Cellular dynamics of the SecA ATPase at the single molecule level

Area of Science:

• Bacterial protein secretion
• Molecular mechanisms of protein translocation
• Cellular dynamics and membrane association

Background:

• The SecA ATPase powers protein translocation through the SecYEG translocon in bacteria.
• Understanding SecA's association with the SecYEG translocon in vivo remains challenging due to the crowded cellular environment.

Purpose of the Study:

• To visualize the single-molecule dynamics of SecA in Escherichia coli using super-resolution microscopy.
• To elucidate the association and movement of SecA with the bacterial cell membrane and its role in protein secretion.

Main Methods:

• Single-molecule super-resolution microscopy in live Escherichia coli.
• Analysis of SecA dynamics and localization under varying cellular conditions.

Main Results:

• SecA predominantly exists as a homodimer associated with the cytoplasmic membrane, with a small cytosolic fraction.
• SecA exhibits three interconvertible diffusional states: loosely membrane-associated, integral membrane, and temporarily immobile.
• Disruption of the proton-motive force leads to SecA relocalization to the cytoplasm and transient membrane localization.

Conclusions:

• SecA diffuses along the bacterial cell membrane surface to reach the SecYEG translocon.
• The proton-motive force is critical for maintaining SecA's membrane association and function in protein secretion.