heterotrimert

Heterotrimers are molecular complexes composed of three distinct polypeptide subunits. These subunits, being different from each other, are what define the "hetero" aspect of the name, distinguishing them from homotrimers which are made of three identical subunits. The assembly of these three different proteins into a stable, functional unit is a crucial process in many biological systems.

The interaction between the subunits in a heterotrimer is mediated by non-covalent forces such as hydrogen bonds, ionic interactions, and van der Waals forces, although in some cases, disulfide bonds can also contribute to stability. The specific arrangement and interaction surfaces of the subunits determine the overall structure and function of the heterotrimer.

Heterotrimers play vital roles in a wide array of cellular processes. A prominent example is their involvement in signal transduction pathways. G protein-coupled receptors (GPCRs), for instance, interact with heterotrimeric G proteins, which consist of alpha, beta, and gamma subunits. Upon activation of the GPCR, the alpha subunit exchanges GDP for GTP, leading to dissociation of the alpha subunit from the beta-gamma dimer. Both the free alpha subunit and the beta-gamma dimer can then go on to regulate downstream effectors, illustrating the functional significance of these tripartite complexes. Other examples include certain enzymes, ion channels, and protein-protein interaction modules that are assembled as heterotrimers. The precise composition of a heterotrimer can often determine its specificity and efficacy in carrying out its biological function.