Structural and mutagenic analysis of the RM controller protein C.Esp1396I

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Bacterial restriction-modification (RM) systems use DNA methylation and restriction to defend against foreign DNA.
• Controller (C) proteins regulate RM system genes, often acting as transcriptional regulators.
• Previous studies on C.Esp1396I provided insights into amino acid-DNA interactions.

Purpose of the Study:

• To investigate the role of key DNA-binding residues in the C.Esp1396I controller protein.
• To determine the impact of specific mutations on DNA binding affinity and protein structure.
• To compare DNA bending in native and mutant C.Esp1396I complexes.

Main Methods:

• Site-directed mutagenesis of C.Esp1396I DNA-binding residues.
• DNA binding affinity assays (e.g., surface plasmon resonance).
• High-resolution X-ray crystallography of mutant and native protein-DNA complexes.

Main Results:

• Mutations to base-interacting residues (T36, R46) significantly reduced DNA binding affinity compared to mutations of backbone-interacting residues (Y37, S52).
• Protein fold remained intact after mutations, but flexible loop conformations varied, affecting DNA sequence recognition.
• The Y37F mutation's structure revealed altered DNA bending compared to the native complex.

Conclusions:

• Base-interacting residues are more critical for C.Esp1396I DNA binding affinity than backbone-interacting residues.
• Mutations can alter DNA recognition through changes in flexible loop conformations and DNA bending.
• Structural and binding data elucidate the molecular mechanisms of C.Esp1396I function.