Myoglobin: what is myoglobin, characteristics and function of this protein?

Let's see what is myoglobin, a heteroprotein important for the functioning of the human body.

The world of human biochemistry, in all its meanings, explains the metabolic processes that occur within us. Beyond ethereal concepts and self-identities, we must recognize that the human being is nothing more than a set of chemical pathways, electrical impulses, cellular respirations and polypeptide chains, at least on a purely physiological level.

Therefore, thousands of small molecules account for thousands of small molecules, thousands of small molecules explain our behaviors, habits, and ailments.. Gastric enzymes are responsible for digestion in the stomach, hemoglobin in red Blood cells enables the transmission of oxygen to our tissues, and the release of synaptic complexes between neurons enables us to think, no more and no less. Simply put: we are the biomolecules that we synthesize, however small or insignificant they may seem.

Among the whole biological conglomerate that is the human body, there are a number of proteins or conjugates responsible for very specific functions, which often escape general attention because of the specific language they entail. Here we will see what is myoglobin, a muscle heteroprotein that has many similarities with classical hemoglobin..

What is myoglobin?

Myoglobin is a heteroprotein, i.e. it is composed of a protein part (apoprotein, amino acids linked by peptide bonds) and a smaller non-protein part (the prosthetic group).the prosthetic group. The key distinguishing feature between a protein (holoprotein) and a heteroprotein is that the latter has lipids, carbohydrates, nucleic acids and even metals in its three-dimensional structure.

To further refine the thread, we can point out that myoglobin is a chromium-type heteroprotein. a heteroprotein of the chromoprotein type, since it has a metal in its chemical compositionwhich gives it a characteristic staining. Myoglobin is composed of a polypeptide section of 153 amino acids and a heme group containing an iron atom, just like hemoglobin. Because of this "heme" group, we can state that the main function of myoglobin is to store oxygen.

In addition, it is worth noting that myoglobin is composed of a single polypeptide chain consisting of 8 alpha-helices (secondary structure of the amino acid conformation), which is associated with an oxygen insertion site. In the center, an iron-containing porphyrin ring is present. A proximal histidine group (His-93) is directly associated with the iron molecule, while a distal histidine group (His-64) is placed on the opposite side of the formation.

In contrast, hemoglobin (responsible for transporting oxygen in blood, within red blood cells) is composed of four different polypeptides and four different oxygen binding sites, allowing for diverse binding kinetic properties. It could be said that, from a chemical point of view, it is more "complex" than myoglobin..

If we want to give you an idea of this whole conglomerate, it is the following: myoglobin consists of only one amino acid chain (polypeptide), which in turn is in the form of 8 connected alpha helices, arranged in a coiled form over the three-dimensional conformation. At the center of the heteroprotein is a heme group, with an iron molecule. If we could unwind its tertiary structure, we would see a string of 8 subunits attached to a heme ring.

Function of myoglobin

Like hemoglobin, myoglobin is a cytoplasmic heteroprotein that enables the binding of oxygen to a heme group.. However, having four polypeptide chains (globin), hemoglobin has four heme groups, which allows it to bind more oxygen to its tertiary structure. Thus, hemoglobin has more "oxygen cargo", whereas myoglobin has a higher affinity for oxygen, but a lower amount (only one heme group/one O2 molecule). These differences are in conjunction with the functionality of each molecule: hemoglobin transports, whereas myoglobin stores.

At this point, it should be noted that myoglobin concentrations are highest in the striated musculature of vertebrates, specifically in the cytoplasm of cardiomyocytes and in the sarcoplasm of muscle fibers.specifically, in the cytoplasm of cardiomyocytes and in the sarcoplasm of muscle fibers. Based on this premise, it can be assumed that the main function of myoglobin is to provide oxygen to muscle mitochondria when the organism is under stress, in order to avoid hypoxia at tissue level.

In other words, myoglobin serves as a buffer for intracellular oxygen concentration and also as an O2 reserve at the muscular level. This concept is confirmed by a reality that is as curious as it is expected: animals that live in water and spend long periods of time submerged have 30 times more myoglobin in their cellular environment compared to those that have oxygen available at all times.

These are some more functions of myoglobin, contextualized in the organism's environment:

• It facilitates oxygen diffusion: this heteroprotein desaturates at the onset of muscle activity, which increases the oxygen diffusion gradient from the capillaries to the cytoplasm.
• It appears to have enzymatic functions: it is required for the active breakdown of nitric oxide to nitrate. Nitric oxide metabolism promotes mitochondrial activity.
• Helps to eliminate reactive oxygen species (ROS): ROS are very small molecules derived from normal cellular metabolism, but they can damage the cell and cause aging. Therefore, myoglobin helps to keep their concentrations to a minimum.

As you can see, the functionality of myoglobin lies not only in the storage of an O2 molecule thanks to its heme group, but also in its ability to store O2.. Although this is its main task, it also has other equally important roles for the well-being of the cellular environment.

The role of myoglobin in clinical pictures

Myoglobin is encoded by the MB gene in humans, and like any ordered DNA sequence, it is susceptible to mutations. Dysfunctionality of the MB gene has been associated with various conditions, such as compartment syndrome or medulloblastoma.

In addition, experimental models (knockout mice) with mutated myoglobin develop lethal cardiac disease during fetal development. The few models that survive these conditions express compensatory mechanisms, but survival is low. Therefore, it is claimed that myoglobin is essential for the functioning of the body. is essential for the functioning of the body.

Beyond conjectural grounds, myoglobin has been directly associated with a widely known clinical entity: rhabdomyolysis. In this severe condition, damage to the myocyte (muscle cell) membrane occurs, resulting in abnormal calcium accumulation within the muscle. This results in muscle lysis and necrosis, which in turn increases the blood concentration of molecules that should not be there.

Interestingly, myoglobin is the protein that causes the most damage in muscle. is the protein that causes the most damage to the kidneys when it infiltrates the circulatory system and ends up being "filtered" in the renal environment.. It is believed that this heteroprotein can precipitate in the kidney tubules, accumulating and causing obstructions. This mechanism of toxicity explains, in part, why renal failure is one of the main side effects of rhabdomyolysis.

Finally, it should be noted that the presence of myoglobin in the urine is measured to detect this condition, since a concentration of 100 mg/dl is capable of changing the color of pee.

Summary

When we pay attention to a protein, enzyme or molecule related to metabolism, it is a serious mistake to focus only on its main structure and function. Yes, myoglobin stores oxygen to prevent muscle hypoxia, but it also has enzymatic activity, neutralizes reactive oxygen species, facilitates O2 diffusion in the cellular environment and serves as one of the diagnostic criteria for rhabdomyolysis (either in its plasma or urine concentration).

After all, every biomolecule has more than one function in our body, and if we believe that it only performs one function, it is probably because we have not discovered the rest.