Dense liquid droplets act as cellular computers
An emerging field explores how groups of molecules condense together inside cells, the way oil droplets assemble and separate from water in a vinaigrette.
In human cells, “liquid-liquid phase separation” occurs because similar, large molecules glom together into dense droplets separated from the more diluted parts of the fluid cell interior. Past work had suggested that evolution harnessed the natural formation of these “condensates” to organize cells, providing, for instance, isolated spaces for the building of cellular machines.
Furthermore, abnormal, condensed — also called “tangled” — groups of molecules in droplets are nearly always present in the cells of patients with neurodegenerative conditions, including Alzheimer’s disease. While no one knows why such condensates form, one new theory argues that the biophysical properties of cell interiors change as people age — driven in part by “molecular crowding” that packs more molecules into the same spaces to affect phase separation.
Researchers compare condensates to microprocessors, computers built into circuits, because both recognize and calculate responses based on incoming information. Despite the suspected impact of physical changes on liquid processors, the field has struggled to clarify the mechanisms connecting phase separation, condensate formation, and computation based on chemical signals, which occur at much smaller scale, researchers say. This is because natural condensates have so many functions that experiments struggle to delineate them.
To address this challenge, researchers at NYU Grossman School of Medicine and the German Center for Neurodegenerative Diseases built an artificial system that revealed how the formation of condensates changes the action at the molecular level of enzymes called kinases, an example of chemical computation. Kinases are protein switches that influence cellular processes by phosphorylating — attaching a molecule called a phosphate group — to target molecules.
The new analysis, published online September 14 in Molecular Cell, found that the formation of engineered condensates during phase separation offered more “sticky” regions where medically important kinases and their targets could interact and trigger phosphorylation signals. More