Recording-2025-03-18T19:29:57.144Z

Fibrous Proteins

• Definition: Fibrous proteins are structural proteins that provide support, protection, and shape to cells and tissues.

• Characteristics:

  • Composed of long, winding amino acid chains that form fibers.

  • Typically serve protective and supportive roles in organisms.

Structural Features of Fibrous Proteins

• Secondary Structures:

  • Usually feature long, helical structures (e.g., alpha helices) that are stabilized by hydrogen bonds.

  • Typically consist of a single secondary and tertiary structure due to their repetitive primary sequence.

  • Pseudo Repeat: Primary structure repeats every three amino acids (triple helix formation) due to the structure of the polypeptide (e.g., polyproline helix).

Keratin

• Primary Structure: Linear, characterized by a repetitive sequence of amino acids leading to fibrous formation.

• Composition:

  • Contains a pseudo repeat of seven amino acids where hydrophobic residues are located at positions one and four.

  • This arrangement causes them to fold into an alpha-helical shape, creating a rich, stable structure.

• Coil Structures: Two alpha-helices twist around each other, with hydrophobic residues found in the core to avoid interaction with water, stabilized by hydrophobic and Van der Waals interactions.

• Higher Order Structure: Keratin molecules cross-link through disulfide bonds, increasing strength.

Collagen

• Repetitive Structure: Features a three-amino-acid repeat, specifically having glycine at every first position and bulky amino acids (x and y) filling the remaining two spots.

• Importance of Glycine: The small size of glycine allows for tight packing, enabling the formation of a triple helix structure, crucial for its function and stability.

• Helical Structure: Formed through left-handed polyproline helical arrangements twisting to create a right-handed triple helix, which is stabilized by covalent interactions.

• Hydroxylation: Prolines and lysines can be hydroxylated, which is dependent on Vitamin C; insufficient Vitamin C can lead to weakened collagen and conditions like scurvy.

Myoglobin

• Function: Found in muscle tissue, myoglobin serves to increase oxygen solubility and facilitate diffusion rates necessary for energy metabolism.

• Structure:

  • Composed primarily of alpha helices (53 amino acids) and connecting loops, forming a globular structure; absence of beta sheets.

  • Contains a heme group, a non-protein component binding iron (Fe) that binds oxygen.

• Mechanism: The myoglobin structure allows it to effectively bind oxygen, increasing its solubility due to the hydrophobic pocket that hosts the heme group.

  • Heme group binding reduces its affinity for nonpolar gases like carbon monoxide.

Oxygen Binding and Myoglobin Properties

• Kinetics of Binding: The binding of oxygen involves kinetics where myoglobin concentration and oxygen concentration impact binding rates.

• Equilibrium: Describes a state where the rates of binding and release equal out; KD (dissociation constant) indicates binding strength and provides insight into protein affinity for oxygen.

• Saturation Curve: Myoglobin's binding curve is depicted as hyperbolic, illustrating how it binds oxygen relative to the concentration available. Myoglobin achieves maximum saturation quickly because of its structure.

Hemoglobin vs. Myoglobin

• Hemoglobin Features:

  • Composed of four subunits, allowing for cooperative binding, which increases the protein's efficiency in oxygen transport.

  • Exhibits a sigmoid-shaped binding curve due to cooperativity, allowing enhanced oxygen delivery to tissues where it's most needed.

• Allosteric Behavior: The switch between relaxed (R) and tense (T) states conveys different affinities for oxygen, thereby optimizing oxygen uptake and release during transport in the bloodstream.

Important Takeaways

• KD Importance: A lower KD signifies higher affinity, meaning the complex is more stable, allowing better binding in situations demanding high ligand concentrations.

• Application in Drug Development: Understanding these binding principles informs pharmaceutical design, targeting effective drug interactions with biological proteins.