X-ray structure of Glu 53 human lysozyme

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Human lysozyme (HL) is a key enzyme in innate immunity.
• Understanding enzyme structure-function relationships is crucial for drug development.
• Site-directed mutagenesis is a powerful tool to probe enzyme mechanisms.

Purpose of the Study:

• To determine the three-dimensional structure of a modified human lysozyme (Glu 53 HL).
• To elucidate the structural basis for altered catalytic activity in Glu 53 HL.
• To investigate the role of residue 53 in human lysozyme's catalytic mechanism.

Main Methods:

• X-ray crystallography was used to determine the structure of Glu 53 HL at 1.77 A resolution.
• Comparison of the three-dimensional structures of Glu 53 HL and wild-type HL.
• Analysis of the active site region, including hydrogen bonding networks and residue positioning.

Main Results:

• The overall backbone structure of Glu 53 HL is highly similar to wild-type HL (RMSD of 0.141 A).
• The active site structure is largely conserved, explaining similar substrate binding abilities.
• The mutation causes a positional and orientational change of the carboxyl group at residue 53, leading to significantly reduced catalytic activity (approx. 1%).

Conclusions:

• The precise positioning of the carboxyl group at residue 53 is critical for efficient catalysis.
• The Glu 53 residue likely plays a role beyond simple electrostatic stabilization of reaction intermediates.
• This study highlights the sensitivity of enzyme function to subtle structural changes in the active site.