Long-Range Destabilizing Effects of Mutations at the Escherichia coli β Clamp Dimer Interface

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The β sliding clamp is a key bacterial processivity factor for DNA polymerase III.
• It tethers the polymerase to DNA, enhancing replication efficiency and processivity.
• Clamp loading involves a multi-subunit complex loading the dimeric β clamp onto DNA.

Purpose of the Study:

• To investigate the role of specific residues (Q265, R269) in the β clamp dimer interface stability and function.
• To determine if mutating these residues could rescue the activity of a destabilized L82D β clamp variant.
• To elucidate the contribution of noncovalent interactions to β clamp dimer stability.

Main Methods:

• Site-directed mutagenesis of β clamp residues (Q265, R269) in both wild-type and L82D backgrounds.
• Assays to evaluate clamp thermostability, dimerization state, and DNA loading activity.
• Molecular modeling to analyze structural changes and interaction networks.

Main Results:

• The R269 residue is critical for maintaining β clamp dimer stability, oligomeric state, and DNA loading.
• Mutation Q265A was tolerated, indicating Q265 is not essential for these functions.
• Disruption of R269 interactions in the L82D variant, forming alternative networks, correlated with reduced stability and activity.

Conclusions:

• A delicate balance of noncovalent interactions governs the stability of the β sliding clamp dimer interface.
• Specific residues, particularly R269, play crucial roles in maintaining clamp integrity and function.
• Understanding these interactions provides insights into DNA replication mechanisms and potential therapeutic targets.