Mucociliary defense, mediated by the ciliated and goblet cells, is fundamental to respiratory fitness. The concerted action of ciliary movement on the respiratory epithelial surface and the pathogen entrapment function of mucus help to maintain healthy airways. Consequently, genetic or acquired defects in lung defense elicit respiratory diseases and secondary microbial infections that inflict damage on pulmonary function and may even be fatal. Individuals living with chronic and acute respiratory diseases are more susceptible to develop severe coronavirus disease-19 (COVID-19) illness and hence should be proficiently managed. In light of the prevailing pandemic, we review the current understanding of the respiratory system and its molecular components with a major focus on the pathophysiology arising due to collapsed respiratory epithelium integrity such as abnormal ciliary movement, cilia loss and dysfunction, ciliated cell destruction, and changes in mucus rheology. The review includes protein interaction networks of coronavirus infection-manifested implications on the molecular machinery that regulates mucociliary clearance. We also provide an insight into the alteration of the transcriptional networks of genes in the nasopharynx associated with the mucociliary clearance apparatus in humans upon infection by severe acute respiratory syndrome coronavirus-2.

Light-gated ion channel and ion pump rhodopsins are widely used as optogenetic tools and these can control the electrically excitable cells as (1) they are a single-component system i.e., their light sensing and ion-conducting functions are encoded by the 7-transmembrane domains and, (2) they show fast kinetics with small dark-thermal recovery time. In cellular signaling, a signal receptor, modulator, and the effector components are involved in attaining synchronous regulation of signaling. Optical modulation of the multicomponent network requires either receptor to effector encoded in a single ORF or direct modulation of the effector domain through bypassing all upstream players. Recently discovered modular rhodopsins like rhodopsin guanylate cyclase (RhoGC) and rhodopsin phosphodiesterase (RhoPDE) paves the way to establish a proof of concept for utilization of complex rhodopsin (modular rhodopsin) for optogenetic applications. Light sensor coupled modular system could be expressed in any cell type and hence holds great potential in the advancement of optogenetics 2.0 which would enable manipulating the entire relevant cell signaling system. Here, we had identified 50 novel modular rhodopsins with variant domains and their diverse cognate signaling cascades encoded in a single ORF, which are associated with specialized functions in the cells. These novel modular algal rhodopsins have been characterized based on their sequence and structural homology with previously reported rhodopsins. The presented novel modular rhodopsins with various effector domains leverage the potential to expand the optogenetic tool kit to regulate various cellular signaling pathways across the diverse biological model systems.

Organisms can respond to varying light conditions using a wide range of sensory photoreceptors. These photoreceptors can be standalone proteins or represent a module in multidomain proteins, where one or more modules sense light as an input signal which is converted into an output response via structural rearrangements in these receptors. The output signals are utilized downstream by effector proteins or multiprotein clusters to modulate their activity, which could further affect specific interactions, gene regulation or enzymatic catalysis. The blue-light using flavin (BLUF) photosensory module is an autonomous unit that is naturally distributed among functionally distinct proteins. In this study, we identified 34 BLUF photoreceptors of prokaryotic and eukaryotic origin from available bioinformatics sequence databases. Interestingly, our analysis shows diverse BLUF-effector arrangements with a functional association that was previously unknown or thought to be rare among the BLUF class of sensory proteins, such as endonucleases, tet repressor family (tetR), regulators of G-protein signaling, GAL4 transcription family and several other previously unidentified effectors, such as RhoGEF, Phosphatidyl-Ethanolamine Binding protein (PBP), ankyrin and leucine-rich repeats. Interaction studies and the indexing of BLUF domains further show the diversity of BLUF-effector combinations. These diverse modular architectures highlight how the organism’s behaviour, cellular processes, and distinct cellular outputs are regulated by integrating BLUF sensing modules in combination with a plethora of diverse signatures. Our analysis highlights the modular diversity of BLUF containing proteins and opens the possibility of creating a rational design of novel functional chimeras using a BLUF architecture with relevant cellular effectors. Thus, the BLUF domain could be a potential candidate for the development of powerful novel optogenetic tools for its application in modulating diverse cell signaling.

In bacteria, cyclic adenosine monophosphate (cAMP) signaling plays an essential regulatory role whose modulation via optogenetic tools would provide researchers an immense opportunity to control biological processes simply by illumination. The cAMP signaling in bacteria is a complex network of regulatory pathways, which utilizes distinct proteomic resources under different nutrient environments. We established an optogenetic modulation of cAMP and studied important cellular process of growth, biofilm formation, and virulence in the model bacterium E. coli using a light-gated adenylate cyclase (LgAC) from Beggiatoa sp. Blue light-induced activation of LgAC elevated the cAMP level in a blue light-dependent manner in E. coli. Quantitative proteomics revealed a decrease in the level of certain proteins governing growth (PTS, Adk, AckA, GlnA, and EFP), biofilm formation (IhfA, flagellin, YajQ, YeaG, and HlfC), and virulence (ClpP, YebC, KatE, BtuE, and Zur) in E. coli cells expressing LgAC upon blue light illumination. This optogenetic modulation of cAMP would be useful for deciphering cAMP-associated host–pathogen signaling of bacterial systems. Proteome knowledge established by this research work would also be useful for the scientific community while adapting LgAC-based optogenetic modulation for studying other relevant cAMP-driven bacterial physiology (e.g., energy metabolism). The systematic utilization of the established method and more extensively designed experiments regarding bacterial growth, biofilm, survival, and virulence might provide a road map for the identification of new targets for developing novel antibacterial drugs.

Light-gated ion channel and ion pump rhodopsins are widely used as optogenetic tools and these can control the electrically excitable cells as: (1) they are a single-component system i.e., their sensor and effector functions are encoded by the 7-transmembrane domains and (2) they show fast kinetics with small dark-thermal recovery time. In cellular signaling, a signal receptor, modulator and effector components are involved for attaining synchronous multicomponent regulation. Optical modulation of this network requires either receptor to effector encoded in a single ORF or direct modulation of the effector domain through bypassing all upstream players. Recently discovered modular rhodopsins like rhodopsin guanine cyclase (RhoGC) and rhodopsin phosphodiesterase (RhoPDE) paves the way to establish proof of concept. Light sensor coupled modular system could be expressed in a precise cell type and which holds great potential in the advancement of optogenetics 2.0. It would enable manipulating entire relevant cell signaling system. Here, we had identified 50 novels modular rhodopsins with variant rhodopsins domain and its diverse cognate signaling cascades encoded in a single ORF, which are associated with specialized functions in the cells. These novel modular algal rhodopsins have been characterized functionality based on their sequence and structural homology with previously characterized rhodopsins. Presented novel modular rhodopsins with various effector domains hold potential to expand optogenetics tool kit to regulate various cellular signaling pathways across the diverse biological model systems.