Altering the carbohydrate-binding specificity of the legume lectin FRIL through structure-guided engineering
Yo-Min Liu1, Hong Thuy Vy Nguyen1, Xiaorui Chen1
1Genomics Research Center, Academia Sinica, Taipei, Taiwan.
Nature Communications
|March 5, 2026
Summary
FRIL, a legume lectin, exhibits antiviral properties and binds complex N-glycans. Researchers found that loop B in the carbohydrate recognition domain (CRD) dictates specificity, differentiating between complex and high-mannose N-glycans.
Area of Science:
- Biochemistry
- Structural Biology
- Glycobiology
Background:
- FRIL is a legume lectin from hyacinth bean with broad-spectrum antiviral activity.
- FRIL distinguishes itself from other mannose/glucose-specific lectins by its specificity for complex type N-glycans.
- An extended binding site on FRIL is hypothesized to mediate this ligand selectivity.
Purpose of the Study:
- To investigate the structural basis for FRIL's complex N-glycan specificity.
- To identify the key regions within FRIL responsible for differentiating between complex and high-mannose N-glycans.
- To establish a method for activating recombinant FRIL and related lectins.
Main Methods:
- Activation of inactive recombinant FRIL (rFRIL) and proConcanavalin A (rproConA) via deglycosylation.
- Determination of cryo-electron microscopy (cryo-EM) structures of inactive apo rFRIL, active FRIL with a complex tetrasaccharide, and active rFRIL with a Man9 N-glycan.
- Site-directed mutagenesis involving swapping of loop B and loop C residues between FRIL and Concanavalin A (ConA).
Main Results:
- Deglycosylation was confirmed as a method to activate inactive recombinant legume lectins.
- Cryo-EM structures revealed residues H102 and Y101 on loop B of FRIL are critical for recognizing complex glycans.
- A FRIL mutant with swapped loop B and C residues exhibited exclusive binding to high-mannose N-glycans, unlike wild-type FRIL.
Conclusions:
- Legume lectin carbohydrate recognition domain (CRD) loop B is a primary determinant of N-glycan specificity.
- Deglycosylation serves as a viable activation strategy for recombinant FRIL and similar lectins.
- Specific residues within loop B are crucial for establishing oligosaccharide binding preferences, enabling the design of lectins with tailored specificities.
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