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Creation of antibiotic in test tube holds promise for better antibiotics
Jim Barlow,
Life Sciences Editor
217-333-5802; jebarlow@uiuc.edu
3/9/06
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CHAMPAIGN, Ill.
— Scientists have made nisin, a natural antibiotic used for more
than 40 years to preserve food, in a test tube using nature’s
toolbox. They also identified the structure of the enzyme that makes
nisin and gives it its unique biological power.
The work – published in the March 10 issue of Science –
sheds light on the almost magical manner in which nisin is made in nature
and moves researchers closer to producing new antibiotics that would
preclude the development and spread of antibiotic-resistant bacteria,
said Wilfred A. van der Donk, a professor of chemistry,
and Satish Nair, a professor of biochemistry,
both at the University of Illinois at Urbana-Champaign.
Nisin, a peptide, contains 34 amino acid residues and the unusual amino
acids lanthionine, methyllanthionine, dehydroalanine and dehydro-amino-butyric
acid. The latter are made by post-translational modification of proteins.
Nisin works well against Gram-positive bacteria and food-borne pathogens
that cause botulism and listeriosis because it punches holes into cell
membranes and binds to essential molecules in the disease-causing bacteria.
Hitting on at least two targets reduces the risk of resistance occurring,
van der Donk said.
The researchers synthesized nisin simply in a test tube by using a single
cyclase enzyme to re-create the process that normally occurs in a strain
of the bacterium Lactococcus lactis found naturally in milk. They demonstrated
how just one protein (NisC) makes 10 new chemical bonds in a stereochemically
defined fashion. Specifically, they showed that NisC is responsible
for the formation of five characteristic thioether rings required for
nisin’s biological activity.
“Despite all the progress in synthetic chemistry, we cannot come
close to making a compound like nisin efficiently,” van der Donk
said.
“Synthetic chemists in the past needed 67 steps to make it, while
nature uses just two enzymes,” van der Donk added. “One
of these is the cyclase whose activity we have demonstrated in this
paper.”
The thioether rings vary in size from four to seven amino acids and
provide sturdy protease-resistant bonds at precise locations. They account
for nisin’s robust resistance capability. It was theorized that
one enzyme makes all five rings despite their very different sizes,
but how it did so was like the mystery of a magic show, van der Donk
said.
Nisin is one of numerous members of a family of compounds called lantibiotics,
all of which are candidates for bioengineering into new pharmaceuticals,
van der Donk said. The key is learning more about the enzymes involved
in their biosynthesis. “Our work, while not explaining everything,
has brought us much closer to that understanding, in particular the
beautiful structure solved by the Nair group,” he said.
Van der Donk previously identified the molecular activity of another
enzyme (LctM) responsible for naturally turning a small protein into
a lantibiotic. That discovery, reported in Science in 2004, involved
lacticin 481.
The new research also showed that NisC has unexpected structural similarities
with mammalian farnesyl transferases, which are important for the activity
of the RAS protein which when mutated is implicated in 25 percent of
breast cancers. Preventing farnesylation possibly could prevent the
cancerous effects, because the mutant protein would no longer be localized
at the membrane, Nair said.
An accompanying Perspectives article in Science, written by chemist
David W. Christianson of the University of Pennsylvania, suggests that
nisin’s five thioether rings may turn out to be golden “in
the never-ending search for blockbuster antibiotics.”
Joining van der Donk and Nair on the research, funded primarily by the
National Institutes of Health, were Bo Li, a biochemistry doctoral student
in van der Donk’s group; John Paul J. Yu, an M.D.-Ph.D student
in the Nair group; Joseph S. Brunzuelle of Argonne National Labs; and
Gert N. Moll of BiOMaDe Technology Foundation in the Netherlands.
