Signal Integration in Phytochrome-linked PPM-phosphatases

Nature has developed an astonishingly modular architecture of covalently linked protein domains during evolution. The use of diverse building blocks has enabled organisms to develop complex cellular networks that are critical for cell survival. The frequently observed coupling of sensory modules with enzymatic effectors allows direct regulation of, for example, cellular adaptations in response to diverse stimuli. From the many different sensory signals, light an almost omnipresent external stimulus can be sensed by specific photoreceptor proteins and thereby regulate specific signalling cascades within diverse organisms. Well known examples of such processes include the circadian rhythm and the shade avoidance response of plants. The interest in such light-controlled systems is not limited to naturally occurring regulation mechanisms. It has grown substantially with the advent of optogenetics, which refers to the concept of genetically manipulating biological systems to enable optical control of cellular processes. However, the need for light-driven systems goes beyond naturally occurring photoreceptors. Although progress has been made in understanding the concepts of light activation, the rational design of synthetic tools is still challenging. In particular, since mechanistic descriptions of light signalling differ within photoreceptor families and tend to be dominated by the specific output domains, a more detailed understanding of sensor-effector modularity is required. As part of this research project, we will conduct a detailed study of red light sensors linked to metal-dependent phosphatases (PPMs). This will include naturally occurring systems as well as artificial light-regulatable variants designed to probe mechanistic concepts of signal transduction. By identifying key signalling elements, we will gain valuable insight into the modular coupling of sensors and effectors, a concept frequently often observed in nature. We will use an interdisciplinary approach combining biochemistry with biophysics and structural biology to characterise these systems. We will use atomic models obtained by crystallography and cryo-EM and functionally extended them by in-solution studies addressing the dynamics of these systems. The combined results will strengthen our understanding of light signal transduction on a molecular level from both the photoreceptor and effector domain. This will give us a better understanding of the modularity observed in natural light-regulated systems and support a more rational design of artificial optogenetic tools. PPM phosphatases are particularly attractive pharmacological targets because their hyperactivation/dysfunction is associated with a number of diseases including cancer. Specifically designed red light-regulatable PPMs for physiologically relevant targets will undoubtedly be valuable tools for future therapeutic developments.