Elucidating the functional domain architecture of ArCS1, a biomineralizing myosin chitin synthase: I. The role of lipids

In molluscs, chitin synthases play a crucial role in biomineralization, and certain variants have a myosin motor domain that could connect polymer synthesis with the cytoskeleton. To investigate ArCS1_E22TM, researchers developed a reproducible method for expressing it in Dictyostelium discoideum and refined the lipid composition to MSP1D1deltaH5 (POPC:POPE:POPG 3:1:1) with 20% cholesterol.

This resulted in uniform nanodiscs with a diameter of approximately 8.2 nm. By analyzing the full-length ArCS1 and its subdomains with AlphaFold3, scientists found that the myosin motor, glycosyltransferase, and transmembrane regions are well-defined but loosely connected, implying flexible linking and conformational coupling. The study also used Mg2+ and oleic acid as ligands in structural modeling and compared it to bacterial cellulose synthase and yeast chitin synthase 1 to understand substrate binding and a possible mechanism for chitin polymerization and translocation.

This work establishes a standard protocol for detailed structural assessments of recombinant molluscan chitin synthase in near-native or biomimetic membranes, paving the way for high-resolution cryo-electron microscopy to resolve the first experimentally observed structure of a molluscan chitin synthase and shed light on its structural architecture and regulatory mechanisms of biomineralization.