s-Afadin binds to MAGUIN/Cnksr2 and regulates the localization of the AMPA receptor and glutamatergic synaptic response in hippocampal neurons

A hippocampal mossy fiber synapse implicated in learning and memory is a complex structure in which a presynaptic bouton attaches to the dendritic trunk by puncta adherentia junctions (PAJs) and wraps multiply branched spines. The postsynaptic densities (PSDs) are localized at the heads of each of these spines and faces to the presynaptic active zones. We previously showed that the scaffolding protein afadin regulates the formation of the PAJs, PSDs, and active zones in the mossy fiber synapse. Afadin has two splice variants: l-afadin and s-afadin. l-Afadin, but not s-afadin, regulates the formation of the PAJs but the roles of s-afadin in synaptogenesis remain unknown. We found here that s-afadin more preferentially bound to MAGUIN (a product of the Cnksr2 gene) than l-afadin in vivo and in vitro. MAGUIN/CNKSR2 is one of the causative genes for nonsyndromic X-linked intellectual disability accompanied by epilepsy and aphasia. Genetic ablation of MAGUIN impaired PSD-95 localization and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) receptor surface accumulation in cultured hippocampal neurons. Our electrophysiological analysis revealed that the postsynaptic response to glutamate, but not its release from the presynapse, was impaired in the MAGUIN-deficient cultured hippocampal neurons. Furthermore, disruption of MAGUIN did not increase the seizure susceptibility to flurothyl, a GABA_A receptor antagonist. These results indicate that s-afadin binds to MAGUIN and regulates the PSD-95-dependent cell surface localization of the AMPA receptor and glutamatergic synaptic responses in the hippocampal neurons and that MAGUIN is not involved in the induction of epileptic seizure by flurothyl in our mouse model.

Microbial system for polysaccharide depolymerization: enzymatic route for gellan depolymerization by Bacillus sp. GL1

A bacterium-producing polysaccharide lyase (gellan lyase) was isolated from soil samples and identified to be Bacillus sp. The lyase was purified from the culture fluid of the bacterium (designated Bacillus sp. GL1) grown in the presence of gellan as a carbon source. The purified gellan lyase depolymerized deacetylated gellan and gave a single oligosaccharide product with a molecular weight of 646, which was determined by fast atom bombardment mass spectrometry. The structure of the product was determined by the combination of mass spectrometry, HPLC analysis, and high-resolution proton nuclear magnetic resonance spectroscopy to be a tetrasaccharide of glucuronyl-glucosyl-rhamnosyl-glucose with unsaturated glucuronic acid at the nonreducing terminal. When incubated in cell extracts of Bacillus sp. GL1, the tetrasaccharide was first converted to trisaccharide without unsaturated glucuronyl residue, and the trisaccharide was then converted to hydrolyzed monosaccharides glucose and rhamnose. These results show that, in the bacterium Bacillus sp. GL1, gellan is first depolymerized to give a tetrasaccharide, a repeating unit in gellan molecule, by an extracellular gellan lyase and then the tetrasaccharide is hydrolyzed to monosaccharides by successive actions of intracellular exoglycosidases.