Cellular microcompartments constitute general suborganellar functional units in cells

All cells are compartmentalized to facilitate enzymatic reactions or cellular dynamics. In eukaryotic cells, organelles differ in their protein/lipid repertoire, luminal ion composition, pH, and redox status. In addition, organelles contain specialized subcompartments even within the same membrane or within its lumen. Moreover, the bacterial plasma membrane reveals a remarkable degree of organization, which is recapitulated in eukaryotic cells and often linked to cell signaling. Finally, protein-based compartments are also known in the bacterial and eukaryotic cytosol. As the organizing principle of such cellular subcompartments is likely similar, previous definitions like rafts, microdomains, and all kinds of ‘-somes’ fall short as a general denominator to describe such suborganellar structures. Within this review, we will introduce the term as a general suborganellar functional unit and discuss its relevance to understand subcellular organization and function.