Secretory proteins, segregation

Studies with VSV and SFV were the first to show that membrane glycoproteins make use of the same mechanisms used by secretory proteins to become segregated into the ER lumen (Katz et al., 1977 Rothman and Lodish, 1977 Wirth et al., 1977 Lingappa et al., 1978 ... 

Translocation of Proteins Across Membranes. The transfer of proteins across biological membranes generally involves a hydrolytic modification step of the precursor form of the mature protein. This processing has been shown clearly to occur during segregation of secretory proteins, transport of proteins into mitochondria, and entry of plant and microbial toxins into cells as shown in Table XII. 

The immediate segregation of proteins in the ER suggested that translocation across the membrane may be coupled to translation. The experiments of Redman and Sabatini (1966) supported this concept on a molecular level. After addition of puromycin, an inhibitor of protein elongation, to growing cells, N-terminal fragments of secretory proteins were found in the lumen of the ER, and not in the cytoplasm. In later work, Sabatini and Blobel (1970) showed that inclusion of microsomes of RER in a cell-free system translating mRNA coding for secretory pro-... 

The trans Golgi network (TGN) is a major branch point In the secretory pathway where soluble secreted proteins, lysosomal proteins, and In some cells membrane proteins destined for the basolateral or apical plasma membrane are segregated Into different transport vesicles. 

Signal hypothesis A mechanism proposed by Blobel for the segregation of secretory proteins during their biosynthesis. It has since been found applicable to most proteins which are either inserted into membranes or transported across them, including organelle proteins which are synthesized in the cytosol. Such proteins are transcribed with a signal or leader peptide of 15 to 30 amino acid residues About 70... 

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