“They are investigating an area that is largely unexplored,” he said. Sol Grunerwho researches molecular biophysics at Cornell University; was consulted for the study but was not a co-author.
Plasmallogenic lipids are also found in the human brain and their role in deep-sea membranes could help explain aspects of cell signaling. More immediately, the research reveals a new way in which life has adapted to the most extreme conditions of the deep ocean.
Crazy on the membrane
The cells of all life on Earth are surrounded by fatty molecules known as lipids. If you put some lipids in a test tube and add water, they automatically line up back to back: the water-hating fatty tails of the lipids mix together to form an inner layer, and their water-loving heads move together. They organize together to form the outer layer. portions of a thin membrane. “It’s like the oil and water are separated in a dish,” Winnikoff said. “It’s universal for lipids and it’s what makes them work.”
For a cell, an outer lipid membrane serves as a physical barrier that, like the outer wall of a house, provides structure and keeps the inside of the cell inside. But the barrier can’t be too strong: It’s packed with proteins, which need some wiggle room to carry out their various cellular functions, such as transporting molecules across the membrane. And sometimes a cell membrane is pinched to release chemicals into the environment and then fuses again.
Therefore, for a membrane to be healthy and functional, it must be robust, fluid and dynamic at the same time. “The membranes are balancing right on the edge of stability,” Winnikoff said. “Even though it has this really well-defined structure, all the individual molecules that make up the sheets on either side flow around each other all the time. In reality, it is a liquid crystal.”
One of the emerging properties of this structure, he said, is that the middle part of the membrane is very sensitive to both temperature and pressure, much more so than other biological molecules such as proteins, DNA or RNA. If you cool a lipid membrane, for example, the molecules move more slowly, “and eventually they’ll just stick together,” Winnikoff said, like when you put olive oil in the refrigerator. “Biologically, that’s generally a bad thing.” Metabolic processes stop; The membrane may even crack and leak its contents.
To avoid this, many cold-adapted animals have membranes composed of a mixture of lipid molecules with slightly different structures to keep the liquid crystal flowing, even at low temperatures. Since high pressure also slows the flow of a membrane, many biologists assumed that deep-sea membranes were constructed in the same way.
