Enterococcus faecalis α1-2-mannosidase (EfMan-I): an efficient catalyst for glycoprotein N-glycan modification

Area of Science:

• Enzymology
• Glycobiology
• Structural Biology

Background:

• Vertebrate glycoprotein N-glycan maturation requires multiple α1-2-mannosidases.
• Bacterial α1-2-mannosidases can singularly cleave α1-2-linked mannose residues in host N-glycans.

Purpose of the Study:

• To characterize a new α1-2-mannosidase (EfMan-I) from Enterococcus faecalis.
• To determine the crystal structure of EfMan-I and understand its catalytic mechanism.
• To evaluate EfMan-I's potential for in vitro N-glycan modification.

Main Methods:

• Enzyme characterization of EfMan-I.
• Determination of the crystal structure of EfMan-I at 2.15 Å resolution.
• Analysis of substrate specificity, including oligomannoses and high-mannose-type N-glycans.

Main Results:

• EfMan-I, from Enterococcus faecalis, efficiently cleaves α1-2-mannose residues.
• The crystal structure reveals a two-domain fold characteristic of CAZy GH92 mannosidases.
• An unusual potassium ion was identified bridging the enzyme's domains near the active site.

Conclusions:

• EfMan-I is a potent bacterial α1-2-mannosidase capable of modifying N-glycans on glycoproteins.
• The structural insights, including the potassium ion, aid in understanding its catalytic function.
• EfMan-I shows significant promise as a catalyst for in vitro N-glycan engineering of high-mannose-type structures.