The "revolutionary technology" of the protein syringe

They manipulate their host's cells, defend themselves against predators or kill off competitors: many bacteria use sophisticated molecular nanosyringes to inject proteins into cells. These so-called contractile injection systems (CIS) can be reprogrammed and may be used therapeutically in many different ways in the future, as US researchers report in the journal Nature.

The team led by Feng Zhang from the Broad Institute in Cambridge (Massachusetts, USA) modified a bacterial nanosyringe in such a way that it could target active substances to specific cell types. The group writes that this could make various therapies possible, referring in particular to cancer treatments and gene therapies.

Clemens Wendtner from the Munich Clinic Schwabing speaks of a "revolutionary technology". "It seems that we are on the threshold of a new development," comments the doctor, who was not involved in the study. "Here there are no limits to the imagination with regard to future applications." Other experts also see a breakthrough in the study that could open up many options.

In the proof of concept, Zhang's team studied the injection system of the bacterium Photorhabdus asymbiotica, which originally targets insect cells. The molecular syringe - called the Photorhabdus virulence cassette (PVC) - consists of a tube about 100 nanometers (millionths of a millimeter) long. At its end, a so-called tail fiber binds to special receptors on the target cells so that the protein load can be guided through the cell membrane into these cells.

In systematic sub-tests, Zhang's team changed the injection devices in two main ways: On the one hand, they were able to initially inject other proteins that do not originate from P. asymbiotica into insect cells. Secondly, it reprogrammed the tail fibers in such a way that the nanosyringes attached to other cells, for example those of mice or humans.

For example, the researchers made sure that the injection system in the laboratory docked onto cells from lung tumors and killed them with a toxin. In another experiment, they introduced the Cas9 enzyme – the component of the Crispr-Cas9 gene scissors that can cut DNA – into human cells. This could potentially make it possible in the future to therapeutically modify the DNA in cells at desired targets.

In a final step, the team demonstrated the use of the nanosyringe on living organisms. By injecting them into the brains of mice, they smuggled proteins into nerve cells in the brain area of ​​the hippocampus. The researchers observed neither cell-damaging effects nor a strong activation of the immune system.

In addition, the injection apparatus was no longer detectable after one week. "This suggests that the system is ideally suited for therapies intended to be transient or short-term," the group notes.

The system presented makes it possible to "inject any proteins into cells with any defined structures on their surface," says Andreas Diepold from the Max Planck Institute for Terrestrial Microbiology in Marburg. Such an injection system, which can be loaded with foreign proteins, is a breakthrough.

However, experts point to a few hurdles: the protein load in the system is limited. In addition, it is important that this charge is only brought to the desired destinations and does not reach any other cells.

"The ability to introduce specific proteins into specific cell types would offer tremendous potential both for research in the life sciences and for the treatment of diseases," write Charles Ericson and Martin Pilhofer from the Swiss Federal Institute of Technology in Zurich (ETH). a "Nature" comment. "These transformed injection complexes represent an exciting biotechnological toolbox with applications in diverse biological systems."

Study leader Feng Zhang is a prominent figure in the life sciences. For the development of the Crispr-Cas9 gene scissors, he fought a bitter patent dispute with the two researchers Emmanuelle Charpentier, now founding director of the Max Planck Research Center for the Science of Pathogens, and Jennifer Doudna from the University of California at Berkeley.

They presented their work on the method in quick succession in 2012 in Science magazine. Charpentier and Doudna received the Nobel Prize for Medicine in 2020, Zhang went away empty-handed.