Active enzymes set crowded molecular droplets in motion
Experiments and simulations found a two-way relationship between enzymes and protein-rich droplets used to model crowded cellular environments. Droplet composition changed catalytic efficiency, while active enzymes increased molecular mobility and generated mixing flows. The simplified laboratory system connects chemical reactions with physical motion, with the extent of the effect in living cells still to be established.
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Crowding changed the efficiency of enzyme reactions
An experimental and theoretical study in Nature Communications examined how enzymes interact with dense molecular droplets. Researchers at Japan's Okinawa Institute of Science and Technology and RIKEN research institute worked with Germany's Max Planck Institute for Dynamics and Self-Organization. Their simplified laboratory system represents crowded cellular environments, where membrane-free compartments concentrate molecules and provide surroundings for biochemical reactions.[1], [2]
Droplets rich in the protein bovine serum albumin provided the model environment. The team studied lactate dehydrogenase and alcohol dehydrogenase, enzymes involved in metabolic reactions. Being inside a droplet increased catalytic efficiency relative to dilute solution. Raising the protein concentration further within the droplet, however, reduced that efficiency. The outcome depended on how crowded the surrounding environment became.[1]
Active enzymes increased movement around them
Atomistic simulations suggest that crowding favours a closed enzyme shape that facilitates a reaction, while stronger crowding slows the movement of reacting molecules. The enzyme's surroundings therefore influence both its configuration and the transport involved in catalysis. The researchers combined experiments, simulations and theory to examine effects stretching from protein interactions to the movement of molecules throughout a droplet.[1]
The influence also ran in the opposite direction. Proteins and tracer particles moved more readily in droplets containing active enzymes. Comparisons with inactive enzymes supported an explanation involving catalysis, rather than simply the presence of extra protein. The droplet's composition changed enzyme activity, and chemical activity in turn altered the physical mobility of the surrounding material.[1], [2]
Chemical gradients stir a simplified droplet
The researchers' theoretical model describes chemical concentration gradients producing small flows within and around a droplet. The institutional account reports that collaborating biochemists used tracer particles to confirm the flow's shape experimentally. This mixing connects molecular-scale reactions with the physical behaviour of the larger droplet, extending the investigation beyond changes to the enzyme's own activity.[1], [2]
The experiments used a simplified droplet rather than directly demonstrating the feedback inside living cells. A cell contains more chemical variety and structural complexity than this model system. The authors identify tests with other enzymes and crowding molecules as necessary to establish how general the effect is. The extent of this chemical and physical feedback in real cellular compartments remains an open research question.[1]
