Cells of higher organisms have several different compartments. Bacteria are relatively simple cells with only one or two different compartments. The most important protein translocation system in bacteria is similar to one also found in higher organisms, including humans. Escherichia coli and other bacteria have a ubiquitous transport system known as the Sec pathway, and the core component SecYEG consists of three different membrane proteins SecY, SecE, and SecG. Most Escherichia coli proteins that are not destined for the main, cytoplasmic compartment, are transported by the SecYEG complex, including those destined for insertion into the membrane itself. They typically contain a signal sequence, which acts like a post-code and is recognized by the transport machinery. Proteins are then transported through a channel formed by the SecYEG complex.
Researchers at the Max Planck Institute of Biophysics in Frankfurt have now determined the first structure of the SecYEG protein translocation machinery from the bacterium Escherichia coli. They were able to grow small, two-dimensional crystals of the membrane-inserted complex, and determined its structure by electron cryo-microscopy and image processing.
The structure for the first time provides a detailed view of a protein-transporting machine (Figure 1 & 2). The images show a so called "dimer"(chunk or unit) of the SecYEG complex in its native environment, the lipid membrane. The dimer is thought to be the active form of the complex, which bi
Contact: Dr. Ian Collinson