News Sci/Tech Sweet Insights: How Insects Detect Sugars
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Genetics

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The molecular basis of sugar detection by an insect taste receptor

Animals crave sugars due to their energy potential and the delightful sensation of sweetness. However, not all sugars are metabolically equal, necessitating mechanisms to discern and differentiate chemically similar sweet substances. Insects employ a family of ionotropic gustatory receptors to discriminate sugars, each selectively activated by specific sweet molecules.

Unlocking the Secrets of Sugar Selectivity

To unravel the molecular basis of sugar selectivity, researchers delved into the structure of Gr9, a gustatory receptor found in the silkworm Bombyx mori (BmGr9). By examining Gr9's structures in the absence and presence of its sole activating ligand, D-fructose, they made intriguing discoveries.

Enveloped by a Ligand-Binding Pocket

The structure of BmGr9 revealed that D-fructose nestles within a ligand-binding pocket, precisely matching the overall shape and chemical groups of the sugar. Yet, computational docking and binding assays unveiled that other sugars also bind BmGr9 without activating the receptor.

The Crucial Role of Aromatic Residues

Further investigations showed that while both D-fructose and another non-activating sugar, L-sorbose, bind at a similar position, only D-fructose engages a bridge of two conserved aromatic residues. This interaction induces a conformational change, allowing the ion-conducting pore to open. Thus, chemical specificity emerges not solely from the ligand-binding pocket but from a combination of factors.

These findings shed light on how insects perceive sweetness, offering insights into their dietary preferences and ecological interactions.

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