1. Aggregation-mediated passive sorting of secretory and membrane proteins during the biogenesis of a secretory granule in the TGN. (1) The luminal contents of a TGN cisterna is depicted as consisting of a mixture of secretory proteins. One type (stars) is secreted constitutively, without being incorporated into secretory granules. (2) The two other types are capable of homophilic interactions and undergo self-aggregation in the milieu of the TGN. (3) Some integral membrane proteins of the TGN that are destined to become part of the secretory granule membrane bind specifically to one or the other aggregate. The clustering of these membrane proteins generates a granule membrane with a specific protein composition. In some cases (not shown) self-aggregating luminal proteins also exist in a membrane-bound form and the homophilic interaction between the soluble and the membrane-bound proteins leads to sorting of the secretory and membrane proteins into an immature granule. In other cases, two or more different types of luminal proteins undergo coaggregation, although only one type of protein may interact directly with membrane components.
Source: The Biogenesis of Membranes and Organelles, The Online Metabolic and Molecular Bases of Inherited Disease
Citation: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis SE, Ballabio A, Gibson K, Mitchell G. The Online Metabolic and Molecular Bases of Inherited Disease; 2014 Available at: Accessed: October 24, 2017
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