Keratin filaments are a family of structural fibrous proteins that serve as fundamental building blocks in the human body. These specialized proteins contribute significantly to the physical integrity of various tissues. They are widely recognized for their ability to provide robust support and resilience to cells.
What Are Keratin Filaments?
Keratin filaments belong to intermediate filaments, a part of the cell’s cytoskeleton. These proteins have a fibrous, rope-like structure, which contributes to their strength. Their basic building blocks are protein subunits that assemble in a hierarchical manner.
The assembly process begins with individual keratin proteins, which are divided into two main types: Type I (acidic) and Type II (neutral-basic). A Type I keratin pairs with a Type II keratin to form a coiled-coil dimer. These dimers then associate in an anti-parallel and staggered fashion to create tetramers. Multiple tetramers combine laterally to form unit-length filaments, which elongate end-to-end to create mature keratin filaments.
Where Are Keratin Filaments Found?
Keratin filaments are found throughout the human body, particularly in tissues that experience mechanical stress. They are abundant in epithelial cells, which form the protective linings of organs, glands, and body surfaces.
The skin, hair, and nails are examples of structures where keratin filaments are concentrated, providing strength and rigidity. For instance, acidic keratins are found in the nail bed and the outermost layer of the skin (stratum corneum), while basic keratins are present in the deeper layers of the epidermis and hair follicles. Their presence in these locations helps these tissues withstand external forces and maintain their structural shape.
What Do Keratin Filaments Do?
The primary function of keratin filaments is to provide mechanical strength and structural integrity to cells and tissues. They form a resilient network within the cell’s cytoplasm, acting as a scaffold that helps cells resist stretching, compression, and other forms of physical stress. This internal support system is important for epithelial cells, which are exposed to mechanical forces.
Keratin filaments also play a role in cell-to-cell adhesion. They connect to specialized cell junctions called desmosomes, which firmly link neighboring cells. This connection creates a strong tissue architecture, allowing cells to act as a cohesive unit and maintain tissue integrity. Keratin filaments also shield cells from various forms of damage and aid in maintaining cellular shape and organization.
Keratin Filaments and Health
Dysfunctional or mutated keratin filaments can have significant implications for human health, leading to disorders characterized by fragile tissues. Genetic alterations in keratin genes can result in impaired filament formation or stability, compromising the mechanical resilience of cells and tissues.
One example is epidermolysis bullosa simplex (EBS), a group of genetic skin blistering disorders. In EBS, mutations in specific keratin genes, such as K5 and K14, lead to fragile skin that blisters easily from minor trauma. Hair abnormalities and brittle nails can also arise from defects in keratin filaments, highlighting their broad impact on the body’s protective barriers.