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

• Published in: The EMBO journal 1992-06, Vol.11 (6), p.2345-2355
• Main Authors: Denecke, J, Rycke, R. de, Botterman, J
• Format: Article
• Language: English
• Subjects: acyltransferases; Amino Acid Sequence; amino acid sequences; amino acids; Animals; Antibodies, Monoclonal; Biological and medical sciences; Biological Evolution; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; characterization; Chimera; Cloning, Molecular; endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; Epitopes; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; genetic transformation; genetically modified organisms; Golgi Apparatus - metabolism; Golgi Apparatus - ultrastructure; immunocytochemistry; Isomerases - metabolism; Mammals; Microsomes - metabolism; Molecular and cellular biology; Molecular Sequence Data; Nicotiana - genetics; Nicotiana - metabolism; Nicotiana tabacum; phosphinothricin acetyltransferase; plant proteins; Plants - genetics; Plants - metabolism; Plants, Genetically Modified; Plants, Toxic; Protein Disulfide-Isomerases; protein secretion; Protein Sorting Signals - metabolism; protoplasts; requirements; retention; retention signals; reticuloplasmin; reticuloplasmins; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Sequence Homology, Nucleic Acid; signal peptide
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1002/j.1460-2075.1992.tb05294.x

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.