title: Identification two novel nacrein-like proteins involved in the shell formation of the Pacific oyster Crassostrea gigas.
abstract: Nacrein-like proteins have carbonic anhydrase (CA)-like domains, but their coding regions are flanked by inserted repeat sequence, such as Gly-X-Asn. Reportedly, nacrein-like proteins show the highest similarity to human carbonic anhydrase 1(α-CA1), possess CA catalytic functions, and play a key role in shell biomineralization. In the present study, two novel nacrein-like proteins were firstly identified from the shell-forming mantle of the Pacific oyster Crassostrea gigas. With numerous analyses, it was identified and characterized that both the nacrein-like proteins F1 and F2 were secreted and most closely related to the nacrein-like protein of California mussel Mytilus californianus via phylogenetic analysis. RT-PCR analysis showed that the nacrein-like proteins F1 and F2 were expressed in multiple tissues and the expression levels remarkably rose after entering the spat stage, which were basically consistent with the increase of calcite fractions in the total shell volume. Surprisingly, the Gly-X-Asn repeat domain, which is distinctive in most nacrein-like proteins, was absent in the two newly identified nacrein-like proteins in C. gigas and replaced with a series of acidic amino acids (D/E). Regardless, nacrein-like proteins in mollusks seem to be vital to the deposition of calcium carbonate and likely perform diverse functions.
authors.affiliation: National & Local Joint Engineering laboratory of Ecological Mariculture, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, Shandong, China.
authors.forename: Xiaorui
authors.initials: X
authors.lastname: Song
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Guofan
authors.initials: G
authors.lastname: Zhang
mesh_terms: D020816:Amino Acid Motifs; D060105:Animal Shells / Q000201:enzymology* / Q000254:growth & development; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D024401:Carbonic Anhydrase I / Q000235:genetics / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D049896:Crassostrea / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D006801:Humans; D008969:Molecular Sequence Data; D049878:Mytilus / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D010140:Pacific Ocean; D010802:Phylogeny; D020033:Protein Isoforms / Q000145:classification / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D020033:Protein Isoforms; D011994:Recombinant Proteins; D024401:Carbonic Anhydrase I; C101387:nacrein; D002256:Carbonic Anhydrases; D002118:Calcium