Investigators Describe How Bacteria Form Syringe-Like Structure that Helps Infection

Scientists from the Max Planck Society and the Federal Institute for Materials Research and Testing have elucidated the basic principles of how bacteria create transport channels to deliver virulence factors.

The results appear in a paper titled “Protein refolding is required for assembly of the type three secretion needle” published June 13 in Nature Structural & Molecular Biology.

Some bacteria have developed a specialized transport mechanism called the type three secretion system. Electron microscopy reveals that this structure is formed like a syringe: The base of the syringe is embedded in the bacterial membrane and the needle protrudes out of the bacteria. But little has been known about how bacteria build this nano-syringe.

Close observation of these events revealed how the proteins are assembled into a syringe: The bacterium synthesizes the proteins in the cell interior, transports them through the syringe to the outside, and stacks them one after the other onto the tip of the growing needle. The scientists also showed that the proteins change their three-dimensional structure during the assembly process.

They were reportedly able to pinpoint the exact structural changes down to the single amino acid level. The change of the three-dimensional structure of the proteins during the needle assembly was analyzed by x-ray structural experiments and NMR-spectroscopic experiments based on radio waves. The scientists compared the three-dimensional structure of the needle protein before and after the needle assembly.