Are Globular Proteins Soluble? (Explained for Beginners)

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Globular proteins also called spheroproteins are spherical, having a “globe-like” structure. They are one of the most commonly found protein types. Let us look into it.

Globular proteins are usually soluble in water. They form colloids in the water. The word “globin” specifically refers to those proteins having the globin fold. As they are volatile, globular proteins need extremely ideal circumstances to work effectively.

Since a wide variety of architectural configurations can fold into an approximately spherical shape, globular proteins can be classified into a number of fold classes. Other kind of proteins present are disordered, filamentous and membrane proteins. Unlike the globular proteins, these type of proteins does not form colloids in water. Let us discuss the other facts.

Are globular proteins soluble in water?

The proteins that are mostly spherical, have a spherical shape, and are easily soluble in water are defined as the globular proteins. Let us see if they are soluble.

Majority of globular proteins are water soluble. They consist of irregular amino acid sequence. The weak intermolecular force helps them to get soluble in the liquids easily. They have a circular shape of three dimensions due to polypeptide chains that are folded together to give spherical shape.

Water solubility is advantageous to the globular proteins. Due to this feature, they can easily get transported to their action area by getting dissolved in blood or any other fluids in the body. These proteins also have the capability to get dissolved in different acids and bases.

Why globular proteins are soluble?

Globular proteins have the capability of getting dissolve in liquids due to the amino acids that have a unique structural arrangement. Let us discuss the reason of this.

Globular proteins are soluble due to hydrophilic amino acids present on their surface. Hydrophobic amino acids are found deep within for interactions taking place along side chains between the hydrophobic groups of amino acids. This fundamental property of globular proteins makes them water soluble.

A hydrogen atom is covalently bonded to an atom that is extremely electronegative in nature, like N, O, or F, so that they can form a non-covalent connection known as a hydrogen bond. Proteins’ solubility in a liquid medium is mostly due to the hydrogen bonds that exist between the polar groups on the surfaces of proteins and the solvent molecules.

Are globular proteins hydrophobic in nature?

The hydrophobic groups are crammed together to create hydrophobic clusters in the folds, while the hydrophilic groups are found on top. Let us figure it out.

Globular proteins are hydrophobic in nature as they have a hydrophobic core that is encircled by a hydrophilic coat outside the surface that engages with water. Unfolding takes place, causing the protein to become a mess. But in this process, the fundamental structure of a protein is kept intact.

Hemoglobin
Image Credit: Hemoglobin- Wikimedia

The polypeptide’s tertiary fold is defined as the polar residues that are left exposed while the side chains with polar side chains are hidden deep inside the center. Myoglobin, insulin, transferrin, and hemoglobin are some of the best examples known for globular proteins that contains this type of groups showing hydrophobic feature.

What interactions take place?

As explained above, about the positions of the hydrophobic and hydrophilic amino acids in the globular proteins, the interactions are quite unique.

Interactions between hydrophobic and hydrophilic groups occur. The nonpolar residues released from water creates an interior molecular where they are deposited or hidden. This kind of effect is known as the hydrophobic effect that is expected to have a significant part in facilitating this process.

Proteins’ enhanced solubility is the result caused by the interactions between the water molecules of polar groups and surface-attached polar groups. Their functions in human body may include transportation of oxygen in blood, metabolism of glucose, storage of oxygen in muscles, acts as catalyst in different reactions in body.

Why globular proteins are hydrophobic?

The Transmembrane helices are predominantly hydrophobic with specific distribution of positively charged residues. Let us discuss the reason behind hydrophobic property.

The hydrophobic effect of is due to the aggregation and burial of the hydrophobic surface decreases the amount of unwanted interactions of these groups with water. This is widely believed to be the major driving force behind the folding of the polypeptide chain into the compact globular shape.

225 Peptide Bond 01
Image Credit: Peptide bonds- Wikimedia

Trans Membrane Hidden Markov Model (TMHMM) is a bioinformatics tool which is used on Hidden Markov Model (HMM) that performs the above function. During the process of biosynthesis, a tight particle with an inner core which is protected from the surrounding solvent forms when the folds are seen within the globular proteins.

Solubility characteristics of globular proteins

Below we are going to discuss some of the crucial globular proteins’ distinguishing solubility characteristics:

1. Shape

Tertiary structures are created when amino acid chains fold over one another. The aforementioned note makes clear that globular proteins have a ball-like spherical form. Proteins are rounded, spherical in shape which is made possible by the tightly packed arrangement of amino acids within a molecule.

2. Dissolubility

The way how the amino acids are arranged in their structural composition, globular proteins are very soluble in liquid medium like water, acids and bases. Proteins’ enhanced solubility is caused by the interactions between the polar water molecules and the polar groups attached to the surface.

3. Amino Acid Sequence

Amino acid sequence of globular proteins is generally unpredictable. These proteins’ polypeptide chains contain amino acids that don’t repeat every few amino acids at regular intervals. It is contrary to fibrous proteins, that contain a sequence of amino acid that is extremely repetitive in nature.

4. Stability

They are very unstable due to the structural composition, globular proteins are more susceptible to have even small modifications in pH or temperature. The reason is lack of particularly strong connections between the side chains of amino acids.

5. Denaturation

Proteins can lose their secondary and tertiary structures by a process called denaturation, but their peptide linkages are left unbroken. Heat, pH, acids, bases, detergents, heavy metals, and other denaturing agents are only a few examples of the many denaturing agents that can be used.

Sometimes, the denaturation process may be undone, and the protein may refold into its native tertiary globular form. The majority of time, when the denaturing agent has been removed, denatured proteins are unable to regain their original structure. They develop a persistent state of imbalance. Such denatured proteins precipitate without dissolving in water.

Conclusion

The chemicals found in living things in the greatest abundance are proteins. Proteins do almost all of the tasks that cells need to do. In the bodies of living things, they perform both the functional and structural roles.

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