Optineurin is an adaptor protein for ubiquitinated substrates in Golgi membrane-associated degradation

Golgi membrane-associated degradation (GOMED) is a process that leading to the degradation of proteins that have passed through the trans-Golgi membranes upon Golgi stress. GOMED is morphologically similar to autophagy, but the substrates degraded are different, and they thus have different biological roles. Although the substrate recognition mechanism of autophagy has been clarified in detail, that of GOMED is completely unknown. Here we report that GOMED degrades its substrate proteins selectively via optineurin (OPTN), as we found that the degradation of GOMED substrates is s`uppressed by the loss of OPTN. OPTN binds to K33 polyubiquitin-tagged proteins that have passed through the Golgi, which are then incorporated into GOMED structures for eventual degradation. In vivo, GOMED is known to be involved in the removal of mitochondria from erythrocytes, and in Optn-deficient mice, mitochondria are not degraded by GOMED, resulting in the appearance of erythrocytes containing mitochondria. These findings provide insight into the substrate recognition mechanism of GOMED.