Allosteric modulation of the Lon protease by effector binding and local charges

Abstract

The ATPase Associated with diverse cellular Activities (AAA+) family of proteases play crucial roles in cellular proteolysis and stress responses. Like other AAA+ proteases, the Lon protease is known to be allosterically regulated by nucleotide and substrate binding. Although it was originally classified as a DNA binding protein, the impact of DNA binding on Lon activity is unclear. In this study, we characterize the regulation of Lon by single-stranded DNA (ssDNA) binding and serendipitously identify general activation strategies for Lon. Upon binding to ssDNA, Lons ATP hydrolysis rate increases due to improved nucleotide binding, leading to enhanced degradation of protein substrates, including physiologically important targets. We demonstrate that mutations in basic residues that are crucial for Lons DNA binding not only reduces ssDNA binding but result in charge-specific consequences on Lon activity. Introducing negative charge at these sites induces activation akin to that induced by ssDNA binding, whereas neutralizing the charge reduces Lons activity. Based on single molecule measurements we find that this change in activity is correlated with changes in Lon oligomerization. Our study provides insights into the complex regulation of the Lon protease driven by electrostatic contributions from either DNA binding or mutations. HighlightsO_LIssDNA binding allosterically activates Lon ATP hydrolysis C_LIO_LINegative charge at DNA binding site is sufficient for Lon activation C_LIO_LINeutralization of charge at DNA binding site inhibits Lon ATP hydrolysis C_LIO_LILon activity is linked to formation of stable Lon hexamers C_LI SignificanceThe energy-dependent protease Lon is integral in both eukaryotic and prokaryotic physiology, contributing to protein quality control, stress management, developmental regulation, and pathogenicity. The ability to precisely regulate protein levels through targeted degradation underscores a need for tunability. We find that single-stranded DNA (ssDNA) acts as an allosteric regulator of Lon, leading to enhanced enzymatic activity. Mutations in basic residues crucial for DNA binding were found to affect Lon activity in a charge-specific manner highlighting the importance of electrostatic interactions regulating Lons function. Changes in Lon activity due to ssDNA binding or mutations were correlated with its oligomerization state. Our findings provide insights into the activation strategies of Lon, emphasizing the role of electrostatic contribution that modulate nucleotide affinity, oligomerization and proteolysis to advance our understanding of the complex regulatory mechanisms of the Lon protease.