Scientists find a never-seen-before protein structure in a virus

Two domains of the Chitosanase protein

From the analysis of captured images and gene sequence of the protein, the researchers could also classify the protein as one that resembled a group of carbohydrate metabolizing enzymes called glycosyl hydrolase GH45. However, the similarities between chitosanase and GH45 were limited. The bits that did not look like the GH45 family enzyme did not look like any other enzyme seen before either.

“There is a part of the enzyme that is completely new and novel. That’s what’s exciting to me as a structural biologist — to see something we have not seen before, and then try to figure out what its role might be”, Smith added in the press release.

This opens up more avenues of research to determine how the protein functions and its possible role in soil cycling. It would also help explore the role of AMGs and the role they play in interaction with other organisms in the soil.

The research findings were published in the journal Nature Communications.


Metagenomics is unearthing the previously hidden world of soil viruses. Many soil viral sequences in metagenomes contain putative auxiliary metabolic genes (AMGs) that are not associated with viral replication. Here, we establish that AMGs on soil viruses actually produce functional, active proteins. We focus on AMGs that potentially encode chitosanase enzymes that metabolize chitin – a common carbon polymer. We express and functionally screen several chitosanase genes identified from environmental metagenomes. One expressed protein showing endo-chitosanase activity (V-Csn) is crystalized and structurally characterized at ultra-high resolution, thus representing the structure of a soil viral AMG product. This structure provides details about the active site, and together with structure models determined using AlphaFold, facilitates understanding of substrate specificity and enzyme mechanism. Our findings support the hypothesis that soil viruses contribute auxiliary functions to their hosts.