Biomedical subjects

B Jungnickel

Publications and source records attributed to B Jungnickel.

5 recordsLinked to original sources

PubMed1995

Signal sequence processing in rough microsomes.

Secretory proteins are synthesized with a signal sequence that is usually cleaved from the nascent protein during the translocation of the polypeptide chain into the lumen of the endoplasmic reticulum. To determine the fate of a cleaved signal sequence, we used a synchronized in vitro translocation system. We found that the cleaved signal peptide of preprolactin is further processed close to its COOH terminus. The resulting fragment accumulated in the microsomal fraction and with time was released into the cytosol. Signal sequence cleavage and processing could be reproduced with reconstituted vesicles containing Sec61, signal recognition particle receptor, and signal peptidase complex.

Amino Acid Sequence↗

PubMed1995

A posttargeting signal sequence recognition event in the endoplasmic reticulum membrane.

We have analyzed early phases of the cotranslational transport of the secretory protein preprolactin through the mammalian endoplasmic reticulum (ER) membrane. Following recognition of the signal sequence of the nascent polypeptide chain in the cytosol by the SRP, the chain is transferred into the membrane, where a second signal sequence recognition step takes place for which the presence in the lipid bilayer of the Sec61p complex is essential and sufficient. This step leads to a tight junction between the ribosomenascent chain complex and the Sec61p complex, and to the productive insertion of the nascent chain into the translocation site. These results show that a translocation substrate is subjected to two recognition events before being allowed to cross the ER membrane.

Amino Acid Sequence↗

PubMed1995

The Sec61 complex is essential for the insertion of proteins into the membrane of the endoplasmic reticulum.

Cross-linking studies have implicated Sec61 alpha as the principal component adjacent to newly synthesised membrane proteins during insertion into the endoplasmic reticulum. Using proteoliposomes which have been reconstituted from purified components of the endoplasmic reticulum [Görlich, D and Rapoport, T.A., Cell 75 (1993) 615-630] we have found that the Sec61 complex, consisting of three subunits, is essential for the insertion of single-spanning membrane proteins. This is true for signal-anchor proteins of both orientations, and for proteins with a cleavable signal sequence. These results support the view that Sec61 alpha is a major component of the ER translocation site and promotes both the insertion of membrane proteins and the translocation of secretory proteins.

Endoplasmic Reticulum↗

PubMed1994

Protein translocation: common themes from bacteria to man.

Protein transport across the endoplasmic reticulum membrane in eukaryotes and across the cytoplasmic membrane in bacteria have turned out to be highly related. The core component of the translocation apparatus is the Sec61/SecYp complex; at least two of its subunits are conserved in evolution. The Sec61/SecYp complex is involved in both co- and post-translational transport pathways. The two modes require probably distinct additional components.

Bacteria↗

PubMed1993

DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) inhibits an early step of protein translocation across the mammalian ER membrane.

Protein translocation across the endoplasmic reticulum (ER) membrane of yeast can be inhibited by agents believed to specifically affect the transport of ATP through the membrane (Mayinger, P. and Meyer, D.I. (1993) EMBO J. 12, 659-666), suggesting the involvement of a translocation component in the lumen of the ER that binds ATP. We demonstrate that one of the inhibitors, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), also affects the translocation of proteins into mammalian microsomes. Translocation is blocked at the point of transfer of the nascent chain from the signal recognition particle (SRP) into the ER-membrane. We also confirm that photoaffinity-labelling of microsomes with 8-azido-ATP inhibits the same early step of protein translocation. Since this step is reported to not require ATP, these results raise the possibility that, in both cases, factor(s) other than ATP-binding components of the translocation machinery are perturbed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