Natural gums and their derivatives based hydrogels: in biomedical, environment, agriculture, and food industry.

The hydrogels based on natural gums and chemically derivatized natural gums have great interest in pharmaceutical, food, cosmetics, and environmental remediation, due to their: economic viability, sustainability, nontoxicity, biodegradability, and biocompatibility. Since these natural gems are from plants, microorganisms, and seaweeds, they offer a great opportunity to chemically derivatize and modify into novel, innovative biomaterials as scaffolds for tissue engineering and drug delivery. Derivatization improves swelling properties, thereby developing interest in agriculture and separating technologies. This review highlights the work done over the past three and a half decades and the possibility of developing novel materials and technologies in a cost-effective and sustainable manner. This review has compiled various natural gums, their source, chemical composition, and chemically derivatized gums, various methods to synthesize hydrogel, and their applications in biomedical, food and agriculture, textile, cosmetics, water purification, remediation, and separation fields.

Association of autism spectrum disorder with Waardenburg syndrome in a toddler.

Waardenburg syndrome is a rare genetic condition with an incidence of 1 in 212 000. The condition is classically associated with distinctive facial features, congenital hearing loss and pigmentary changes of the hair, iris and skin. There is a paucity of literature about the association of neurodevelopmental conditions with this syndrome. We present a toddler with Waardenburg syndrome type 1 who was referred to our service for developmental delay concerns. The child was diagnosed with the condition at birth, had distinctive facial features, but the hearing was normal. The child's father also shares a similar mutation. Following a multidisciplinary assessment, the child was diagnosed to have autism spectrum disorder with possible regression. We acknowledge that there may not be a causal relationship between autism spectrum and Waardenburg syndrome. However, this highlights the need for developmental surveillance among children diagnosed with Waardenburg syndrome and to consider its association with neurodevelopmental conditions.

Optogenetic modulation of real-time nanoscale dynamics of HCN channels using photoactivated adenylyl cyclases.

Adenosine 3',5'-cyclic monophosphate (cAMP) is a key second messenger that activates several signal transduction pathways in eukaryotic cells. Alteration of basal levels of cAMP is known to activate protein kinases, regulate phosphodiesterases and modulate the activity of ion channels such as Hyper polarization-activated cyclic nucleotide gated channels (HCN). Recent advances in optogenetics have resulted in the availability of novel genetically encoded molecules with the capability to alter cytoplasmic profiles of cAMP with unprecedented spatial and temporal precision. Using single molecule based super-resolution microscopy and different optogenetic modulators of cellular cAMP in both live and fixed cells, we illustrate a novel paradigm to report alteration in nanoscale confinement of ectopically expressed HCN channels. We characterized the efficacy of cAMP generation using ensemble photoactivation of different optogenetic modulators. Then we demonstrate that local modulation of cAMP alters the exchange of membrane bound HCN channels with its nanoenvironment. Additionally, using high density single particle tracking in combination with both acute and chronic optogenetic elevation of cAMP in the cytoplasm, we show that HCN channels are confined to sub 100 nm sized functional domains on the plasma membrane. The nanoscale properties of these domains along with the exchange kinetics of HCN channels in and out of these molecular zones are altered upon temporal changes in the cytoplasmic cAMP. Using HCN2 point mutants and a truncated construct of HCN2 with altered sensitivity to cAMP, we confirmed these alterations in lateral organization of HCN2 to be specific to cAMP binding. Thus, combining these advanced non-invasive paradigms, we report a cAMP dependent ensemble and single particle behavior of HCN channels mediated by its cyclic nucleotide binding domain, opening innovative ways to dissect biochemical pathways at the nanoscale and real-time in living cells.

Biochemical Characterization of the Engineered Soluble Photoactivated Guanylate Cyclases from Microbes Expands Optogenetic Tools.

Cyclic nucleotide, such as cyclic GMP, is a secondary messenger that regulates a wide range of biological process via the diverse signaling cascades. Photoactivated adenylyl cyclases (PACs), constituted of blue light utilizing flavin (BLUF) and cyclase homology domain (CHD), are used as an optogenetic tool to modulate the cyclic AMP (cAMP) level and to study cAMP-mediated signal transduction mechanisms. Here, we have engineered photoactivated adenylyl cyclases (PACs) from microbes to photoactivated guanylyl cyclases (PGCs) via mutagenesis of the substrate binding-specific residues in cyclase homology domain. We demonstrate purification, photodynamic, and detailed biochemical characterization of the engineered PGCs that can serve as optogenetic tool for manipulation of cGMP level in the cells. Engineered PGCs show typical BLUF photoreceptor properties with different recovery kinetics and varying light-regulated guanylyl cyclase activities.

