Dual Roles of the Lysine-Rich Matrix Protein (KRMP)-3 in Shell Formation of Pearl Oyster, Pinctada fucata

PLoS One. 2015 Jul 10;10(7):e0131868. doi: 10.1371/journal.pone.0131868. eCollection 2015.

Abstract

Matrix proteins play important roles in shell formation. Our group firstly isolated three cDNAs encoding lysine-rich matrix protein from Pinctada fucata in 2006. However, the functions of KRMPs are not fully understood. In addition, KRMPs contain two functional domains, the basic domain and the Gly/Tyr domain respectively. Based on the modular organization, the roles of their two domains were poorly characterized. Furthermore, KRMPs were then reported in other two species, P. maxima and P. margaritifera, which indicated that KRMPs might be very important for shell formation. In this study, the characterization and function of KRMP-3 and its two functional domains were studied in vitro through purification of recombinant glutathione S-transferase tagged KRMP-3 and two KRMP-3 deletion mutants. Western blot and immunofluorescence revealed that native KRMP-3 existed in the EDTA-insoluble matrix of the prismatic layer and was located in the organic sheet and the prismatic sheath. Recombinant KRMP-3 (rKRMP-3) bound tightly to chitin and this binding capacity was duo to the Gly/Tyr-rich region. rKRMP-3 inhibited the precipitation of CaCO3, affected the crystal morphology of calcite and inhibited the growth of aragonite in vitro, which was almost entirely attributed to the lysine-rich region. The results present direct evidence of the roles of KRMP-3 in shell biomineralization. The functional rBR region was found to participate in the growth control of crystals and the rGYR region was responsible to bind to chitin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animal Shells / growth & development
  • Animal Shells / metabolism*
  • Animals
  • Calcium Carbonate / chemistry
  • Chemical Precipitation
  • Chitin / metabolism
  • Conserved Sequence
  • Crystallization
  • Extracellular Matrix Proteins / chemistry
  • Extracellular Matrix Proteins / physiology*
  • Molecular Sequence Data
  • Pinctada / growth & development
  • Pinctada / metabolism*
  • Protein Binding
  • Protein Transport
  • Sequence Homology, Amino Acid

Substances

  • Extracellular Matrix Proteins
  • Chitin
  • Calcium Carbonate

Grants and funding

This work was supported by the National Natural Science Foundation of China Grants 31372502, 31172382 and Independent Research Projects of Tsinghua University Grant 20111080964.