Related Experiment Videos
Parallel evolution in two homologues of phosphorylase
1Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448, USA.
Nature Structural Biology
|October 1, 1994
Summary
The structure of inactive yeast glycogen phosphorylase reveals a unique amino-terminal extension that blocks substrate access. Phosphorylation may release this block, activating the enzyme.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Yeast glycogen phosphorylase (GPh) is a key enzyme in glycogen metabolism.
- Understanding its inactive structure is crucial for elucidating its regulation.
- Comparison with muscle glycogen phosphorylase offers insights into conserved and unique regulatory mechanisms.
Purpose of the Study:
- To determine the high-resolution crystal structure of the unphosphorylated, inactive yeast glycogen phosphorylase.
- To compare the structural features of the inactive yeast enzyme with the active muscle enzyme.
- To identify structural elements responsible for the enzyme's inactive state.
Main Methods:
- X-ray crystallography was used to determine the structure.
- The resolution achieved was 2.6 A.
- Comparative structural analysis was performed.
Main Results:
- The unphosphorylated yeast glycogen phosphorylase structure was determined at 2.6 A resolution.
- The enzyme adopts a closed, substrate-excluding conformation, similar to inactive muscle glycogen phosphorylase.
- A unique 40-residue amino-terminal extension in yeast GPh binds near the catalytic site, hindering domain movement.
Conclusions:
- The N-terminal extension is a key structural feature responsible for maintaining yeast glycogen phosphorylase in an inactive state.
- Phosphorylation is proposed to displace the N-terminal extension, facilitating domain separation and substrate access.
- This mechanism highlights a unique regulatory strategy in yeast glycogen phosphorylase compared to its muscle counterpart.