Programmed cell death (PCD) is a prerequisite for successful development and it limits the spread of biotrophic pathogens in a rapid hypersensitive response at the site of infection. KDEL-tailed cysteine endopeptidases (KDEL CysEP) are a subgroup of papain-type cysteine endopeptidases expressed in tissues undergoing PCD. In Arabidopsis, three KDEL CysEPs (AtCEP1, AtCEP2, and AtCEP3) are express...

A vacuolar cysteine proteinase, designated SH-EP, is expressed in the cotyledon of germinated Vigna mungo seeds and is responsible for the degradation of storage proteins. SH-EP is a characteristic vacuolar proteinase possessing a COOH-terminal endoplasmic reticulum (ER) retention sequence, KDEL. In this work, immunocytochemical analysis of the cotyledon cells of germinated V. mungo seeds was p...

Electron microscope immunocytochemistry reveals that both anterograde-directed (proinsulin and VSV G protein) and retrograde-directed (the KDEL receptor) cargo are present in COPI-coated vesicles budding from every level of the Golgi stack in whole cells; however, they comprise two distinct populations that together can account for at least 80% of the vesicles budding from Golgi cisternae. Segr...

Retention of soluble proteins in the endoplasmic reticulum is dependent on their interaction with the KDEL (Lys-Asp-Glu-Leu) receptor in the Golgi apparatus and their subsequent retrieval back to the endoplasmic reticulum. We have studied the three-dimensional organization of the human KDEL receptor using site-directed mutagenesis and sulfhydryl-specific labeling. We have identified four amino ...

The function of KDEL receptors (KDELR) is to capture endoplasmic reticulum (ER)-resident chaperones in the acidic environment of the Golgi apparatus, by recognizing their C-terminal motif, and retrieve them back to the ER [1]. Certain structural features of KDELR, for example a similar topology to that of G-protein-coupled receptors (GPCR), a large family of proteins involved in virtually all p...

The plant A/B toxin ricin represents a heterodimeric glycoprotein belonging to the family of ribosome inactivating proteins, RIPs. Its toxicity towards eukaryotic cells results from the depurination of 28S rRNA due to the N-glycosidic activity of ricin toxin A chain, RTA. Since the extention of RTA by a mammalian-specific endoplasmic reticulum (ER) retention signal (KDEL) significantly increase...

Three forms of interleukin-6 (IL-6) have been constructed and stably transfected into human hepatoma cells (HepG2). Wild type IL-6 containing a signal peptide was rapidly secreted as a biologically active protein. IL-6 lacking the signal peptide accumulated within the cytoplasm of transfected cells. Surprisingly, IL-6 carrying a COOH-terminal extension of the amino acids Lys-Asp-Glu-Leu (KDEL) ...

An Escherichia coli expression system was used to produce recombinant ricin A chain (RTA) and RTA modified either by the addition of a carboxyl-terminal endoplasmic reticulum retrieval sequence Lys-Asp-Glu-Leu (RTAKDEL) or a nonfunctional analogue Lys-Asp-Glu-Ala (RTAKDEA). These RTA molecules can enter mammalian cells by fluid phase endocytosis. RTAKDEL was significantly more cytotoxic than ei...