Glucose-induced conformational change in yeast hexokinase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Yeast hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) exists as different isozymes, such as A and B.
• The enzyme's conformation is critical for its catalytic activity.
• Previous studies have investigated hexokinase structure and function.

Purpose of the Study:

• To compare the high-resolution structures of yeast hexokinase A complexed with glucose and yeast hexokinase B in its absence.
• To elucidate the conformational changes induced by glucose binding in hexokinase A.
• To analyze the role of hydrophobic interactions in stabilizing the enzyme's active conformation.

Main Methods:

• High-resolution structural analysis of yeast hexokinase A-glucose complex.
• Comparison with the structure of yeast hexokinase B.
• Estimation of hydrophobic contributions to free energy changes upon ligand binding.

Main Results:

• Yeast hexokinase A exhibits a distinct conformation when bound to glucose compared to hexokinase B without glucose.
• Glucose binding induces a 12-degree rotation between the molecule's lobes, closing the active site cleft.
• The hydrophobic effect favors the active conformation of hexokinase, both with and without glucose.

Conclusions:

• Glucose binding to yeast hexokinase A triggers an 'induced fit' conformational change essential for catalysis.
• The observed stability of the inactive conformation in the absence of substrate may be due to insufficient interactions within the closed cleft.
• Hydrophobic interactions play a significant role in stabilizing the enzyme's active state.