Scientists Discover a Unique Aspect of Enzyme Structure


Many microbes contain an enzyme essential for conversion of carbon dioxide into carbon monoxide. Such reaction is very crucial for generating energy and building carbon compounds, especially for bacteria living in anaerobic environment.

Scientists have been taking a lot of interest in such enzymes of microbes in order to discover new ways to remove greenhouse gas from the atmosphere and transformed them into carbon-containing compounds.

Catherine Drennan, a professor of biology and chemistry at MIT said, industrial processes for transforming carbon dioxide are energy-intensive which requires high temperature and pressure whereas the enzymes can conduct the same process at normal temperature. In a recent study, Drennan and other research group at MIT have found a distinct aspect of the structure of the ‘C-cluster’, a group of sulfur and metal atoms that forms the central part of the enzyme CODH (Carbon monoxide dehydrogenase). The scientists noticed an ability of the cluster to alter its configuration while it was expected to form a thick scaffold.

Clusters that consist of metals including C-cluster are capable of performing several important reactions in microbial organisms such as breaking down of nitrogen gas molecules, which is nearly impossible to recreate industrially.

Drennan has been studying the structure of C-cluster and CODH from the last 20 years. She and other scientist group used X-ray crystallography and each created a structure for the enzyme, but the structures weren’t exactly the same. Eventually, the differences were resolved and came up with well-established structure of enzyme CODH.

A few years ago, Wittenborn studied the project to understand sensitivity of the enzyme to oxygen inactivation and to determine the setup of C-cluster. The analysis has resulted into two distinct structures for the C-cluster:

1st Structure: A cube comprising of four sulfur atoms, a nickel atom, and three iron atoms, with a fourth one connected to the cube.

2nd Structure: In the cube-like structure, the nickel atom is removed and replaces the fourth iron atom. This displaced iron atom then binds with an adjacent amino acid and holds it in its new region while a sulfur atom goes out of the cube. Occurrence of all the movements are in unison and it is called as ‘molecular cartwheel’.

According to the researchers, movement of atoms occurs upon the exposure of oxygen, which is believed to prevent the cluster from degenerating in response to oxygen.

Apart from this largest metal shift of enzyme cluster, certain rearrangements were also found in some enzymes including metal cluster in enzyme nitrogenase, which is required for the conversion of nitrogen gas into ammonia.

Drennan said that understanding more about the unique structure of these clusters, how they react to oxygen exposure, and how they are assembled could help the scientists who are trying replicate their action for industrial application. This would provide a better chance to mimic the biological system and reduce the accumulation of greenhouse gas, she added.

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Rahul Pandita

Rahul Pandita

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