Nonrigid enzymes structured discovered by MIT chemists

 

A research funded by the National Institutes of Health and the French National Research Agency and ccarried out by MIT researchers have shown that some of the atoms in an enzyme called carbon monoxide dehydrogenase can rearrange themselves when oxygen levels are low.

This enzymes have become of great interest to researchers who want to find new ways to remove greenhouse gases from the atmosphere and turn them into useful carbon-containing compounds

Many microbes have an enzyme that can convert carbon dioxide to carbon monoxide. This reaction is critical for building carbon compounds and generating energy, particularly for bacteria that live in oxygen-free environments.

At MIT, Brandeis University, and Aix-Marseille University in France, Drennan and her colleagues have discovered a unique aspect of the structure of the “C-cluster”. C-cluster is the collection of metal and sulfur atoms that forms the heart of the enzyme carbon monoxide dehydrogenase (CODH). Instead of forming a rigid scaffold, as had been expected, the cluster was found to change its configuration.

Drennan began studying the structure of carbon monoxide dehydrogenase and the C-cluster about 20 years ago, soon after she started her lab at MIT. She and another research group each came up with a structure for the enzyme using X-ray crystallography, but the structures weren’t quite the same. The differences were eventually resolved and the structure of CODH was thought to be well-established.

From the researchers analysis there are two different structures for the C-clusters. The arrangement of the first structure was quite expected. It is a cube with four sulfur atoms, three iron atoms, and a nickel atom, the fourth iron atom is connected to the cube.

In the second structure, however, the nickel atom is removed from the cube-like structure and takes the place of the fourth iron atom. The displaced iron atom binds to a nearby amino acid, cysteine, which holds it in its new location. One of the sulfur atoms also moves out of the cube. All of these movements appear to occur in unison, in a movement the researchers describe as a “molecular cartwheel.”

It was believed that this movement, which occurs upon oxygen exposure, helps to protect the cluster from completely and irreversibly falling apart in response to oxygen.

Accordinding to Drennan,“In the past, people thought of these clusters as really being these rigid scaffolds, but just within the last few years there’s more and more evidence coming up that they’re not really rigid.”

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