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Mechanism of translocon function: current insights and models
A selection of talks on Biochemistry
The ERK1/2 MAPK cascade
- Prof. Melanie H. Cobb
- University of Texas Southwestern Medical Center at Dallas, USA
Amino acid conjugation: mechanism and enzymology
- Dr. Kathleen Knights
- Flinders University, Australia
Hello, my name is Arnold Driessen. I'm a professor at the Department of Molecular Microbiology at the University of Groningen in the Netherlands. Today, I would like to discuss with you the mechanism of translocon function, in particular, current insights and models. But before doing so, let's first have a look at the organization of the eukaryotic cell.
This slide shows a typical scheme of a eukaryotic cell. And all its membrane-bound organelles, like for instance the vacuole, the peroxisome, the mitochondria, the nucleus, and the endoplasmic reticulum, and many other organelles. Each of these organelles contains specific subset of proteins, which provides a specific function to this organelle. Proteins are synthesized either on free ribosomes in the cytosol, or on ribosomes bound to the endoplasmic reticulum. These proteins, they need to end up at a specific localization, and for that purpose, they contain specific labels, like for instance, signal sequences that mediate targeting at the various organelles, there are translocation machineries that translocate these proteins from the cytosol into the organelle. Proteins destined to be secreted are synthesized on ribosomes bound to the endoplasmic reticulum. Once they are translocated across the endoplasmic reticulum membrane, they are sorted via vesicle sorting route to the external medium and to the plasma membrane. But if we now look at the bacterial cell, the left-hand corner, we're struck by the simplicity of this bacterial cell. In contrast to, for instance, a eukaryotic cell, which may have up to 50 different organelles. You observe a lesser complexity in compartmentalization in these bacteria. Proteins are synthesized in the cytosol. Some of these proteins have to function in the cytosol, whereas others are targeted to the external organelles. Like for instance, the inner membrane, the periplasm which is the space in between the inner membrane and the outer membrane. The outer membrane and the external medium. These are also compartments, and each of these compartments contains a specific subset of proteins which provides a specific function to these compartments. Even though we are dealing with less complexity, the bacterial cell has to solve the same problem as a eukaryotic cell. Proteins need to be targeted to specific compartments.