homotrimeric

Homotrimeric refers to a molecular complex formed by three identical subunits that assemble to function as a single unit. In proteins, a homotrimer arises when three copies of the same polypeptide associate non-covalently to create a threefold symmetric assembly. This is distinct from heterotrimeric assemblies, which contain three different subunits.

Structure and symmetry: Homotrimers often exhibit threefold rotational symmetry (C3) and rely on interfaces that include hydrophobic contacts, hydrogen bonds, and salt bridges between subunits. The trimeric arrangement can stabilize active sites, generate multivalent ligand-binding surfaces, and enable communication between subunits for coordinated activity.

Biosynthesis and assembly: Monomeric subunits are produced individually and assemble into the trimer in a process that may involve chaperones or the cellular folding environment. The stability of a homotrimer depends on the strength of inter-subunit interfaces and can be influenced by factors such as pH, ionic strength, and ligand binding.

Function: Homotrimers contribute to signaling, catalysis, and structural roles by providing coordinated activity and higher binding avidity. They allow cooperative interactions and can enable allosteric regulation where binding at one subunit affects others.

Examples and significance: Notable examples include tumor necrosis factor (TNF) family cytokines, which commonly form homotrimers that engage TNF receptors. Viral envelope glycoproteins such as coronavirus spike proteins and influenza hemagglutinin are also homotrimers, a feature relevant to entry and immune recognition. Understanding homotrimeric organization informs fields from drug design to nanotechnology, where targeting interfacial contacts can disrupt or stabilize the complex.