Dilysine motifs

The vesicles used in the retrograde transport from the Golgi to the ER are coated by the COP I protein, whereas in the anterograde transport from the ER to the Golgi, the COP II protein seems to be a principal player. The dilysine motif turned out to interact with COP I, directing the retrieval to the ER. This is plausible because COP I exists on the cytosolic surface of the Golgi membrane. 

Ste24p is predicted to have seven transmembrane spans by hydropathy analysis. Experimental evidence supports the view that the N-terminus of Ste24p is luminal and its C-terminus is cytsolic, consistent with the predicted odd number of spans [54]. The C-terminus of Ste24p contains a dilysine ER retrieval motif (KKXX), and the protease is dually localized to the ER and the INM [5,48,58]. Importantly, the Ste24p zinc metalloprotease motif (HEXXH), which lies within a large cytosolic loop between the two C-terminal membrane spans, is appropriately cytosolically positioned for processing of a membrane-bound prenylated substrate such as a-factor. 

Gidda, S.K., Shockey, J.M., Rothstein, S.J., Dyer, J.M., Mullen, R.T., 2009. Arabidopsis thaliana GPAT8 and GPAT9 are localized to the ER and possess distinct ER retrieval signals functional divergence of the dilysine ER retrieval motif in plant cells. Plant Physiol. Biochem. 47, 867-879. 

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