Regulation Of Enzymatic Activity Occurs By Selection Of Discrete Activity States

Tight regulation of enzymatic activity is crucial for controlling a multitude of fundamental cellular processes. Yet the molecular level details underlying regulation often remain poorly understood (1). Here we employed single molecule activity studies to dissect the mechanistic origin of regulation of enzymatic activity (2). As a model system we employed a lipase and measured its activity as a function of accessibility to surface tethered liposomes (3,4), which are known regulators of its activity. Our results surprisingly revealed that the lipase does not follow a continuous distribution of activity rates (5,6) but rather oscillates between 2 states of different activity as the majority of signaling protein and ion channels do (1). We accurately quantified for the first time both the interconversion rates between the 2 states and their inherent activity. Based on these we calculated the energetic landscape of the entire reaction pathway and identified that regulation of enzymatic activity does not occur via an increase in the enzymes inherent activity but rather predominantly originates from increased time spent on the highly active state. Because we found a number of structurally unrelated enzymes to exhibit an analogous behavior we anticipate that oscillation between a discrete number of activity states rather than a between a continuous distribution of them might be a generic mechanism potentially facilitating regulation of enzymatic activity. 1. Gardino A.K et al., Cell, 139, 1109 (2009). 2. N. S Hatzakis, et al., submitted 3. N. S. Hatzakis et al., Nat. Chem. Biol., 5, 835 (2009). 4. D. Stamou, C. et al., Angew. Chem. Int. Ed., 42, 5580 (2003). 5. N. S. Hatzakis et al., Chem Commun, 2012 (2006). 6. B. P. English et al., Nat Chem Biol, 2, 168 (2006).