A crustacean Ca2+-binding protein with a glutamate-rich sequence promotes CaCO3 crystallization.
The DD4 mRNA of the penaeid prawn Penaeus japonicus was shown previously to be expressed in the epidermis adjacent to the exoskeleton specifically during the post-moult period, when calcification of the exoskeleton took place. The encoded protein possessed a Ca2+-binding site, suggesting its involvement in the calcification of the exoskeleton. In the present study, an additional ORF (open reading frame) of 289 amino acids was identified at the 5' end of the previous ORF. The newly identified part of the encoded protein included a region of approx. 120 amino acids that was highly rich in glutamate residues, and contained one or more Ca2+-binding sites. In an immunohistochemical study, signals were detected within calcified regions in the endocuticular layer of the exoskeleton. Bacterially expressed partial segments of the protein induced CaCO3 crystallization in vitro. Finally, a reverse transcription-PCR study showed that the expression was limited to an early part of the post-moult period, preceding significant calcification of the exoskeleton. These observations argue for the possibility that the encoded protein, renamed crustocalcin (CCN), promotes formation of CaCO3 crystals in the exoskeleton by inducing nucleation.
Endo
Hirotoshi
H
Department of Marine Bioscience, Ocean Research Institute, The University of Tokyo, Tokyo, Japan.
Takagi
Yasuaki
Y
Ozaki
Noriaki
N
Kogure
Toshihiro
T
Watanabe
Toshiki
T
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D015153:Blotting, Western / Q000379:methods; D002113:Calcification, Physiologic / Q000502:physiology*; D002119:Calcium Carbonate / Q000378:metabolism*; D002132:Calcium Radioisotopes / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D018076:DNA, Complementary / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D008969:Molecular Sequence Data; D008970:Molecular Weight; D021141:Nucleic Acid Amplification Techniques / Q000379:methods; D016366:Open Reading Frames / Q000235:genetics; D033561:Penaeidae / Q000033:anatomy & histology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
D002132:Calcium Radioisotopes; D002135:Calcium-Binding Proteins; C414586:DD4 protein, Penaeus japonicus; D018076:DNA, Complementary; D018698:Glutamic Acid; D002119:Calcium Carbonate