Subunit rotation in single FRET-labeled F1-ATPase hold in solution by an anti-Brownian electrokinetic trap

TL;DR

This study extends the observation time of single FRET-labeled F1-ATPase in solution by using a modified anti-Brownian electrokinetic trap, enabling detailed analysis of subunit rotation dynamics.

Contribution

It introduces a modified ABELtrap for prolonged single-molecule FRET observation of F1-ATPase in solution, enhancing the ability to analyze rotary motion.

Findings

Monte Carlo simulations show effective analysis of FRET changes with Hidden Markov Models.

The modified ABELtrap reduces background noise, improving signal detection.

Prolonged observation enables detailed kinetic studies of enzyme rotation.

Abstract

FoF1-ATP synthase catalyzes the synthesis of adenosine triphosphate (ATP). The F1 portion can be stripped from the membrane-embedded Fo portion of the enzyme. F1 acts as an ATP hydrolyzing enzyme, and ATP hydrolysis is associated with stepwise rotation of the gamma and epsilon subunits of F1. This rotary motion was studied in great detail for the last 15 years using single F1 parts attached to surfaces. Subunit rotation of gamma was monitored by videomicroscopy of bound fluorescent actin filaments, nanobeads or nanorods, or single fluorophores. Alternatively, we applied single-molecule F\"orster resonance energy transfer (FRET) to monitor subunit rotation in the holoenzyme FoF1-ATP synthase which was reconstituted in liposomes. Now we aim to extend the observation times of single FRET-labeled F1 in solution using a modified version of the anti-Brownian electrokinetic trap (ABELtrap) invented by A. E. Cohen and W. E. Moerner. We used Monte Carlo simulations to reveal that stepwise FRET efficiency changes can be analyzed by Hidden Markov Models even at the limit of a low signal-to-background ratio that was expected due to high background count rates caused by the microfluidics of the ABELtrap.