FIGURE 7.

A model of Cosmc function in the biosynthesis of T-synthase. A, a working model is presented for Cosmc function in T-synthase biosynthesis. It is proposed that the ER-localized Cosmc directly interacts with co-translationally translocated non-native T-synthase and promotes its refolding independently of other factors. Cosmc forms a transient complex with active T-synthase and active T-synthase is released from Cosmc complex when Cosmc interacts with other co-translationally translocated non-native T-synthase or native T-synthase for another cycle of refolding. Active dimeric T-synthase exits to the Golgi apparatus. In the absence of functional Cosmc, the T-synthase aggregates and is degraded by proteasomal machinery. B, simplified equilibria and folding kinetics of T-synthase in the presence and absence of Cosmc relative to the fate of correctly or incorrectly folded T-synthase.