Chemically active soft matter
Biological matter is locally driven out of equilibrium by the action of enzymes, which catalyze the chemical reactions necessary for life. The chemicals produced and consumed range from short-lived reaction intermediates, to the essential molecules involved in energy storage, cell-cell communication, etc. An important question is then: How do these nanoscale enzymes manage to self-organize in order to drive non-equilibrium activity at the right place, and at the right time?
At the level of single enzymes, we develop microscopically-detailed models to understand how enzymes transduce their catalytic action into mechanical motion. Indeed, a number of recent experiments have shown that enzymes display both enhanced diffusive motion as well as directed motion (chemotaxis) in the presence of uniform concentrations and gradients of their chemical substrate, respectively. Guided by the experimental results, we aim to unravel the underlying mechanisms by constructing models that include all relevant ingredients, from hydrodynamics to thermal (and non-thermal) fluctuations.
At the level of many enzymes, we use both theory as well as computer simulations to understand collective behavior. In particular, the production and consumption of chemicals by the enzymes, coupled to their chemotactic response to these chemicals, leads to effective long ranged interactions between the enzymes. These effective interactions, which show telltale signs of non-equilibrium activity such as non-reciprocity (e.g. A is attracted to B, while B is repelled from A), can lead to a plethora of phase separation phenomena. The generic, minimal models that we develop may be applied not just to enzymes but also to other systems consisting of chemically-interacting particles, such as collections of cells and microorganisms, or artificial materials made from synthetic catalytically-active colloids.
Lastly, we use continuum theories of elasticity and capillarity to study how enzymatic activity couples to 'soft', deformable cellular components such as biomembranes and membraneless organelles. Indeed, enzymatic activity can drive dynamic processes such as growth or transport (e.g. through membrane channels, membrane fusion and fission...), which in turn may result in pattern formation and self-organization at length scales much larger than the nanometer length scale characteristic of enzymes.