Multisubunitaires

Multisubunitaires is a term used in biology to describe protein assemblies composed of two or more subunits that assemble to execute cellular functions. The subunits may be identical or distinct polypeptides. Such complexes exhibit modular architecture, where a scaffold or core provides structural integrity and facilitates coordination of catalytic or binding activities by auxiliary subunits.

Subunit composition can vary across tissues or developmental stages. Subunits may be produced separately and assembled in the cytoplasm or nucleus, or during translation; assembly factors and chaperones guide correct stoichiometry and folding. Many multisubunit complexes display dynamic composition, exchanging subunits in response to signals, thereby altering activity, specificity, or localization. Post-translational modifications further regulate assembly and function.

Prominent examples include the proteasome, a proteolytic machine composed of a core particle and regulatory particles; RNA polymerase II, which requires multiple subunits to form a functional enzyme; ATP synthase, with its soluble F1 sector and membrane-embedded Fo sector; and photosynthetic complexes such as photosystem II. In energy metabolism and gene expression, multisubunit architecture enables coordination of catalysis with substrate access, regulation, and substrate channeling.

Evolution often expands functional diversity by duplicating subunits or mixing paralogs; comparative genomics reveals conserved cores with lineage-specific subunits. Investigative approaches such as cryo-electron microscopy, X-ray crystallography, cross-linking mass spectrometry, and quantitative proteomics illuminate subunit organization, interfaces, and dynamics. Malfunction or misassembly of multisubunit complexes can contribute to disease, highlighting their biological importance and potential as therapeutic targets.