(ORDO NEWS) — The ability of crocodile hemoglobin to bind and retain oxygen is determined not by phosphates, as in most vertebrates, but by bicarbonates.
This allows these reptiles to make optimal use of oxygen and stay submerged for long periods of time.
To find out how such a protein appeared, scientists reconstructed the hemoglobin of modern and ancient crocodiles, as well as archosaurs.
It turned out that its effect is provided not by individual mutations, but by their complex combinations.
The success of the crocodile as a top predator lies in its ability to stay under water for a long time, guarding its prey.
This ability is provided by the unique structure of the protein hemoglobin, which delivers oxygen from his lungs to the tissues at a slow but constant rate.
The uniqueness of crocodile hemoglobin led scientists to wonder why, of all vertebrates, only these reptiles got such a protein.
To answer this question, researchers from the University of Nebraska at Lincoln (USA) recreated the hemoglobin of archosaurus, the last known common ancestor of birds and crocodiles, which lived 240 million years ago, as well as the common ancestor of modern crocodiles 80 million years old.
It turned out that such a unique hemoglobin appeared only in crocodiles. Moreover, instead of several key amino acid substitutions, its properties are provided by 21 complexly interconnected mutations.
In most vertebrates, the ability of hemoglobin to capture and retain oxygen is determined by molecules known as organic phosphates. It is they who, by joining hemoglobin, make it release oxygen.
However, in crocodiles and alligators, the role of phosphates is played by bicarbonates, which are formed during the breakdown of carbon dioxide.
Since the tissues in the process of life produce a lot of carbon dioxide, bicarbonate is also formed.
Its quantity determines how oxygen is distributed throughout the body and ensures that it reaches the tissues that need it most.
Comparison of the hemoglobins of an archosaur and an ancient crocodile revealed changes in the amino acid composition of proteins.
To test which ones mattered most, the scientists added certain crocodile-specific mutations to archosaurus hemoglobin and evaluated its function.
Contrary to conventional wisdom, evolutionary changes in the hemoglobin response to bicarbonates and phosphates appeared to be caused by different sets of mutations, so that the gain in one mechanism was independent of the loss of the other.
Although a few amino acid changes were sufficient to eliminate the phosphate binding site, many other changes were needed to completely eliminate hemoglobin phosphate sensitivity.
In much the same way, two mutations seem to directly cause bicarbonate sensitivity, but only other protein changes have allowed crocodilian hemoglobin to become so effective.
Contact us: [email protected]