FIGURE 7.

Proposed model of Cosmc function. In this model newly synthesized T-synthase co-translationally translocates into the lumen of the ER and directly interacts with Cosmc through the CBRT region (blue). Such interaction prevents the formation of an inactive oligomeric complex of T-synthase, which is removed to the cytoplasm and degraded. Binding of T-synthase to Cosmc promotes the formation of a transient complex, resulting in the folding of T-synthase. Active T-synthase is released from the complex when Cosmc interacts with other co-translationally translocated non-native T-synthase for another possible cycle of refolding (19). The CBRT region with the active and released T-synthase is no longer accessible to binding by Cosmc.