Asymmetry and structural changes in ECF1 examined by cryoelectronmicroscopy

Area of Science:

• Structural Biology
• Biochemistry
• Molecular Motors

Background:

• The Escherichia coli F1-ATPase (ECF1) is a key enzyme responsible for ATP hydrolysis.
• Understanding the spatial arrangement and dynamics of its subunits is critical for elucidating its mechanism.
• Previous studies indicated potential movement of subunits during catalysis.

Purpose of the Study:

• To determine the three-dimensional structure and subunit arrangement of ECF1 using cryo-electron microscopy.
• To investigate the positional dynamics of the gamma and epsilon subunits within the ECF1 complex.
• To explore the nucleotide dependence of subunit positioning.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to visualize the ECF1 complex.
• Image analysis techniques were used to distinguish individual beta subunits based on projection density.
• Site-directed mutagenesis and gold particle labeling were utilized to track the epsilon subunit's position.

Main Results:

• Intrinsic asymmetry was identified in the hexagonal projection of ECF1, allowing differentiation of the three beta subunits (β1, β2, β3).
• The gamma subunit's position was not fixed, exhibiting an arc-like shift of approximately 10Å relative to the center of mass, potentially dependent on nucleotide binding.
• The epsilon subunit was localized to an arc between an alpha and a beta subunit, with a shift of approximately 20Å, and its position demonstrated nucleotide dependence.

Conclusions:

• The study successfully mapped the positions of the gamma and epsilon subunits within the ECF1 complex.
• Evidence is presented for nucleotide-dependent positional changes of the epsilon subunit, complementing known nucleotide dependence of the gamma subunit.
• These findings provide insights into the conformational flexibility and dynamic mechanism of rotary ATPases.