ABCE1 Controls Ribosome Recycling by an Asymmetric Dynamic Conformational Equilibrium

Abstract

Summary: The twin-ATPase ABCE1 has a vital function in mRNA translation by recycling terminated or stalled ribosomes. As for other functionally distinct ATP-binding cassette (ABC) proteins, the mechanochemical coupling of ATP hydrolysis to conformational changes remains elusive. Here, we use an integrated biophysical approach allowing direct observation of conformational dynamics and ribosome association of ABCE1 at the single-molecule level. Our results from FRET experiments show that the current static two-state model of ABC proteins has to be expanded because the two ATP sites of ABCE1 are in dynamic equilibrium across three distinct conformational states: open, intermediate, and closed. The interaction of ABCE1 with ribosomes influences the conformational dynamics of both ATP sites asymmetrically and creates a complex network of conformational states. Our findings suggest a paradigm shift to redefine the understanding of the mechanochemical coupling in ABC proteins: from structure-based deterministic models to dynamic-based systems. : Gouridis et al. delineate the inner workings of ABCE1 by single-molecule FRET, demonstrating that the two asymmetric nucleotide-binding sites functionally and conformationally adopt distinct states during ribosome recycling. Unexpectedly, both sites are found in a dynamic equilibrium of conformational states governed by ribosomes, nucleotides, and release factors. Keywords: ABC proteins, conformational dynamics, mRNA translation, mRNA surveillance, molecular motors, ribosome recycling, single-molecule FRET, twin ATPases