highlighting the importance of this activity to the virulence of B. pseudomallei.

To determine how BPSL1549 causes cytotoxicity, the cellular proteins it binds to were identified using co-immunoprecipitations. The major protein identified was the helicase eIF4A, suggesting that the bacterial protein is interfering with translation initiation. Indeed further experiments revealed that BPSL1549 results in the deamidation of a glutamine to glutamate, inhibiting the helicase activity of eIF4A and stalling the initiation of translation causing cell death. As a result of these findings, the authors suggest that BPSL1549 be renamed Burkholderia lethal factor 1.

References: 

1. Cruz-Migoni A, Hautbergue GM, Artymiuk PJ, Baker PJ, Bokori-Brown M, Chang C-T, Dickman MJ, Essex-Lopresti A, Harding SV, Mahadi NM, Marshall LE, Mobbs GW, Mohamed R, Nathan S, Ngugi SA, Ong C, Ooi WF, Partridge LJ, Phillips HL, Raih MF, Ruzheinikov S, Sarkar-Tyson M, Sedelnikova SE, Smither SJ, Tan P, Titball RW, Wilson SA, Rice DW. A Burkholderia pseudomallei Toxin Inhibits Helicase Activity of Translation Factor eIF4A. Science 2011 Nov;334(6057):821 -824.
doi: 10.1126/science.1211915

Story image from Wikimedia Commons.