Ligatin binds phosphohexose residues on acidic hydrolases

Area of Science:

• Biochemistry
• Cell Biology
• Glycobiology

Background:

• Ligatin is a receptor involved in recognizing phosphorylated sugars.
• Acidic hydrolases, including N-acetyl beta-D-glucosaminidase (beta-NAG), can be solubilized with ligatin.
• The interaction between ligatin and beta-NAG is crucial for understanding cellular recognition mechanisms.

Purpose of the Study:

• To investigate the binding characteristics of beta-NAG to ligatin.
• To determine the role of specific phosphorylated sugars in the dissociation of beta-NAG-ligatin complexes.
• To elucidate the nature of the phosphorylated moiety on beta-NAG.

Main Methods:

• Isolation of ligatin from plasma membranes of mouse macrophages, rat ileum, and rat brain.
• Solubilization of acidic hydrolases, including beta-NAG, with ligatin.
• Affinity chromatography to demonstrate beta-NAG binding to immobilized ligatin.
• Dissociation assays using mannose 6-phosphate (Man6P) and glucose 1-phosphate (Glc 1P).
• Enzymatic treatments with endoglucosaminidase H and alkaline phosphatase.

Main Results:

• Solubilized beta-NAG bound to ligatin, forming stable complexes.
• Complex dissociation varied significantly based on the enzyme source and specific phosphosugar used (Man6P or Glc 1P).
• Macrophage beta-NAG-ligatin complexes showed a strong preference for Glc 1P dissociation, while ileal complexes preferred Man6P.
• Enzymatic treatment suggested a phosphodiester linkage on beta-NAG, resistant to alkaline phosphatase but sensitive to endoglucosaminidase H.

Conclusions:

• The interaction between ligatin and beta-NAG is specific and influenced by the enzyme's origin.
• Beta-NAG likely possesses a unique phosphodiester structure, analogous to other lysosomal enzymes, mediating its interaction with ligatin.
• These findings contribute to understanding the molecular basis of ligand-receptor interactions involving phosphorylated glycans.