Transmembrane myosin chitin synthase involved in mollusc shell formation produced in Dictyostelium is active

Several mollusc shells contain chitin, which is formed by a transmembrane myosin motor enzyme. This protein could be involved in sensing mechanical and structural changes of the forming, mineralizing extracellular matrix. Here we report the heterologous expression of the transmembrane myosin chitin synthase Ar-CS1 of the bivalve mollusc Atrina rigida (2286 amino acid residues, M.W. 264 kDa/monomer) in Dictyostelium discoideum, a model organism for myosin motor proteins. Confocal laser scanning immunofluorescence microscopy (CLSM), chitin binding GFP detection of chitin on cells and released to the cell culture medium, and a radiochemical activity assay of membrane extracts revealed expression and enzymatic activity of the mollusc chitin synthase in transgenic slime mold cells. First high-resolution atomic force microscopy (AFM) images of Ar-CS1 transformed cellulose synthase deficient D. discoideumdcsA− cell lines are shown.

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► Dictyostelium produces the 264 kDa myosin chitin synthase of bivalve mollusc Atrina.
► Chitin synthase activity releases chitin, partly associated with the cell surface.
► Membrane extracts of transgenic slime molds produce radiolabeled chitin in vitro.
► Chitin producing Dictyostelium cells can be characterized by atomic force microscopy.
► This model system enables us to study initial processes of chitin biomineralization.