Glycogen Phosphorylase

PDB file 6GPB

This structure of rabbit muscle Glycogen Phosphorylase in the tense conformation with bound substrate analog was determined by K. R. Acharya & L. N. Johnson in 1990. Only a single subunit of the dimer is shown.

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Display the protein as ribbons.

Select hetero-ligand, display as ball & stick, and color CPK.
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Identify each ligand shown below by its chemical structure.
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AMP is bound at two regulatory sites.

Identify heptulose-2-phosphate (998), an analog of the product glucose-1-phosphate, at the active site. 

Also at the active site, pyridoxal phosphate (PLP, see above), is joined via Schiff base linkage to the terminal amino group of lys680.
Use the command line to select this amino acid.
Then alter its display and color it CPK.
Look for the linkage between the N of Lys680 and C of PLP. 

Note the proximity of the phosphate of PLP (involved in acid base catalysis) and the phosphate of the heptulose-2-phosphate product analog.

Questions:
1. How does the distance from the glycogen storage site (location of bound chain of glucose residues) to the active site relate to the length of the "limit branch"?
2. Is Ser14, whose hydroxyl is phosphorylated via Phosphorylase Kinase, located at the active site?

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