Modulation of cyclic nucleotide-mediated cellular signaling and gene expression using photoactivated adenylyl cyclase as an optogenetic tool.

Cyclic nucleotide signaling pathway plays a significant role in various biological processes such as cell growth, transcription, inflammation, in microbial pathogenesis, etc. Modulation of cyclic nucleotide levels by optogenetic tools has overcome certain limitations of studying transduction cascade by pharmacological agents and has allowed several ways to modulate biological processes in a spatiotemporal manner. Here, we have shown the optogenetic modulation of the cyclooxygenase 2 (Cox-2) gene expression and their downstream effector molecule (PGE2) in HEK-293T cells and the development process of Dictyostelium discoideum via modulating the cyclic nucleotide (cAMP) signaling pathway utilizing photoactivated adenylyl cyclases (PACs) as an optogenetic tool. Light-induced activation of PACs in HEK-293T cells increases the cAMP level that leads to activation of cAMP response element-binding protein (CREB) transcription factor and further upregulates downstream Cox-2 gene expression and their downstream effector molecule prostaglandin E2. In D. discoideum, the light-regulated increase in cAMP level affects the starvation-induced developmental process. These PACs could modulate the cAMP levels in a light-dependent manner and have a potential to control gene expression and their downstream effector molecules with varying magnitude. It would enable one to utilize PAC as a tool to decipher cyclic nucleotide mediated signaling pathway regulations and their mechanism.

Molecular determinant modulates thermal recovery kinetics and structural integrity of the bacterial BLUF photoreceptor.

BLUF domains are flavin-based photoreceptors which receive the blue light signal and are involved in the sensory transduction. We report a short BLUF photoreceptor (SnfB) in Stenotrophomonas sp. We have investigated photodynamic properties of C terminus truncated and several mutated SnfB proteins. Deletion of the extended C-terminal residues alters the thermal recovery kinetics and also affects the integrity of the SnfB protein. Mutagenesis studies demonstrated that the conserved residues within and outside the flavin-binding pocket also regulates the photocycle properties of the protein. These studies suggest that the C-terminal residues outside the BLUF domain can tune the photodynamic properties of the BLUF protein.

Photo-dynamics of photoactivated adenylyl cyclase TpPAC from the spirochete bacterium Turneriella parva strain H(T).

The photoactivated adenylyl cyclase TpPAC from the spirochete bacterium Turneriella parva was synthesized and the purified recombinant protein was characterized by biochemical and optical spectroscopic methods. TpPAC consists of a BLUF domain (BLUF = Blue Light sensor Using Flavin) and an adenylyl cyclase homology domain (CHD). A light induced cAMP cyclase activity of ≈ 53.3 nmolmg(-1)min(-1) was measured while in the dark the cyclase activity was approximately a factor of 240 lower. The photo-cycling dynamics of the BLUF domain of TpPAC was studied by absorption spectra, fluorescence quantum distribution, and fluorescence lifetime measurements. The quantum efficiency of BLUF domain signaling state formation was found to be ϕs ≈ 0.59. A three-component exponential recovery of the signaling state to the receptor state was observed with the time constants τrec,1 = 4.8s, τrec,2 = 34.2s, and τrec,3 = 293s at 21.3 °C. The protein thermal stability was studied by stepwise sample heating and cooling. An apparent TpPAC melting temperature of ϑm ≈ 46 °C was determined. The photo-degradation of TpPAC in the signaling state was studied by prolonged intense light exposure at 455 nm. An irreversible flavin photo-degradation was observed with quantum yield ϕD ≈ 8.7 × 10(-6).

Bacteriophytochrome controls carotenoid-independent response to photodynamic stress in a non-photosynthetic rhizobacterium, Azospirillum brasilense Sp7.

Ever since the discovery of the role of bacteriophytochrome (BphP) in inducing carotenoid synthesis in Deinococcus radiodurans in response to light the role of BphPs in other non-photosynthetic bacteria is not clear yet. Azospirillum brasilense, a non-photosynthetic rhizobacterium, harbours a pair of BphPs out of which AbBphP1 is a homolog of AtBphP1 of Agrobacterium tumefaciens. By overexpression, purification, biochemical and spectral characterization we have shown that AbBphP1 is a photochromic bacteriophytochrome. Phenotypic study of the ΔAbBphP1 mutant showed that it is required for the survival of A. brasilense on minimal medium under red light. The mutant also showed reduced chemotaxis towards dicarboxylates and increased sensitivity to the photooxidative stress. Unlike D. radiodurans, AbBphP1 was not involved in controlling carotenoid synthesis. Proteome analysis of the ΔAbBphP1 indicated that AbBphP1 is involved in inducing a cellular response that enables A. brasilense in regenerating proteins that might be damaged due to photodynamic stress.