The <em>MUC2 </em>Gene Product: Polymerisation and Post-Secretory Organisation—Current Models

\ua9 2024 by the authors.MUC2 mucin, the primary gel-forming component of intestinal mucus, is well researched and a model of polymerisation and post-secretory organisation has been published previously. Recently, several significant developments have been made which either introduce new ideas or challenge previous theories. New ideas include an overhaul of the MUC2 C-terminal globular structure which is proposed to harbour several previously unobserved domains, and include a site for an extra intermolecular disulphide bridge dimer between the cysteine 4379 of adjacent MUC2 C-termini. MUC2 polymers are also now thought to be secreted attached to the epithelial surface of goblet cells in the small intestine and removed following secretion via a metalloprotease meprin β-mediated cleavage of the von Willebrand D2 domain of the N-terminus. It remains unclear whether MUC2 forms intermolecular dimers, trimers, or both, at the N-termini during polymerisation, with several articles supporting either trimer or dimer formation. The presence of a firm inner mucus layer in the small intestine is similarly unclear. Considering this recent research, this review proposes an update to the previous model of MUC2 polymerisation and secretion, considers conflicting theories and data, and highlights the importance of this research to the understanding of MUC2 mucus layers in health and disease

Factors affecting capacity and voltage fading in disordered rocksalt cathodes for lithium-ion batteries

Disordered rocksalt cathodes deliver high energy densities, but they suffer from pronounced capacity and voltage fade on cycling. Here, we investigate fade using two disordered rocksalt lithium manganese oxyfluorides: Li3Mn2O3F2 (Li1.2Mn0.8O1.2F0.8), which stores charge by Mn2+/Mn4+ redox, and Li2MnO2F, where charge storage involves both Mn3+/Mn4+ and oxygen redox (O-redox). Li3Mn2O3F2 is reported for the first time. We identify the growth of an electronically resistive surface layer with cycling that is present in both Li2MnO2F and Li3Mn2O3F2 but more pronounced in the presence of O-redox. This resistive surface inhibits electronic contact between particles, leading to the observed voltage polarization and capacity loss. By increasing carbon loading in the composite cathode, it is possible to substantially improve the cycling performance. These results help to disentangle O-redox from other leading causes of capacity fading in Mn oxyfluorides and highlight the importance of maintaining electronic conductivity in improving capacity and voltage retention