Structural basis for glycogen recognition by AMP-activated protein kinase.

Area of Science:

• Biochemistry
• Structural Biology
• Cellular Metabolism

Background:

• AMP-activated protein kinase (AMPK) regulates cellular energy balance.
• The AMPK beta subunit scaffolds catalytic and regulatory subunits and targets the complex to glycogen.
• Understanding AMPK's interaction with glycogen is crucial for metabolic regulation.

Purpose of the Study:

• To determine the structure of the AMPK beta subunit's glycogen binding domain.
• To elucidate the mechanism of carbohydrate binding by the AMPK beta subunit.
• To investigate the role of specific residues in glycogen binding.

Main Methods:

• X-ray crystallography to determine the structure of the AMPK beta subunit in complex with beta-cyclodextrin.
• Site-directed mutagenesis to alter key binding residues.
• Biochemical assays to assess glycogen binding affinity.

Main Results:

• The crystal structure revealed a unique carbohydrate-binding pocket within the AMPK beta subunit.
• This pocket accommodates multiple glucose units, similar to starch-binding domains, with specific tryptophan and leucine residues involved in binding beta-cyclodextrin.
• Mutations in key residues abolished or reduced glycogen binding, confirming their importance.
• Modeling indicated the pocket allows AMPK to bind glycogen along its helical surface.

Conclusions:

• The AMPK beta subunit possesses a distinct carbohydrate-binding pocket essential for glycogen interaction.
• This structural and functional characterization provides a molecular basis for how AMPK senses and responds to cellular energy status via glycogen.
• The findings offer potential targets for modulating AMPK activity in metabolic diseases.