Compartmentscytosol

Compartmentscytosol is a concept in cell biology that describes how the cytosolic space is organized into functional subregions or compartments to regulate and concentrate biochemical reactions. This organization encompasses both traditional membrane-bound organelles that reside in the cytosol and membrane-less, dynamic assemblies that form within the cytoplasm. The term emphasizes spatial separation and proximity of enzymes, substrates, and regulatory factors to enhance efficiency and control.

Within the cytosol, two broad classes of compartments are recognized. Membrane-bound organelles such as mitochondria, lysosomes, and the endoplasmic reticulum create defined spaces in the cytosol with specialized environments. In addition, membrane-less condensates—often formed by liquid-liquid phase separation—gather proteins and RNAs into dense, dynamic bodies. Examples include stress granules, processing bodies (P bodies), and various signaling clusters near the plasma membrane. Cytosolic compartments also arise from organized protein complexes and cytoskeletal tracks that channel substrates to specific enzymes, a concept sometimes described as metabolons or enzyme neighborhoods.

Formation and regulation of cytosolic compartments depend on multivalent interactions among proteins and RNAs, post-translational modifications, and cellular conditions. Phase separation can create reversible, rapidly tunable environments that isolate or concentrate reactions, filter molecules by size or chemistry, and protect labile intermediates from interference.

Disruption of cytosolic compartmentalization is linked to disease in some contexts, including neurodegenerative disorders and cancer, where altered phase behavior or mislocalization of key components can impair metabolism and signaling. Studying these compartments employs advanced imaging, biophysical reconstitution, and high-resolution proteomics to understand their composition, dynamics, and functional roles.