Homotrimer

Homotrimer

A homotrimer is a type of protein complex that consists of three identical subunits. These subunits are non-covalently bonded and interact with each other to form a stable, functional unit. Homotrimers are a subset of oligomeric proteins, which are proteins composed of multiple subunits.

Structure

Homotrimers are characterized by their symmetrical structure, where each subunit is identical in sequence and conformation. The three subunits are arranged in a way that often results in a threefold rotational symmetry. This symmetry is crucial for the stability and function of the homotrimer.

The interface between the subunits is typically rich in hydrophobic interactions, hydrogen bonds, and sometimes disulfide bonds, which contribute to the overall stability of the complex. The specific arrangement and interactions at the interface can vary depending on the protein and its function.

Function

Homotrimers can serve a variety of functions in biological systems. Some common roles include:

• Structural support: Homotrimers can form part of the structural framework of cells and tissues. For example, collagen is a well-known structural protein that can form homotrimeric structures.

• Enzymatic activity: Some enzymes are homotrimers, where the trimeric structure is essential for their catalytic activity. The active site may be formed at the interface of the subunits.

• Signal transduction: Homotrimers can be involved in signaling pathways, where they act as receptors or signaling molecules. For instance, certain cytokine receptors are homotrimeric.

Examples

• Collagen: As mentioned, collagen can form homotrimeric structures, particularly in its triple-helix form, which is crucial for its role in providing tensile strength to tissues.

• Tumor necrosis factor (TNF): TNF is a cytokine that forms a homotrimeric structure, which is important for its role in inflammation and apoptosis.

• Aldolase: This enzyme, involved in glycolysis, can form a homotrimer, which is necessary for its function in catalyzing the cleavage of fructose-1,6-bisphosphate.

Also see

• Protein quaternary structure
• Heterotrimer
• Dimer (chemistry)
• Oligomer