Diffusion properties of single FoF1-ATP synthases in a living bacterium unraveled by localization microscopy

TL;DR

This study measures the diffusion of single FoF1-ATP synthases in living E. coli using localization microscopy, revealing insights into enzyme organization and mobility in the bacterial membrane.

Contribution

It provides the first quantitative diffusion measurements of single ATP synthases in live bacteria, distinguishing monomeric from supercomplex-associated forms.

Findings

Diffusion coefficient D = 0.072 μm²/s for ATP synthases in E. coli

Application of localization microscopy and single enzyme tracking in bacteria

Consideration of membrane curvature in diffusion analysis

Abstract

FoF1-ATP synthases in Escherichia coli (E. coli) bacteria are membrane-bound enzymes which use an internal proton-driven rotary double motor to catalyze the synthesis of adenosine triphosphate (ATP). According to the 'chemiosmotic hypothesis', a series of proton pumps generate the necessary pH difference plus an electric potential across the bacterial plasma membrane. These proton pumps are redox-coupled membrane enzymes which are possibly organized in supercomplexes, as shown for the related enzymes in the mitochondrial inner membrane. We report diffusion measurements of single fluorescent FoF1-ATP synthases in living E. coli by localization microscopy and single enzyme tracking to distinguish a monomeric enzyme from a supercomplex-associated form in the bacterial membrane. For quantitative mean square displacement (MSD) analysis, the limited size of the observation area in the membrane with a significant membrane curvature had to be considered. The E. coli cells had a diameter of about 500 nm and a length of about 2 to 3 \mum. Because the surface coordinate system yielded different localization precision, we applied a sliding observation window approach to obtain the diffusion coefficient D = 0.072 \mum2/s of FoF1-ATP synthase in living E. coli cells.