Structure and Activity of a β-Mannosidase Involved in Core N-Glycan Degradation

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• N-glycans are crucial for glycoprotein function in eukaryotes.
• Bacteria possess pathways to degrade N-glycans for nutrients.
• Glycoside hydrolase family 5 subfamily 18 (GH5_18) enzymes cleave the N-glycan core.

Purpose of the Study:

• To biochemically and structurally characterize MoGH5_18, a GH5_18 enzyme.
• To understand the role of MoGH5_18 in bacterial N-glycan degradation.
• To explore conserved enzymatic mechanisms in glycan breakdown.

Main Methods:

• Biochemical assays to determine enzyme activity and substrate specificity.
• X-ray crystallography to solve the 3D structure of MoGH5_18.
• Bioinformatic analysis of gene clusters involved in N-glycan metabolism.

Main Results:

• MoGH5_18 specifically hydrolyzes the Manβ1-4GlcNAc disaccharide.
• The crystal structure reveals a dimeric (β/α) 8 TIM-barrel fold with a conserved active site.
• MoGH5_18 shares structural and functional characteristics with other GH5_18 enzymes despite sequence divergence.

Conclusions:

• MoGH5_18 is a functional GH5_18 enzyme involved in N-glycan degradation.
• The study highlights the utility of SSN-guided approaches for discovering enzymatic mechanisms.
• Conserved enzymatic strategies exist across diverse bacterial glycan degradation pathways.