Molecular characterization of unique multi-domain harbouring fungal rhodopsin for establishing their novel opto-synthetic biological usages

Organisms employ light as an external stimulus for regulating cellular functions. The light-sensitive photoreceptors detect light at varying wavelengths, activating signaling cascades and triggering a range of physiological responses. Rhodopsin is a transmembrane heptahelical protein that functions as an ion channel, or a pump, and sensory receptor, respectively. It consists of a light-sensing chromophore, a retinal that upon absorbing light, initiates a series of signaling pathways of sensory perception, growth and survival. Modular rhodopsin (Different from Rhodopsin-Cyclase Module) has been reported in lower eukaryotes, its identification, characterisation and functional significance in the Fungal Kingdom largely unknown. Here, we report the identification of novel modular rhodopsins in fungi, which highlights their potential usages towards the unexplored opto-biotechnological applications (e.g., biomanufacturing of terpenoids, cytoskeleton regulation, DNA metabolism, light-controlled acetyltransferase, etc.) simply by illumination. Furthermore, identification of novel modular rhodopsins augments the expansion of the new optogenetic tools for a wide range of relevant applications. The structural and homology analysis of these identified domains sheds light on their evolutionary lineage and relatedness with the well-characterised bacteriorhodopsin, sensory and channelrhodopsin. The interactome analysis effector domain coupled with the microbial rhodopsin (Rh) reveals RPEL-mediated gene expression and metabolite regulation, which further modulates the retinol synthesis pathway. The role of the fungal Rh-RPEL effector domain in modulating the terpenoid and sphingolipid metabolism in response to light was successfully elucidated via protein-protein interaction and Biosynthesis Gene Cluster (BGC) analysis. This highlights the potential of these novel opto-synthetic biological usages that can induce the light-dependent production of commercially relevant fungal bioactive(s).