Collagen and keratin are both different kinds of proteins found in the human body. Proteins are made up of smaller molecules known as amino acids. There are 20 kinds of amino acids which combine in different ways and quantities to form different proteins.
Amino acids are the monomers that when linked together through polypeptide bonds form a polymer known as a protein.
Collagen vs Keratin
The main difference between collagen and keratin lies in their constituents and their alignment. Both collagen and keratin are made up of different combinations of amino acids. While the polypeptide chains found in collagen are left-handed, the polypeptide chains in keratin are right-handed.
Collagen makes up our bones, cartilage, tendons and other connective tissues. Keratin, on the other hand, acts as a shield for our body and is found in the outermost layer of our skin, hair, nails, etc.
Comparison Table Between Collagen and Keratin
| Parameter of Comparison | Collagen | Keratin |
| Location Found | Extracellular matrix and connective tissue. | In epithelial cells and structures like hair, nails, etc. |
| Structural Constituents | Made up of hydroxyproline, glycine, proline and alanine. | Made up of phenylalanine, isoleucine, valine, methionine and alanine. |
| Types | There are 28 types of collagen proteins found in the human body. | There are two types of keratin found in the human body. |
| Effect on Epithelial Cells | Formation of collagen does not lead to the death of epithelial cells (cornification). | Formation of keratin gives rise of cornification of epithelial cells that makes the outermost layer of skin, hair and nails. |
| Commercial Use | Used in surgical reconstruction procedures. | Used in making cosmetics and as an additive in chemicals. |
What is Collagen?
Collagen is a fibrous protein present in the matrix outside the cell. It is considered as the most abundant protein in the animal kingdom. It provides strength and structure to our body. Almost 25% to 35% of all the protein content in our body is collagen.
Collagen is made in fibroblasts that are present in a large number inside the connective tissues.
When collagen mineralizes to be rigid, it forms the bone. When it mineralizes to be compliant, it forms the tendon and when it mineralizes to be a combination of both rigid and compliant, it forms the cartilage.
The molecules in collagen are in the form of long and thin fibrils. A single molecule of collagen is called tropocollagen. It is made up of three polypeptide chains that bind together to form a left-handed helix. Further, three of these left-handed helices combine to form a right-handed triple helix (also known as “superhelix”) that is stabilized by hydrogen bonds.
Collagen can be used for a wide number of reasons. It is used in cosmetic surgery, burn surgery and even to make casings for sausages! It can be used in foods as well as for medical purposes.
Lack of production of collagen causes a disease known as Ehlers-Danlos syndrome (EDS). Eating foods rich in vitamin C can increase the production of collagen in our body.
What is Keratin?
Keratin is also a fibrous protein. It is one of the main components in making our hair, skin and nails along with feathers, claws, hooves and horns in some other vertebrates. It protects our skin from stress or damage.
Keratin is made inside keratinocytes that are present in the dermis of the skin.
Keratin fibres supercoil to form a left-handed superhelix. Keratin has a special ability that helps in cornification of cells. When keratin production starts and the cell is filled with keratin, the cell organelles disappear and the cell undergoes death.
Cells present in the outermost layer of our skin contain keratin in their matrix which makes it waterproof. Keratin is used in making hair care products and other cosmetics.
Problems in keratin formation cause diseases like epidermolysis bullosa simplex (EBS) and epidermolytic hyperkeratosis (EH). Making eggs and onions as a part of your diet will help boost the formation of keratin in your body.
Main Differences Between Collagen and Keratin
- Collagen fibres mineralize to form our bones, tendons and other connective tissues while keratin fibres do not mineralize.
- Collagen is a right-handed superhelix and keratin is a left-handed superhelix.
- Collagen contains a rare amino acid known as hydroxyproline while keratin contains isoleucine.
- Collagen can be ingested but keratin cannot be ingested.
- Collagen is used for medical purposes while keratin is mostly used in cosmetics.
- Collagen is made in cells called fibroblasts. Keratinocytes present in the dermis of skin make keratin.
Conclusion
Collagen and Keratin are both an integral part of providing structure to our body. Both of them have properties like tensile strength and durability. Collagen is found in our connective tissues while keratin makes up nails, talons, horns, etc.
Collagen can be used to cover wounds as it helps in closing them and ultimately, healing them. The layer of keratinized tissue on our body is what protects our skin from wear and tear. Both proteins play a part in the healthy functioning of our body.
Although there may be some non-fibrillar collagens present, there are no non-fibrillar keratins present. Keratin production is the precursor of cornification (programmed death) of cells while collagen is involved in no such activity.
Lysinonorleucine is a residue that forms between the covalent bonds of lysine that remains in the polypeptide chain in collagen which adds to the cross-linking in the chains. In keratin, disulphide bonds between the polypeptide chains add to cross-linking.
Keeping aside their differences, collagen and keratin have a few similarities too. Both the proteins are highly insoluble in water and other organic solvents. In addition to that, they both are linear, fibrous proteins, have high tensile strength, have complex triple helical structures and are present in the extracellular matrix of cells.
References
- https://www.jstage.jst.go.jp/article/fstr/9/1/9_1_91/_article/-char/ja/
- https://www.sciencedirect.com/science/article/pii/S1010603001005846