fibrous proteins

• Proteins can be classified into fibrous proteins and globular proteins.
• Fibrous proteins support cell shape, have protective roles, provide mechanical properties, regulate cellular processes, exhibit catalytic activity, and participate in transport.
• Globular proteins have similar functions to fibrous proteins but are soluble in water and can be digested.
• Fibrous proteins include scleroproteins which are not soluble in water, can't be digested, are thermostable, and have mechanical strength.
• Fibrous proteins also include keratin, collagen, elastin, and silk fibroin.
• Keratin is found in the epidermis, is ectodermal, and has anti-parallel alignment of 2 superhelix structures that form a tetramer.
• Elastin has a single genetic type, random coils for elasticity, no structured repeats, hydroxylysine is absent, carbohydrate modification is absent, and desmosin and Lysine-Norleucine cross-links.
• Cross-links in Elastin are formed by Desmosine and Lysine-Norleucine.
• Silk Fibroin has many weak bonds that give it stability (Hydrogen and van der Waals).
• Silk Fibroin has a β-pleated sheet structure, nearly half of the amino acids are Glycine, R groups of Alanine and Serine place opposite of R group of Glycine, and it is the most elongated form of β-pleated sheet structure.
• Collagen has different genetic types, a triple-helix structure, (Gly-X-Y)n repeats, hydroxylysine is present, carbohydrate modification is present, and aldol cross-links.
• The helical chain of keratin is rich for hydrogen bonds and between two helixes, the structure is rich for disulfide bonds.
• Keratin is rich for hydrophobic amino acids such as alanine, valine, leucine, isoleucine, methionine, and phenylalanine.
• Physical properties of collagen vary depending on the tissue it is found in: skin, veins - Elasticity; bones, teeth - Hardness; tendons, ligaments - Pulling power.
• Collagen constitutes ~30% of total protein and 6% of body weight.
• Cysteine is low in skin keratin.
• As the cysteine ratio increases, the hardness of keratin increases.
• Collagen types are clinically relevant in diseases such as scurvy, which is caused by hydroxyproline deficiency and failure to form Tropocollagen cross-bonds, leading to delayed wound healing and capillary fragility.
• Four protofibrils make a microfilament.
• Collagen is stabilised by hydrogen bonds.
• Three α-chains come together to form a right-handed superhelix.
• Elastin does not contain any hydroxylysine.
• Two protofilaments side by side make a protofibril.
• In the process of collagen hydroxylation, molecular oxygen is introduced to amino acids side chains (proline and lysine), vitamin C and Fe2+ are cofactors, and these added –OH groups help to make more hydrogen bonds to stabilise the structure.
• A single collagen chain is a left-handed chain (3 amino acids in every turn).
• Collagen has a triple-helix structure.
• Disulfide bonds give insolubility property.
• Ehlers-Danlos Syndromes Type III is a collagen defect caused by gene anomaly, resulting in dislocated joints, musculoskeletal deformities, skin anomalies, and artery and uterine ruptures.
• Collagen has various functions and roles, including providing structure, support, and protection for the body.
• Elastin provides the ductility and flexibility of the skin, blood vessels, and lungs, and is a hydrophobic protein, 800 amino acids long, rich in glycine, alanine, and lysine, but poor in proline, and contains small amounts of hydroxyproline.
• Osteogenesis imperfecta is a type of collagen synthesis deficiency, resulting in bone deformities and breaks.
• Collagen has covalent cross-links that stabilise the structure.
• Collagen is rich for Proline and Hydroxyproline.
• Keratin is formed by the anti-parallel alignment of two superhelix structures, forming a tetramer.
• No tryptophane or cysteine can be found in collagen structure.
• Tetramers line up end to end to form protofilaments.
• The cysteine content in the hair structure is around 14%.
• There are 28 types of collagen in the human body.