Induced fit on sugar binding activates ribokinase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Ribokinase catalyzes the initial phosphorylation of ribose, a key step in its metabolic pathway.
• Previous structural data existed for the ternary complex of Escherichia coli ribokinase with ribose and ADP.

Purpose of the Study:

• To elucidate the conformational changes involved in ribokinase function through structural analysis.
• To understand the mechanism of substrate binding and catalysis in ribokinase.

Main Methods:

• X-ray crystallography was employed to determine structures of the apo enzyme, ribose-bound state, and four new ternary complex forms.
• Comparative structural analysis was performed to identify conformational differences.

Main Results:

• Structures reveal an open apo form that transitions to a closed conformation upon ribose binding, trapping the sugar.
• Nucleotide binding induces further, subtle structural adjustments in the enzyme.
• Evidence suggests lid movements in the ternary complex are essential for transition state formation and breakdown.

Conclusions:

• Conformational changes, both large and small, are critical for ribokinase activity.
• The observed structural dynamics provide insights into the catalytic mechanism of ribokinase and related carbohydrate kinases.
• These findings have implications for understanding enzyme function in sugar metabolism.