Golgi apparatus: Homotypic fusion maintains biochemical gradients within the Golgi and improves the accuracy of protein maturation

Eukaryotic cells are compartmentalized into organelles which, although constantly exchanging proteins and lipids with their environment, maintain a relatively well-defined biochemical identity. How can such large heterogeneities of chemical composition between (and within) organelles be maintained if different organelles are in constant contact through mass transport? Generic nonlinearities in the transport processes, as would result from specific molecular interactions, can cause the spontaneous chemical differentiation of interacting organelles and compartments within organelles. For the Golgi apparatus, the role of which is to process an incoming flux of lipids and proteins, this spontaneous differentiation decreases inter-cisternal exchange and increases the protein transit time under conditions of high incoming flux, This mechanism enables the Golgi apparatus to spontaneously adjust the protein transit time to the amount of protein requiring processing, thereby improving the processing accuracy of even a limited amount of maturation enzymes.