Functionally important movements in RecA molecules and filaments: studies involving mutation and environmental...

Area of Science:

• Structural Biology
• Molecular Biology
• Biochemistry

Background:

• RecA proteins are crucial for DNA repair and recombination.
• Understanding RecA filament dynamics is key to deciphering its function.
• The role of specific residues, like Gln196 in MsRecA, in RecA filament activation is not fully understood.

Purpose of the Study:

• To elucidate the structural basis of Gln196's role in Mycobacterium smegmatis RecA (MsRecA) filament activation.
• To characterize the conformational changes in MsRecA upon nucleotide binding in wild-type and mutant forms.
• To provide insights into the allosteric transitions of the RecA filament.

Main Methods:

• Determination of crystal structures of wild-type and mutant MsRecA (Gln196 to Ala, Asn, Glu) and their nucleotide complexes.
• Utilized low-temperature and room-temperature X-ray diffraction data.
• Analysis of 19 newly determined and 11 previously reported MsRecA structures.

Main Results:

• Nucleotide binding induces a movement of Gln196 towards the nucleotide in wild-type MsRecA, a movement abolished in mutants.
• Established the structural basis for Gln196's triggering action, dependent on side chain properties.
• Correlated C-terminal domain movements with LexA-binding loop and other domain movements, defining early stages of allosteric transformation.

Conclusions:

• Gln196 acts as a switch residue, its movement upon nucleotide binding being critical for MsRecA activation.
• The study reveals molecular plasticity in RecA filaments, essential for transitions to active states.
• These findings contribute to understanding the structural trajectory of RecA filament allosteric transformations.