How Did Antarctic Octopuses Thrive in Subzero Seas? Blue Blood and Cold-Adapted Enzymes Unveiled

Antarctic octopuses face the challenge of surviving in the world's coldest waters, with temperatures ranging from -2°C to 10°C. To understand their adaptation to such extreme cold, researchers from the Marine Biological Laboratory (MBL) conducted a study on these octopuses living in the Southern Ocean.

They focused on an essential nervous system enzyme, the sodium-potassium pump, and analyzed its adaptations. The research described in Proceedings of the National Academy of Sciences sheds light on how life in this frigid environment has led to specific genetic changes in these creatures, revealing their remarkable ability to thrive in the extreme cold.

Living in the World's Coldest Waters

Temperature is crucial for life as enzymes that drive biochemical reactions in the body rely on thermal energy or heat to function. As temperatures drop, enzyme activity decreases and eventually stops.

Antarctic waters support diverse marine life due in part to the presence of dissolved oxygen, compensating for reduced oxygen transport caused by thicker blood and lower tissue diffusion. Some species, like Antarctic icefish, do not rely on hemoglobin for oxygen transport, distinguishing them as the only vertebrates to do so.

However, the specific mechanisms that blue-blooded octopuses use to sustain oxygen supply in the extreme cold remain less understood.

Octopuses lack the ability to regulate their body temperature, yet they thrive in the frigid waters of Antarctica, where the cold significantly slows down their enzymatic reactions, particularly affecting their nervous system.

While researchers have extensively studied cold adaptation in many proteins, they have often overlooked membrane proteins embedded in the cell's outer layer. Membrane proteins, such as the Na+/K+-ATPase, play essential roles in transporting ions into and out of cells, creating electrical potential differences used by neurons for communication.

How Antarctic Octopuses Survive in Cold Water

A team of researchers from the Marine Biological Laboratory, the University of Puerto Rico, and the US National Institute of Neurological Disorders and Stroke investigateed enzyme adaptation in octopuses.

Researchers developed two models: one based on the sodium-potassium pump enzyme from Antarctic octopuses (Pareledone) and the other from a temperate species, the two-spot octopus (Octopus bimaculatus).

They focused on the sodium-potassium pump enzyme due to its critical role in exporting sodium ions and importing potassium ions while using ATP as an energy source, which is vital for cell functions and solute transport across various temperature conditions.

The research confirmed that the Antarctic enzyme outperformed its temperate counterpart, maintaining efficient functionality even at extremely cold temperatures like -1.8°C.

Through systematic mutation testing, the scientists pinpointed three key mutations, mostly located at the interface between the enzyme and the cell membrane, with the L314V mutation being the most vital, as the enzyme ceased to function at near-freezing temperatures without it.

While the precise mechanisms behind this specific mutation require further investigation, biophysicist Miguel Holmgren from the US National Institute of Neurological Disorders and Stroke found the adaptations at the interface between the protein and the membrane to be both logical and anticipated.

In their future research, the team aims to conduct additional experiments to unravel the intricate mechanisms by which the protein pumps in Antarctic octopuses enable cells to remain active and functional in the harsh cold of their environment.