Collagens and tropocollagens Collagens and tropocollagens:Serpin H1 Secretion of collagens Authored: Jupe, S, 2010-07-20 Collagen precursors are co-translated into the ER, where post-translational modifications occur that are essential for oligomerization and stabilization, the latter thought to involve Serpin H1 (HSP47). Trimers are exported from the ER and trafficked through the Golgi network before secretion into the extracellular space and organization into higher order structures. The precise route and mechanism of secretion for collagen is unclear (Canty & Kadler 2005). In the conventional protein secretion pathway cargo is collected at ER exits sites and loaded into small membrane vesicles that are generated by a set of highly conserved proteins called the coat protein complex II (COPII) (Jensen & Schekman 2011). However, these small vesicles of 60-90 nm diameter are too small for collagens some of which assemble in the ER into 300-400 nm rod-like structures. Collagen secretion appears to involve a modification of the COPII process involving TANGO1 and cTAGE5 which form a dimer at ER exit sites (Malhotra & Erlmann 2011). TANGO1-null mice die at birth and are defective in the secretion of a number of different collagens (Wilson et al. 2011). Another recent study suggests that ubiquitination of one of the COPII complex proteins, SEC31, is sufficient to allow formation of vesicles that are large enough to hold procollagen (Jin et al. 2012). Edited: Jupe, S, 2012-05-14 Pubmed15788652 Pubmed21172817 Pubmed21606205 Pubmed21878990 Pubmed21967573 Pubmed22358839 Reactome Database ID Release 432089971 Reactome, http://www.reactome.org ReactomeREACT_121366 Reviewed: Canty-Laird, EG, 2012-05-24