supercomplex

A supercomplex is a supramolecular assembly of multiple protein complexes that perform related cellular functions, typically embedded in a membrane. In mitochondria, the term is most often used to describe respiratory chain supercomplexes, assemblies of electron transport chain complexes that work together to transfer electrons from NADH to oxygen. The best characterized examples involve complexes I, III and IV, arranged in various configurations, sometimes referred to as respirasomes. In some organisms, complex II can also participate in these assemblies.

Supercomplexes are not necessarily permanent fixtures; their formation and disassembly can depend on cellular conditions such as metabolic state, tissue type and aging. Their stability is influenced by factors including the lipid environment, notably cardiolipin, and specific protein–protein interactions. Proposed functional advantages include improved efficiency of electron transfer by reducing the diffusion distance between successive redox centers, possible substrate channeling, and lowered production of reactive oxygen species. Nevertheless, the functional significance of each observed supercomplex remains a topic of investigation, and some researchers contend that certain associations may reflect transient encounters or assembly intermediates rather than stable, active units.

Beyond mitochondria, similar supramolecular assemblies occur in chloroplasts and cyanobacteria, where photosynthetic complexes organize into higher-order structures to optimize light-driven electron transport. The study of supercomplexes has benefited from techniques such as blue native polyacrylamide gel electrophoresis and cryo-electron microscopy, which have revealed diverse architectures and dynamic behavior across organisms.