Development of novel red light responsive optogenetic tools using the truncated IsPadC protein as template

Pivotal to many life forms on earth is integrating and reacting accordingly to differences in light conditions. Therefore, a plethora of proteinaceous systems dynamically tuned by interacting with light arouse in different life forms like bacteria, fungi and plants etc [1].
A subgroup of bacteriophytochromes comprise the so-called PadCs (phytochrome-activated diguanylate cyclases). Typical for these phytochromes, a modular system can be observed as shown below. The Photosensory module (PSM, in violet, blue, green) integrates red light stimulation via its covalently linked biliverdin IXα chromophore [2,3]. This light input is then translated into the fine tuned production of c-di-GMP by the output domain (red) which serves as bacterial second messenger [4].
Recently, the research field of optogenetics (see box on the right) showed an ever increasing drive to discover new phytochromes with improved light integration and output signal properties. Red light stimulated proteins are especially well suited in these endeavours because this wavelength range can penetrate biological tissue with minimal signal attenuation [2].
In a recent study by Buhrke et al. [5] a truncated version of the red light stimulated protein IsPadC showed interesting altered dimerization properties while keeping its beneficial spectral characteristics. This might allow the development of new improved optogentic tools.