Most biochemical research has historically focused on the obvious cogs of machines that keep life moving. Protein folding, genetic activity and electrical signaling pathways are the easiest targets for finding irregularities that lead to disease.
However, recent research has pointed to another type of cell structure that may play an equally important role. Called biological condensates, these structures exist due to differences in density, like oil droplets floating in water, and form compartments within cells without the need for the physical boundary of a membrane.
Previous studies have shown that these blobs can separate or hold together certain proteins and molecules, hindering or promoting their activity. They also revealed that these structures provide an alternative energy source that could power some aspects of biological chemistry.
However, these results focused on the effects created in the immediate vicinity of the condensates themselves. Researchers had not yet identified ways in which they might influence biochemistry, far from their physical structures.
Now, in a new study published September 10 in the journal CellResearchers from Duke University and Washington University in St. Louis have shown that the formation of biological condensates affects cellular activity far beyond their immediate environment. The results show that they may represent a previously missing mechanism by which cells modulate their internal electrochemistry. And those internal controls in turn influence the cell membrane, allowing these modest blobs to influence global traits and outcomes like antibiotic resistance.
“Our research shows that condensates influence cells far beyond direct physical contact, almost as if they have a wireless connection to how cells interact with the environment,” said Lingchong You, the James L. Meriam Distinguished Professor of Biomedical Engineering at Duke. “In addition to demonstrating the electrical mechanisms behind this connection, we proved that condensate formation can make cells more tolerant to certain types of antibiotics and more sensitive to others.”
“This is probably just the tip of the iceberg,” added Ashutosh Chilkoti, the Alan L. Kaganov Distinguished Professor of Biomedical Engineering at Duke. “We expect these electrical potential effects to manifest themselves in a wide variety of ways through cellular behavior.”
Condensates act like a sponge, sucking in various proteins, enzymes, ions and other biomolecules as they form, while excluding others. And if they trap enough ions in their compartment to become positively or negatively charged, that imbalance should be reflected in the cellular environment around them.
This electrostatic activity provides a handle for the formation of biological condensates that influence the electrical potential of the cell membrane and the electrochemical environment in the cell. And because these environmental cues are crucial to many biological processes, it provides a mechanism by which these humble blobs can directly influence the way cells interact with the world around them.
“Even a small number of these condensates distributed centrally, far away from the cell membrane, can trigger a chain reaction that can change this global property,” explains Yifan Dai, assistant professor of biomedical engineering and member of the Center for Biomolecular Condensates in Washington. University in St. Louis, who conducted the study as a postdoctoral fellow at Duke. “This paper shows that there is no escape from these effects. As long as these little blobs form, many things are affected, even gene regulation on a global scale. When I saw that, it was quite shocking to me.”
To prove this point, the researchers attempted to show that this phenomenon could affect how well bacteria survive interactions with certain antibiotics. The researchers created colonies of E.coli bacteria to form internal condensates, either by properly stressing them or by manipulating the gene expression of the condensate-forming proteins. They then tested the resulting electrical charge in their cell membranes and exposed them to antibiotics.
The results showed that condensate formation caused some cell membranes to become more negatively charged, which directly affected whether or not the cells responded to the antibiotics, as they are also charged particles. But this is just the beginning of this line of research, the researchers say, because many biochemical processes depend on the electrical potential present in the cell membrane.
“Our work reveals a role of condensates in regulating global cellular physiology,” You said. “Although we do not yet have a concrete mechanistic understanding of how cells deploy this activity to regulate their functionality, it is an important discovery that this happens at all.”
This work was supported by the Air Force Office of Scientific Research (FA9550-20-1-0241) and the National Institutes of Health (R35-GM127042)
