Mechanism of ATP-Dependent Proteolysis by Lon Protease

Case Western Reserve University, Cleveland OH

Investigators

Abstract

The overall goal of this project is the elucidation of the mechanism of ATP (adenosine triphosphate-dependent proteolysis by Lon protease. Lon protease is an ATP-dependent serine protease complex functioning to maintain cellular homeostasis and relieve cell stress. This protease possesses an intrinsic ATPase activity that is elevated during protein degradation. The specific goal of this project is to determine how the chemical energy source ATP is used by Lon to catalyze protein degradation, and from here, obtain insights into why nature design proteases that utilize ATP as activators. In this project, the PI will perform kinetic experiments to identify enzyme intermediates, whose formations are dependent on ATP hydrolysis in the degradation pathway of an unstructured protein called lambda N, and determine their functions accordingly. The kinetic mechanisms of ATP binding and subsequent hydrolysis during lambda N degradation are evaluated by rapid chemical quench techniques. The kinetic mechanisms of ATP- versus AMPPNP-dependent cleavage of specific sites within lambda N are evaluated by fluorescence stopped flow technique. The kinetic mechanisms of ATP- versus AMPPNP-dependent translocation of a defined scissile site in lambda N to the proteolytic site of a bacterial Lon are evaluated through monitoring the fluorescence resonance energy transfer signal by stopped flow techniques. Results generated from this study will provide insight into the mechanism by which Lon couples its ATPase and peptidase activities to degrade an endogenous protein substrate lacking defined structure. This work will represent the first quantitative study designed to determine the contribution of the ATPase activity of Lon to protein degradation. Broader Impacts This project employs a multi-disciplinary approach to determine the mechanism of ATP-dependent proteolysis. As such, students participating in this project acquire a multidisciplinary training in enzyme kinetics, protein chemistry, liquid chromatography, mass spectrometry, chemical synthesis, solid phase peptide synthesis, fluorescence spectroscopy, protein purification and molecular cloning. These research activities provide excellent training opportunities to undergraduate and graduate students in biochemistry. Additionally, all personnel working in the PI's laboratory serve as volunteers to the National Youth Sports Program (NYSP). NYSP is summer program offered to children of low-income families in the Greater Cleveland area between the ages of 10 and 16. Participating students teach these children chemistry of daily life through experimentation with household chemicals and dry ice. This annual outreach activity has become a tradition in the PI's laboratory, where undergraduate and graduate students learn to become more involved in the community and education for the underprivileged.