Chondroitin 4-O-sulfation regulates hippocampal perineuronal nets and social memory.

Glycan alterations are associated with aging, neuropsychiatric, and neurodegenerative diseases, although the contributions of specific glycan structures to emotion and cognitive functions remain largely unknown. Here, we used a combination of chemistry and neurobiology to show that 4-O-sulfated chondroitin sulfate (CS) polysaccharides are critical regulators of perineuronal nets (PNNs) and synapse development in the mouse hippocampus, thereby affecting anxiety and cognitive abilities such as social memory. Brain-specific deletion of CS 4-O-sulfation in mice increased PNN densities in the area CA2 (cornu ammonis 2), leading to imbalanced excitatory-to-inhibitory synaptic ratios, reduced CREB activation, elevated anxiety, and social memory dysfunction. The impairments in PNN densities, CREB activity, and social memory were recapitulated by selective ablation of CS 4-O-sulfation in the CA2 region during adulthood. Notably, enzymatic pruning of the excess PNNs reduced anxiety levels and restored social memory, while chemical manipulation of CS 4-O-sulfation levels reversibly modulated PNN densities surrounding hippocampal neurons and the balance of excitatory and inhibitory synapses. These findings reveal key roles for CS 4-O-sulfation in adult brain plasticity, social memory, and anxiety regulation, and they suggest that targeting CS 4-O-sulfation may represent a strategy to address neuropsychiatric and neurodegenerative diseases associated with social cognitive dysfunction.

Development of isotope-enriched phosphatidylinositol-4- and 5-phosphate cellular mass spectrometry probes.

Synthetic phosphatidylinositol phosphate (PtdInsP n ) derivatives play a pivotal role in broadening our understanding of PtdInsP n metabolism. However, the development of such tools is reliant on efficient enantioselective and regioselective synthetic strategies. Here we report the development of a divergent synthetic route applicable to the synthesis of deuterated PtdIns4P and PtdIns5P derivatives. The synthetic strategy developed involves a key enzymatic desymmetrisation step using Lipozyme TL-IM®. In addition, we optimised the large-scale synthesis of deuterated myo-inositol, allowing for the preparation of a series of saturated and unsaturated deuterated PtdIns4P and PtdIns5P derivatives. Experiments in MCF7 cells demonstrated that these deuterated probes enable quantification of the corresponding endogenous phospholipids in a cellular setting. Overall, these deuterated probes will be powerful tools to help improve our understanding of the role played by PtdInsP n in physiology and disease.

Photoaffinity Probes for the Identification of Sequence-Specific Glycosaminoglycan-Binding Proteins.

Glycosaminoglycan (GAG)-protein interactions mediate critical physiological and pathological processes, such as neuronal plasticity, development, and viral invasion. However, mapping GAG-protein interaction networks is challenging as these interactions often require specific GAG sulfation patterns and involve transmembrane receptors or extracellular matrix-associated proteins. Here, we report the first GAG polysaccharide-based photoaffinity probes for the system-wide identification of GAG-binding proteins in living cells. A general platform for the modular, efficient assembly of various chondroitin sulfate (CS)-based photoaffinity probes was developed. Systematic evaluations led to benzophenone-containing probes that efficiently and selectively captured known CS-E-binding proteins in vitro and in cells. Importantly, the probes also enabled the identification of >50 new proteins from living neurons that interact with the neuroplasticity-relevant CS-E sulfation motif. Several candidates were independently validated and included membrane receptors important for axon guidance, innate immunity, synapse development, and synaptic plasticity. Overall, our studies provide a powerful approach for mapping GAG-protein interaction networks, revealing new potential functions for these polysaccharides and linking them to diseases such as Alzheimer's and autism.

Engineering transkingdom signalling in plants to control gene expression in rhizosphere bacteria.

The root microbiota is critical for agricultural yield, with growth-promoting bacteria able to solubilise phosphate, produce plant growth hormones, antagonise pathogens and fix N2. Plants control the microorganisms in their immediate environment and this is at least in part through direct selection, the immune system, and interactions with other microorganisms. Considering the importance of the root microbiota for crop yields it is attractive to artificially regulate this environment to optimise agricultural productivity. Towards this aim we express a synthetic pathway for the production of the rhizopine scyllo-inosamine in plants. We demonstrate the production of this bacterial derived signal in both Medicago truncatula and barley and show its perception by rhizosphere bacteria, containing bioluminescent and fluorescent biosensors. This study lays the groundwork for synthetic signalling networks between plants and bacteria, allowing the targeted regulation of bacterial gene expression in the rhizosphere for delivery of useful functions to plants.

Cycloisomerization of allene-enol ethers under Bi(OTf)3 catalysis.

The cycloisomerization of allene-enol ethers under Bi(OTf)3 catalysis was developed as a novel "atom-economic" tool for accessing interesting functionalized cyclopentene rings. Bi(OTf)3 was shown to promote selectively the activation of the enol ether moiety of the substrate. This catalytic methodology was further extended to the synthesis of dihydrofuran and oxaspirocycle derivatives.