Membraneless Compartmentalization Facilitates Enzymatic Cascade Reactions and Reduces Substrate Inhibition

Living cells possess membraneless organelles formed by liquid-liquid phase separation. With the aim of better understanding the general functions of membraneless microcompartments, this paper constructs acellular multicompartment reaction systems using an aqueous multiphase system. Membraneless coacervate droplets are placed within a molecularly crowded environment, where a larger dextran (DEX) droplet is submerged in a polyethylene glycol (PEG) solution. The coacervate droplets are capable of sequestering reagents and enzymes with a long retention time, and demonstrate multistep cascading reactions through the liquid-liquid interfaces. The ability to change phase dynamics is also demonstrated through salt-mediated dissolution of coacervate droplets, which leads to the release and mixing of separately sequestered reagents and enzymes. Finally, as phase-separated materials in membraneless organelles are often substrates and substrate analogues for the enzymes sequestered or excluded in the organelles, this paper explores the interaction between DEX and dextranase, an enzyme that hydrolyzes DEX. The results reveal that dextranase suffers from substrate inhibition when partitioned directly in a DEX phase but that this inhibition can be mitigated and reactions greatly accelerated by compartmentalization of dextranase inside a coacervate droplet that is adjacent to, but phase-separated from, the DEX phase. The insight that compartmentalization of enzymes can accelerate reactions by mitigating substrate inhibition is particularly novel and is an example where artificial membraneless organelle-like systems may provide new insights into physiological cell functions.