4.15
Structural Protein Function
Structural proteins are a category of proteins responsible for functions ranging from cell shape and movement to providing support to major structures…
Structural proteins are a class of proteins that support cell shape and movement. Outside of the cell, these proteins are present in structural body parts, such as bones, cartilage, and skin.
Collagen, the most abundant protein in mammals, is a structural protein found throughout the body in the extracellular matrix.
This protein winds into a triple helix that polymerizes into elongated fibrils, which then further assemble into larger fibers. Among its many structural functions, it contributes to cell and tissue shape.
The cytoskeleton is predominantly composed of structural proteins and forms the basic framework of a cell. It contains three main types of filaments: microfilaments, intermediate filaments, and microtubules.
Actin is a structural protein that makes up the microfilaments. This protein self-polymerizes into filaments and contributes to cell shape, organization, movement, and division.
Intermediate filaments can be composed of different proteins depending on the cell type. For example, keratin intermediate filaments are found in epithelial cells, whereas peripherin intermediate filaments are found in the peripheral neurons. The primary structural function of these filaments is to reinforce cells and organize them into tissues.
The microtubules consist of a class of structural proteins called tubulins. Tubulins self-assemble to form microtubules that contribute to the organization of the cytoplasm including the location of the organelles.
Structural proteins are necessary for the health of an organism, and mutations in the genes that code for these proteins can result in various diseases, including skeletal and cardiovascular abnormalities.
View the full transcript and gain access to JoVE Core videos
Q1: What is collagen and where is it found in the body?
Collagen is the most abundant protein in mammals and serves as a primary structural protein throughout the body. It is found in the extracellular matrix and in connective tissues such as skin, ligaments, and tendons, where it provides tensile strength and elasticity. In bones and teeth, collagen mineralizes to form hard tissues and contributes to their load-bearing capacity.
Q2: How does collagen assemble into its functional structure?
Collagen winds into a triple helix structure that polymerizes into elongated fibrils. These fibrils further assemble into larger fibers, creating a hierarchical structure. This assembly process enables collagen to contribute to cell and tissue shape while providing structural support throughout the body.
Q3: What are the three main types of filaments in the cytoskeleton?
The cytoskeleton contains three main types of filaments: microfilaments, intermediate filaments, and microtubules. Microfilaments are composed of actin and contribute to cell shape, organization, movement, and division. Intermediate filaments reinforce cells and organize them into tissues, while microtubules organize the cytoplasm and the location of organelles.
Q4: How do actin filaments contribute to cell function?
Actin is a structural protein that self-polymerizes into microfilaments. These actin filaments contribute to cell shape and organization and can enable cell movement and division when acting in conjunction with myosin. Actin filaments form the basic framework of the cell cytoskeleton and support dynamic cellular processes.
Q5: What determines the composition of intermediate filaments?
The composition of intermediate filaments varies based on cell type, with around 70 different genes coding for various intermediate filaments. Epithelial cells contain keratin intermediate filaments, peripheral neurons contain peripherin, and muscle cells contain desmin. This variation allows intermediate filaments to meet the specific structural needs of different cell types.
Q6: What role do tubulins play in the cell?
Tubulins are structural proteins that self-assemble to form microtubules. These microtubules contribute to the organization of the cytoplasm, including the location of organelles. Microtubules are also essential for mitosis and cell division, making them critical for maintaining proper cellular organization and enabling successful cell division.
Q7: What diseases can result from mutations in structural protein genes?
Mutations in genes coding for structural proteins can cause severe diseases. A mutation in a collagen gene can result in osteogenesis imperfecta, characterized by weak bones and connective tissue deformities. Different collagen mutations can cause Alport syndrome, affecting organs such as kidneys, eyes, and ears.