Prolyl 3-hydroxylase 1 (P3H1), encoded by the LEPRE1 gene, forms a molecular complex with cartilage-associated protein (CRTAP) and cyclophilin B (encoded by PPIB) in the endoplasmic reticulum (ER). This complex is responsible for one step in collagen post-translational modification, the prolyl 3-hydroxylation of specific proline residues, specifically α1(I) Pro986. P3H1 provides the enzymatic a...

Recently we found by immunogold electron microscopy that protein disulfide-isomerase (PDI), a major resident protein in the lumen of the endoplasmic reticulum (ER) of many cells, is exceptionally localized in rat exocrine pancreatic cells not only in the ER but also in plasma membranes and other organelles along secretory pathway (Akagi, S., Yamamoto, A., Yoshimori, T., Masaki, R., Ogawa, R., a...

A/B toxins such as cholera toxin, Pseudomonas exotoxin and killer toxin K28 contain a KDEL-like amino acid motif at one of their subunits which ensures retrograde toxin transport through the secretory pathway of a target cell. As key step in host cell invasion, each toxin binds to distinct plasma membrane receptors that are utilized for cell entry. Despite intensive efforts, some of these recep...

During virus infection of insect cells, the Autographa californica nucleopolyhedrovirus chitinase is localized primarily within the endoplasmic reticulum (ER), which is consistent with the presence of a carboxy-terminal ER retention motif (KDEL). Release of chitinase into the extracellular medium appears to be concomitant with terminal cell lysis, rather than by active secretion. In this study,...

Many soluble resident proteins of the endoplasmic reticulum share a COOH-terminal Lys-Asp-Glu-Leu (KDEL) sequence. Current opinion favours a model in which these proteins can escape from the endoplasmic reticulum (ER) by bulk flow and are recognized and sorted in the Golgi apparatus by binding to a specific KDEL-receptor, which returns them to the ER. Through biochemical, morphological and muta...

In a prior report we presented evidence that insulinlike growth factor-I (IGF-I) can act in an autocrine fashion by demonstrating that FRTL-5 cells transfected with hIGF-IA fusion genes express and secrete biologically active IGF-I that renders the stimulation of DNA synthesis in FRTL-5 cells independent of heir requirement for exogenous IGFs or insulin. To determine if IGF-1’s autocrine action...

Soluble luminal proteins of the endoplasmic reticulum (ER) are known to be retained by a tetrapeptide retention signal, KDEL. We report in this communication that the KDEL sequence when appended to the carboxy terminus of a cell surface membrane protein, dipeptidyl peptidase IV (DPPIV), resulted in its retention in the endoplasmic reticulum of transfected Madin-Darby canine kidney cells as asse...

How the occupied KDEL receptor ERD2 is sorted into COPI vesicles for Golgi-to-ER transport is largely unknown. Here, interactions between proteins of the COPI transport machinery occurring during a "wave" of transport of a KDEL ligand were studied in living cells. FRET between CFP and YFP fusion proteins was measured by multifocal multiphoton microscopy and bulk-cell spectrofluorimetry. Ligand ...

The ricinosome (synonym, precursor protease vesicle) is a novel organelle, found so far exclusively in plant cells. Electron microscopic studies suggest that it buds off from the endoplasmic reticulum in senescing tissues. Biochemical support for this unusual origin now comes from the composition of the purified organelle, which contains large amounts of a 45-kDa cysteine endoprotease precursor...

Seeds possess a high intrinsic capacity for protein production that makes them a desirable bioreactor platform for the manufacture of transgenic products. One strategy to enhance foreign protein production involves exchanging the capacity to produce intrinsic proteins for the capacity to produce a high level of foreign proteins. Suppression of the alpha/alpha' subunit of beta-conglycinin storag...