Waters near the Antarctic contain high levels of dissolved salt and can remain just above, or even below, freezing points. However, certain organisms, like Antarctic octopus species, have evolved to thrive in these challenging conditions. This cold environment would be fatal to species accustomed to the warmer climes of the north. However, nature has a way of adapting to extremities.
The experts examined how extreme cold had influenced a pivotal enzyme in the octopus’s nervous system, offering new insights into the vast array of adaptations that enable life in extreme settings.
“We looked in real detail at a very important enzyme for the nervous system, the sodium-potassium pump, and we asked, ‘Where do we see most of these sites of adaptation?,’” said Joshua Rosenthal, a senior scientist at MBL.
For all living organisms, temperature plays a significant role since enzymes, which initiate myriad biochemical reactions, rely on thermal energy or heat. As temperatures drop, enzyme activity diminishes, coming to an eventual standstill.
Unlike some animals, such as humans, that can generate heat internally, octopuses lack this capability.
Yet, these marine creatures have managed to exist in Antarctic waters, where the cold reduced the rate of their enzymatic reactions up to 30-fold. This poses a challenge for their nervous systems, which depend on a series of well-synchronized reactions.
“When you slow them all down to such a degree, it’s a big question: How do they adapt?” Rosenthal pondered.
While scientists have previously explored cold adaptation in numerous proteins, they often overlooked those embedded in cellular membranes.
These proteins are crucial for tasks like ion transport within cells. The focal protein of this study, the Na+/K+-ATPase, plays a role in maintaining electrical gradients essential for neuron communication.
In past studies, Rosenthal, alongside Miguel Holmgren from the U.S. National Institute of Neurological Disorders and Stroke and a summer Whitman investigator at MBL, discovered that the sodium-potassium pumps of an Antarctic octopus (genus Pareledone) were less hindered by cold compared to those of the two-spot octopuses (Octopus bimaculatus) living in temperate regions, such as near California.
The researchers compared the amino acid composition of the two pumps to identify differences. They pinpointed specific amino acid variations, assessing their significance by exchanging them between pumps. This exchange revealed three pivotal variations enabling the pump to function efficiently in nearly freezing conditions.
One specific variation, termed L314V, emerged as particularly crucial. Modifying this amino acid could eliminate the pump’s cold-resilient nature.
Upon examining these variations within the pump’s structure, the scientists found them located at the protein’s edge, adjacent to the lipid-rich membrane. For instance, the L314V variation might optimize the pump’s movement against the membrane, thus enhancing its efficiency.
“It makes sense to us” that the interface between the protein and the membrane would be a site for such adaptations, Holmgren explained. “Once we have studied more membrane proteins, I think we will see more examples of this.”
The study is published in the journal Proceedings of the National Academy of Sciences.
Image Credit: Tom Kleindinst/Marine Biological Laboratory
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.