Navigation Links
Critical step traced in anthrax infection

Scientists at Harvard Medical School (HMS) have revealed details of a key step in the entry of anthrax toxin into human cells. The work, which grew out of an ongoing effort to produce a better anthrax therapeutic, shows that the protective antigen component of the bacterial toxin plays an active role in transferring the other two components of the toxin through the cell membrane.

The research, led by R. John Collier, professor of microbiology and molecular genetics at HMS, provides insight into the broader question of how proteins cross cell membranes. The findings appear in the July 29 issue of Science.

An anthrax bacterium secretes three nontoxic proteins that assemble into a toxic complex on the surface of the host cell to set off a chain of events leading to cell toxicity and death. Protective antigen (PA) is one of these proteins, and after binding to the cell, seven copies of it assemble into a specific complex that is capable of forming a pore in a cellular membrane. The pore permits the other two proteins, lethal factor (LF) and edema factor (EF), to enter the cell interior, where the factors interfere with metabolic processes, leading to death of the infected individual.

Details surrounding this process are continuing to be uncovered in Collier's lab. "Until now, we have not known whether the PA pore serves simply as a passive conduit, or alternatively, plays an active role in shepherding the unfolded LF and EF molecules through," he said. The findings show that it is the latter?the pore takes an active role in protein translocation.

The scientists demonstrated this role by investigating the channel's chemical make-up. Using a procedure known as cysteine-scanning mutagenesis, they identified the hydrophobic, or "greasy," amino acid phenylalanine in protective antigen's pore-forming domain. Seven of these amino acids project into the lumen of the pore and form a collection of greasy residues, nicknamed "the phi-clamp" by the sc ientists. Because the water-filled lumen of the membrane pore is smaller than the folded lethal factor and edema factor, these proteins must first unfold before being actively translocated through the heptameric channel. The clamp appears to work as a chaperone, interacting with the hydrophobic sequences on the two factors as they unfold during translocation. The researchers demonstrated that the phi-clamp was critical to infection by mutating the region and thereby blocking translocation of the toxin proteins.

These recent experimental results extend and explain a 1999 discovery by the Collier lab identifying a set of mutations in protective antigen that prevent translocation, some of which represented a new type of antitoxin that may be useful in anthrax treatment.

In the recent work, Collier and his colleagues found that the phi-clamp composes the main conductance-blocking site for hydrophobic drugs, and it is one of their targets for further investigation. "I believe discovery of the phi-clamp will prove to be one of the high points along the path to understanding how translocation occurs in this system," Collier said.

One of the greatest strengths of the experiment, according to Collier, was the integrative use of technologies applied to the testing procedures. Both cellular systems and model electrophysiological membrane systems were used to test the potency of the anthrax toxin. "We tried to bridge reductionist science with the in vivo situation ?we have to do both to make correlations," he said.

The researchers, who were funded by the National Institutes of Health and the National Science Foundation, will continue to study protein unfolding in translocation during anthrax infection, which may prove to be relevant in other biological systems. "This is only a partial picture," Collier said. "There are still major outstanding questions about the overall process that need to be addressed."


'"/>

Source:Harvard Medical School


Related biology news :

1. Critical role in programmed cell death identified
2. White Blood Cell Waste Disposal System Plays Critical Regulatory Role
3. Critical hearing gene helps send auditory messages to brain
4. Scientists seek answers on what activates deadly anthrax spores
5. Antibodies from plants protect against anthrax
6. Defensins neutralize anthrax toxin
7. US Army plans to bulk-buy anthrax
8. New antibody shows promise as cure for anthrax
9. Effective, safe anthrax vaccine can be grown in tobacco plants
10. UCSD study finds anthrax toxins also harmful to fruit flies
11. Driver of anthrax toxicity could lead to late-stage therapy
Post Your Comments:
*Name:
*Comment:
*Email:


(Date:4/28/2016)... First quarter 2016:   , Revenues amounted ... quarter of 2015 The gross margin was 49% (27) ... the operating margin was 40% (-13) Earnings per share ... operations was SEK 249.9 M (21.2) , Outlook   ... M. The operating margin for 2016 is estimated to ...
(Date:4/15/2016)... -- Research and Markets has announced the ...  report to their offering.  ,      ... gait biometrics market is expected to grow at ... Gait analysis generates multiple variables such ... compute factors that are not or cannot be ...
(Date:3/29/2016)... 2016 LegacyXChange, Inc. (OTC: ... SelectaDNA/CSI Protect are pleased to announce our successful effort ... variety of writing instruments, ensuring athletes signatures against counterfeiting ... from athletes on LegacyXChange will be assured of ongoing ... Bill Bollander , CEO states, "By ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... 23, 2016 Apellis Pharmaceuticals, Inc. today ... trials of its complement C3 inhibitor, APL-2. The ... ascending dose studies designed to assess the safety, ... injection in healthy adult volunteers. Forty ... a single dose (ranging from 45 to 1,440mg) ...
(Date:6/23/2016)... ... June 23, 2016 , ... Regulatory Compliance Associates® Inc. (RCA), ... free webinar on Performing Quality Investigations: Getting to Root Cause. ... no charge. , Incomplete investigations are still a major concern to the Regulatory ...
(Date:6/22/2016)... 2016 Research and Markets has announced the ... to their offering. The ... $29.3 billion in 2013. The market is expected to grow at ... to 2020, increasing from $50.6 billion in 2015 to $96.6 billion ... the forecast period (2015 to 2020) are discussed. As well, new ...
(Date:6/22/2016)... ... June 21, 2016 , ... New light-based technologies that facilitate a “look inside” ... to enable both compact, wearable devices for point-of-care diagnostics as well as powerful new ... Recent work and visionary future directions are detailed in a new open-access article by ...
Breaking Biology Technology: