Recombinant transgelin‐like protein 1 from Mytilus shell induces formation of CaCO(3) polymorphic crystals in vitro

Transgelin is an actin cross‐linking/gelling protein of the calponin family, which is associated with actin stress fibres, cell motility, adhesion and the maintenance of cell morphology. Transgelin‐like proteins (TLPs) have also been identified as shell matrix proteins (SMPs) in several mollusc species; however, the functions of TLPs in biomineralization remain unknown. Transgelin‐like protein 1 (TLP‐1) was previously identified from the shell of Mytilus coruscus as a novel 19 kDa SMP with a calponin homology (CH) domain. To understand the role of TLP‐1 in shell formation, the expression level and localization of the TLP‐1 gene in biomineralization‐related tissues were determined in this study. Furthermore, recombinant TLP‐1 was expressed in a prokaryotic expression system with codon optimization, and an anti‐rTLP‐1 antibody was prepared based on the expressed recombinant TLP‐1 (rTLP‐1) protein. In vitro, rTLP‐1 induced the formation of CaCO(3) polymorphic crystals with distinct morphologies and inhibited crystallization rate and crystal interactions. Immunohistochemical, immunofluorescence, and pull‐down analyses using the anti‐rTLP‐1 antibody revealed the specific locations of TLP‐1 in biomineralization‐related tissues and shell myostracum layer, and suggested the existence of a possible TLP‐1 interaction network in the shell matrix. Our results are beneficial for understanding the functions of TLP‐1, particularly through its CH domain, during shell mineralization.