Figure 8.

Proposed working model for GnTI retrieval and its steady-state localization in the cis/medial-Golgi. The model proposes a TMD-motif–based sorting including the retrograde transport from the trans-Golgi with COPI variants (e.g. COPIb; Donohoe et al., 2007). The TMD sequence motif with the conserved Gln is either required for a specific protein-protein interaction with an adaptor protein (indicated on the right side) or for interaction with a specific lipid class or Golgi membrane environment (indicated on the left side) that partitions GnTI into retrograde transport carriers to concentrate the glycosyltransferase in cis/medial-Golgi membranes. The large black arrows indicate cargo that is transported from the ER trough the Golgi apparatus.