Molecular mechanisms of LOV-regulated diguanylate cyclases

Adaptation of all organisms to changing environmental conditions is based upon the coordinated action of many regulatory processes. External influences can be perceived by various sensors and this information is ultimately transmitted to diverse effectors. These effectors enable metabolic changes that eventually allow organisms to adapt to environmental changes. Light is one major environmental stimulus, and changes in both intensity and duration of exposure affect a wide variety of organisms. Over the course of evolution, a set of light-sensitive proteins have developed that can interact with different light qualities of the electromagnetic spectrum ranging from the ultra violet to the near infra-red region. As part of this project, a specific blue light photoreceptor family, in which the blue light sensor is directly coupled to a specific enzymatic functionality (diguanylate cyclase), will be characterized in detail. In this family, the production of a special compound (cyclic dimeric GMP) can be increased upon exposure to blue light, which in turn causes morphological changes in the organism. In the natural environment, microorganisms thereby alternate between motile and stationary life forms. Particularly in the case of pathogenic organisms, stable stationary forms of life, so-called biofilms, can be problematic for efficient antibiotic treatments. As part of the planned research activities, the molecular mechanisms of such blue-light-regulated diguanylate cyclases will be investigated in more detail, in order to understand how activation of the sensor domain leads to structural and functional changes in the coupled enzymatic effector. As a result, the better understanding of the underlying mechanisms will inform future semi-rational designs of novel sensor-effector combinations. Such non-naturally occurring blue light-regulated systems could then be used in the field of optogenetics, where genetically modified organisms can be treated with blue light in order to achieve specific biological effects. In the field of cell biology, for example, interactions between different proteins can be modulated by light and thus processes in living organisms can be controlled with high spatial and/or temporal resolution. In the long run, such systems might also find applications in the field of medicine, where localized light exposure could lead to pharmacologically active ingredients only being formed at the site of interest. This could minimize undesirable side effects, which in current therapies frequently affect the whole body, and thus enable more effective treatment of various diseases.

All living organisms rely on sensors to adapt to their environment. One of the most important signals is light, which many organisms perceive using specialized proteins that act as biological switches. This project investigated a family of blue-light-sensitive proteins that control the production of a molecule called cyclic-dimeric-GMP. In nature, this molecule tells bacteria whether to move freely or settle into "biofilms"-stationary communities that are notoriously difficult to treat with antibiotics. Over four years of research, the project team successfully decoded the molecular "logic" of these switches. In the early stages, they discovered that specific protein versions act as incredibly efficient toggles, increasing their enzymatic activity by over 10,000-fold when exposed to light. By studying the physical structure of these proteins, the researchers identified how they "cage" themselves in the dark to stay inactive and how light triggers them to spring open into an active state. The research evolved from studying simple light sensors to more complex "dual-sensor" systems. These sophisticated proteins can process two different signals at once: blue light and chemical markers (phosphorylation). The team discovered that these systems operate using "OR logic," meaning that either light or a chemical signal can independently flip the switch "on". This gives organisms multiple ways to trigger the same biological response depending on the environmental conditions. To achieve these insights, the team utilized modern technologies, including AI-based protein design to predict how mutations change protein behavior and in solution mapping techniques to determine which parts of the proteins move and shift in response to signals. This work has been recognized by the international scientific community, resulting in major publications in journals like Science Advances, Protein Science and the Journal of Biological Chemistry. The ultimate goal of this research is to move beyond observing nature to designing it. By understanding these molecular mechanisms, scientists can create new, non-natural sensors for optogenetics. In the future, this could allow doctors to use localized light to stimulate treatments only at specific sites, such as a tumor, significantly reducing side effects and making treatments more effective. This project has provided parts of the "instruction manual" for how these light-regulated biological machines function, paving the way for new innovations in medicine and biotechnology.