KDEL Proteins and Enzymes

The sequence Lys-Asp-Glu-Leu (KDEL) or a closely related sequence, is present at the carboxy-terminus of soluble endoplasmic reticulum (ER) resident proteins and some membrane proteins. 78 and 94 kDa glucose regulated proteins (GRP 78) and GRP 94 respectively and protein disulfide isomerase (PDI) all share the C-terminal KDEL sequence. The presence of carboxy-terminal KDEL appears to be necessary for ER retention and appears to be sufficient to reduce the secretion of proteins from the ER. This retention is reported to be mediated by a KDEL receptor.