Abstract
The mussel shell protein 22.8 (MSP22.8) is recognized by a monoclonal antibody (M22.8) directed against larvae of the mussel Mytilus galloprovincialis. After being secreted by cells of the mantle‐edge epithelium into the extrapallial (EP) space (the gap between the mantle and the shell), the protein is detected in the extrapallial fluid (EPF) and EP hemocytes and finally becomes part of the shell matrix framework in adult specimens of M. galloprovincialis. In the work described here, we show how MSP22.8 is detected in EPF samples from different species of mussels (M. galloprovincialis, Mytilus edulis, and Xenostrobus securis), and also as a shell matrix protein in M. galloprovincialis, Mytilus chilensis, and Perna canaliculus. A multistep purification strategy was employed to isolate the protein from the EPF, which was then analyzed by mass spectrometry in order to identify it. The results indicate that MSP22.8 is a serpin‐like protein that has great similarity with the protease inhibitor‐like protein‐B1, reported previously for Mytilus coruscus. We suggest that MSP22.8 is part of a system offering protection from proteolysis during biomineralization and is also part of the innate immune system in mussels.
Highlights
The mussel shell protein 22.8 (MSP22.8) is recognized by a monoclonal antibody (M22.8) directed against larvae of the mussel Mytilus galloprovincialis
We described the generation of the monoclonal antibody M22.8 [20,21] directed against Mytilus galloprovincialis larvae, which recognizes an antigen referred to as mussel shell protein 22.8 (MSP22.8) [22]
We showed how MSP22.8 is detected in EP-resident hemocytes, but not in those from the hemolymph, and that hemocytes have the capability to take up the protein, with the MSP22.8 antigen being detected as a shell matrix protein [22]
Summary
The mussel shell protein 22.8 (MSP22.8) is recognized by a monoclonal antibody (M22.8) directed against larvae of the mussel Mytilus galloprovincialis. Some authors defend the idea of juxtaposition of mantle cells that suggests a narrow contact between mantle cells and the mineralization site [5,7,8] In this scenario, there is no clear function for the extrapallial fluid (EPF). EPF is believed to play a major role in shell formation, there are very few studies that focus on this particular liquid or its proteins [9,10]. Most of these studies only concern the inorganic composition [11,12,13] or the macromolecules [14,15,16]. Abbreviations ECM, extracellular matrix; EMs, electron micrographs; FA, focal adhesion; FAK, focal adhesion kinase; GEFs, guanine nucleotide exchange factors; iPALM, interferometric photoactivated localization microscopy; IRM, interference reflection microscopy
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