Scientists make leap forwards in efforts to combat antibiotic resistance

UK scientists and technology support breakthrough in the fight against superbugs

View of the LptDE complex from outside of the bacterial cell with LptD shown in rainbow and LptE in grey The lipopolysaccharide (LPS) molecule that acts as a camouflage on the cell exterior enters the protein on the left hand side of the pore from the rear and extends out of the front. Finally LPS enters the outer membrane of the cell through an opening between the red and blue strands of LptD.
View of the LptDE complex from outside of the bacterial cell with LptD shown in rainbow and LptE in grey The lipopolysaccharide (LPS) molecule that acts as a camouflage on the cell exterior enters the protein on the left hand side of the pore from the rear and extends out of the front. Finally LPS enters the outer membrane of the cell through an opening between the red and blue strands of LptD.
A group from the University of East Anglia, University of St Andrews and Diamond Light Source have made a breakthrough in the race to solve antibiotic resistance. Using Diamond, one of the UK’s most advanced scientific machines which produces a light 10 billion times brighter than the sun, they studied ‘superdrug’ bacteria in extreme detail to identify an innovative method of disabling bacteria and preventing antibiotic resistance.
 
The discovery doesn’t come a moment too soon. The World Health Organisation has warned that antibiotic-resistance in bacteria is spreading globally, with severe consequences. Even common infections, which have been treatable for decades, can once again kill. This breakthrough is a giant leap forward in the fight against superbugs.
 
Bacteria are able to infect their hosts because they camouflage themselves against the immune system. However, this new research, published today in the journal Nature, reveals how the bacteria construct this camouflage and opens the door to blocking the process through new classes of antibiotics.
 
Researchers investigated Gram-negative bacteria, which cause a vast range of infections, including e-coli, salmonella, gonorrhea, pseudomonas, and meningitis. The outer surface of a Gram-negative bacterial cell acts as a disguising “cloak” that provides a barrier against toxic compounds such as antibiotics and camouflages the invading organism to evade detection and destruction by the body’s defences. Using the intense light produced by Diamond to study these bacteria at an atomic level, they were able to pinpoint the structure of the integral protein responsible for the final stage of creating the bacteria’s camouflage.

 

copyright @Neil Paterson 2014

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By determining the shape of this protein using Diamond’s synchrotron technology, the team has made it possible to design drugs that slot into the protein and stop it in its tracks, killing superbugs by simply disabling the camouflage. With this important defense barrier removed the bacteria cannot survive.
The findings are profoundly significant, because targeting the final stage of the camouflage assembly mechanism may be possible from the cell exterior, preventing the bacteria from simply pumping out the antibiotic and negating a key antibiotic resistance mechanism.
 
This protein is highly conserved across Gram-negative bacteria, suggesting that a wide range of bacterial pathogens could be attacked via this target. This means that in future, we may be able to take one drug to combat a vast range of infections.

Dr Neil Paterson (Diamond Light Source) collaborated on the project, providing in-house support whilst the group was using Diamond’s cutting-edge facilities to pinpoint the structure of the camouflage protein. He comments:
 
“This is an exciting structure that fundamentally advances our understanding of basic cell assembly and at the same time provides a detailed view of an intriguing target for new classes of antibiotics. We would not have been able to determine this structure without the facilities at a synchrotron such as Diamond.”
 
Group leader Prof Changjiang Dong, from UEA’s Norwich Medical School, said: “We have identified the path and gate used by the bacteria to transport the barrier building blocks to the outer surface. Importantly, we have demonstrated that the bacteria would die if the gate is locked.”
Schematic of the transport and assembly of the lipopolysaccharide (LPS) decorative cloak of Gram negative bacteria. A series of proteins, Lpt A,B,C,F and G shuttle LPS across the inner membrane of the cell and across the periplasm to the outer membrane where it is transferred to the LptDE complex. LptE guides LPS through the pore which then opens between the first and last strand (β1 and β26) to allow the base of LPS to enter the membrane and become part of the outer surface of the cell.
Schematic of the transport and assembly of the lipopolysaccharide (LPS) decorative cloak of Gram negative bacteria. A series of proteins, Lpt A,B,C,F and G shuttle LPS across the inner membrane of the cell and across the periplasm to the outer membrane where it is transferred to the LptDE complex. LptE guides LPS through the pore which then opens between the first and last strand (β1 and β26) to allow the base of LPS to enter the membrane and become part of the outer surface of the cell.
 
“This is really important because drug-resistant bacteria is a global health problem. Many current antibiotics are becoming useless, causing hundreds of thousands of deaths each year.
“The number of super-bugs are increasing at an unexpected rate. This research provides the platform for urgently-needed new generation drugs.”
 
Lead author PhD student Haohao Dong from the University of St Andrews said: “The really exciting thing about this research is that new drugs will specifically target the protective barrier around the bacteria, rather than the bacteria itself.
“Because new drugs will not need to enter the bacteria itself, we hope that the bacteria will not be able to develop drug resistance in future.”
 
This research was funded by Wellcome Trust. Research collaborators included Dr Phillip Stansfield from the University of Oxford, Prof Wenjan Wang of Sun Yat-sen University (China).
 
 
 
 
‘Structural basis for outer membrane lipopolysaccharide insertion’ published in the journal Nature on June 18, 2014.  The DOI is 10.1038/nature13464