Supercomplexes

A supercomplex is a large assembly formed when two or more distinct enzyme complexes associate to function together as a single particle. In biology, such assemblies can coordinate successive biochemical steps, facilitate substrate channeling, stabilize components, and regulate activity in response to cellular conditions. The term is most commonly used to describe large respiratory and photosynthetic protein assemblies, but it can apply to other multiprotein complexes as well.

In mitochondria, respiratory chain supercomplexes organize parts of oxidative phosphorylation. The best-characterized form is a respirasome containing complexes I, III and IV (often I+III2+IV1), though assemblies can vary by organism, tissue, and metabolic state. The proposed advantages include reduced diffusion distances for ubiquinone and cytochrome c, improved efficiency of electron transfer, and stabilization of labile complexes. Assembly is dynamic and influenced by factors such as developmental stage, energy demand, and availability of lipids and assembly factors (for example, COX7A2L/SCAFI and members of the HIGD family). While some studies emphasize functional benefits, others debate whether supercomplex formation is essential or a byproduct of membrane organization; the topic remains active in mitochondria research.

In chloroplasts and photosynthetic organisms, supercomplexes form within the thylakoid membrane, including photosystems I and II with associated light-harvesting antennas. PSII–LHCII and PSI–LC complexes participate in light harvesting and state transitions that balance excitation energy. Structural and spectroscopic analyses, aided by cryo-electron microscopy and native proteomics, reveal detailed architectures and dynamic rearrangements that accompany environmental changes.

Research methods such as blue native PAGE, cryo-EM, cross-linking mass spectrometry and functional assays underpin current understanding of supercomplexes and their roles in energy metabolism.