MSP22.8 is a protease inhibitor-like protein involved in shell mineralization in the edible mussel Mytilus galloprovincialis

MSP22.8 is a shell matrix protein described in Mytilus galloprovincialis. During the characterization of the monoclonal antibody M22.8, we have demostrated that MSP22.8 is secreted into the extrapallial space by cells of the mantle edge epithelium. The protein is detected in the extrapallial fluid and extrapallial hemocytes and finally becomes part of the shell matrix framework. In order to isolate the protein from the extrapallial fluid, a multi-step purification strategy was designed, involving ammonium sulfate precipitation followed by affinity or size-exclusion chromatography. Eluted fractions were further processed by SDS-PAGE or 2D-PAGE. Positivity of fractions, bands and spots were checked by Western or Dot blot. Positive bands and spots were manually excised and sent for mass spectrometry experiments for protein identification.