Essential Functional Interplay of the Catalytic Groups in Acid Phosphatase

Area of Science:

• Biochemistry
• Enzyme catalysis
• Protein engineering

Background:

• Enzyme active sites feature functional devices crucial for catalysis.
• Understanding enzyme efficiency is key for enzyme design and engineering.

Purpose of the Study:

• Investigate the functional interplay of the catalytic nucleophile (His18) in acid phosphatase.
• Analyze the impact of replacing histidine with aspartate on enzyme activity and mechanism.

Main Methods:

• Crystallography
• Biochemical assays
• Computational simulations (Empirical Valence Bond)
• Linear free-energy relationships

Main Results:

• A conserved mechanism via a phospho-enzyme intermediate was observed for Asp18.
• Cooperativity between nucleophile and acid groups was evident in wild-type but lost in the H18D variant.
• Histidine offers a ~10^4-fold advantage over aspartate as a nucleophile, with cooperativity adding ≥10^2-fold.

Conclusions:

• The cooperative interplay of active site residues is essential for high phosphatase efficiency.
• Loss of cooperativity in the H18D variant is due to impaired substrate positioning and altered leaving group protonation.
• Enzymatic catalysis differs from solution reactions due to electrostatic preorganization and cooperative effects.