Merged picture of KR-10 (red) with DAPI (blue) in NRK cells.
Courtesy of Institute of Molecular and Cell Biology, Singapore.

The endoplasmic reticulum is part of a protein sorting pathway, or in
essence, the transportation system of the eukaryotic cell. The majority
of endoplasmic reticulum resident proteins are retained in the
endoplasmic reticulum through a retention motif. This motif is composed
of four amino acids at the C-terminal end of the protein sequence. The
most common retention sequence is KDEL (lys-asp-glu-leu). However,
variation on KDEL does occur and other sequences can also give rise to
endoplasmic reticulum retention (6). There are three KDEL receptors in
mammalian cells, all have a very high degree of sequence identity; and
all are located within the cis-Golgi and its intermediate compartments
(4). In terms of function, KDEL receptors interact with GAP
(GTPase-activating protein) of ARF1, which is involved in COPI dependent
vesicle transport, and the KDEL receptor may also be responsible for
the recruitment of this ARF1 to membranes which can then aid in the
regulation of vesicle budding (3). It is also important to note that the
KDEL receptor exhibits extensive sequence identity o yeast protein
Erd2p, which is a receptor for the yeast ER retention signal (4, 5).

1. Whiteman P., and Handford P.A. (2003) Hum Mol Genet
2. Forthoffer N., et al. (2002) 12(7): 727-737. 34(3): 209-219. J Bioenerg Biomemb
3. Aoe T., et al. (1997) EMBO J. 16: 7305-7316.
4. Tang B.L., Wong S.H, Qi X.L. Low S.H., and Hong W. (1993) J. Cell Biol. 120: 325-328.
5. Lewis M.J. and Pelham H.R. (1990) Nature 348: 162- 163.
6. Spurger L. (2002). Endoplasmic reticulum: Structure and function.
University of Texas Medical Branch. Retrieved September 13, 2006, from
http://cellbio.utmb.edu/cellbio/rer1.htm