Plant and mammalian sorting signals for protein retention in the endoplasmic reticulum contain a conserved epitope.

Abstract

We studied protein sorting signals which are responsible for the retention of reticuloplasmins in the lumen of the plant endoplasmic reticulum (ER). A non‐specific passenger protein, previously shown to be secreted by default, was used as a carrier for such signals. Tagging with C‐terminal tetrapeptide sequences of mammalian (KDEL) and yeast (HDEL) reticuloplasmins led to effective accumulation of the protein chimeras in the lumen of the plant ER. Some single amino acid substitutions within the tetrapeptide tag (‐SDEL, ‐KDDL, ‐KDEI and ‐KDEV) can cause a complete loss of its function as a retention signal, demonstrating the high specificity of the retention machinery. However, other modifications confer efficient (‐RDEL) or partial (‐KEEL) retention. It is also shown that the efficiency of protein retention is not significantly impaired by an increased ligand concentration in plants. The efficiently retained chimeras (‐KDEL, ‐HDEL and ‐RDEL) were shown to be recognized by a monoclonal antibody directed against the C‐terminus of the mammalian reticuloplasmin protein disulfide isomerase (PDI). The recognized epitope is also present in several putative reticuloplasmins in microsomal fractions of plant and mammalian cells, suggesting that the antibodies recognize an important structural determinant of the retention signal. In addition, data are discussed which support the view that upstream sequences beyond the C‐terminal tetrapeptide can influence or may be part of the structure of reticuloplasmin retention signals.

Molecular characterization and transcriptome profiling of expansin genes isolated from Calotropis procera fibers

“…The presence of the signal anchor sites and the hydrophobic region comprising the transmembrane segment at the N-terminus (Table 4) suggested the insertion of this region as a loop in the central cavity of translocon (protein lined channel within the ER membrane). The absence of the ER retention signals (KDEL or HDEL as proposed by Denecke et al 1992) in CpEXPA1, CpEXPA2, CpEXPA3 and CpEXPA4 and the secretory nature of these proteins suggested that these were targeted to the cell wall as assumed for members of Expansin A families in other plants (Cosgrove, 2000). The secretion of the C. procera fiber expansin is consistent with previous findings that expansin proteins are associated with plant cell walls and play key role in enlargement of the growing cell.…”

Overexpression of Multiple Dehydrin Genes Enhances Tolerance to Freezing Stress in Arabidopsis

“…Plasmids containing DHN cDNAs, pRAB18R, pLTI29R, pLTI30R and pCOR47R (Svensson et al, 2000) were restricted with PstI followed by NcoI restriction. The PstI site was blunted and the full-length cDNAs of the DHN genes were ligated to pDE312 vector (NcoI and XbaI/blunt) (Denecke et al, 1992), which contains the 35S promoter and the 3¢nopaline synthase (3'nos) termination signals. The resulting plasmids were named pTP1 (COR47), pTP2 (RAB18), pTP3 (LTI29) and pTP4 (LTI30).…”

A novel extracellular matrix protein from tomato associated with lignified secondary cell walls.

“…Analysis of the predicted amino acid sequence revealed an N-terminal region with characteristics of a signal peptide (von Heijne, 1986) and a predicted cleavage site at positions 26 and 27. The absence of an endoplasmic reticulum retention signal (KDELor HDEL) (Denecke et al, 1992) suggests that the processed protein is exported from the endoplasmic reticulum once it is synthesized. Particularly interesting in the deduced amino acid sequence of this protein is the high degree of homology of the N-terminal region of the preprotein with that of different GRPs, including that of tobacco (van Kan et al, 1988), carrot (EMBL accession number X15706), Chenopodium (Kaldenhoff and Richter, 1989), and tomato (Showalter et al, 1991) ( Figure 1D).…”