( Scientists have made nisin a natural a...)Creation of antibiotic in test tube holds promise for better antibiotics

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. One of these is the cyclase wh
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Source:University of Illinois at Urbana-Champaign