Calreticulin is a unique calcium-binding protein with multiple functions mostly located in the sarcoplasmic/endoplasmic reticulum. A large amount of calcium is absorbed from the medium and transported to mineralization sites during biomineralization in pearl oyster. This paper describes the cloning of the full-length cDNA of calreticulin from Pinctada fucata, namely PCRT. PCRT encodes a deduced 414-amino acid protein, which includes a predicted 17-amino acid signal peptide and an endoplasmic reticulum retrieval sequence HDEL. The protein shows 63%-76% sequence identity and shares some common characteristics with calreticulins from other species. Semi-quantitative RT-PCR indicates that PCRT is ubiquitously expressed in all tissues tested with the highest expression in the hemolymph and the mantle. In situ hybridization analysis of PCRT in the mantle showed strong signals in the inner fold, the inner side of middle fold, and the inner side of outer fold of the mantle epithelium. All these results suggest PCRT might be involved in Ca²⁺ transport and storage during oyster biomineralization.

In oyster biomineralization, large amounts of calcium are absorbed from external media, transported to the mineralization site, and finally deposited via a matrix-mediated process. All these activities are very energy intensive; therefore, investigations of the energy metabolism pathways of different oyster tissues will facilitate understanding of oyster biomineralization physiology. A full-length cDNA encoding the F₁-ATPase beta-subunit (the F₁-β-subunit, a major calalytic subunit of F-ATPase) from the pearl oyster (Pinctada fucata) was cloned using the homology strategy with a pair of degenerated primers based on the conserved regions of other animals' F₁-β-subunit genes. Sequencing and structural analyses showed that the obtained sequence shared high identity with other animals' F₁-β-subunits, and had a unique phosphorylation site of PKC and CK II on the external surface of the putative protein. Results from semi-quantitative reverse transcription-polymerase chain reaction and in situ hybridization demonstrated this oyster F₁-β-subunit mRNA is abundant in the gill and mantle, and distributed widely in the periostracal groove, the outer folder, and the dorsal region of the mantle and in the gill epithelial cells. These tissues were the main regions that participate in biomineralization processes such as calcium uptake, transport, and matrix secretion. The results indicate that tissues involved in biomineralization have stronger energy metabolic processes and that F₁-ATPase might play an important role in oyster biomineralization by providing energy transport.

Mitochondrial ATP synthase is responsible for the production of the majority of the cellular ATP, which is composed of two major units: F₀ and F₁. Although much is known about the active complex (5 subunits (αβγδε)), the role of the α subunit in the catalytic mechanism remains unclear, particularly in bivalve animals. This study first cloned and identified the full-length sequence of the mitochondrial H⁺-ATP synthase α subunit cDNA gene in Pinctada fucata using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. The Pinctada fucata mitochondrial H⁺-ATP synthase α subunit contains 1991 nucleotides, with the translation start site at nt 48 (ATG) and the stop codon at nt 1660 (TAA), encoding a polypeptide 553 amino acids in length, which shares high similarity to that of other animals (81% identity to fruit fly, 82% to carp, and 83% to humans). Alignment analysis of the well-conserved amino acid domains in the ATPase α subunit, the α/β signal transduction domain, showed that two residues (Asp³⁵⁸ and Asn³⁵⁹) differ from any other ATP synthase α subunit. In situ hybridization analysis was used to reveal the wide-spread distribution of mitochondrial H⁺-ATP synthase in various tissues in Pinctada fucata. This work will help further research on pearl energy metabolism to increase the output and quality of pearls to more efficiently utilize our rich pearl oyster resources.

The effects of genistein on several tumor cell lines were investigated to study the effects of genistein on cell growth, cell cycle, and apoptosis of two murine melanoma cell lines, B16 and K1735M2. These two closely related murine melanoma cell lines, however, have different responses to the genistein treatment. Genistein inhibits the growth of both the B16 and K1735M2 cell lines and arrests the growth at the G2/M phase. After treatment with 60 µmol/L genistein for 72 h, apoptosis and caspase activities were detected in B16 cells, while such effects were not found in K1735M2. Further tests showed that after genistein treatment the protein content and mRNA levels of p53 increased in B16, but remained the same in K1735M2. The protein content and mRNA levels of p21^WAF1/CIP1 increased in both cell lines after treatment. The results show that genistein might induce apoptosis in B16 cells by damaging the DNA, inhibiting topoisomerase II, increasing p53 expression, releasing cytochrome c from the mitochondria, and activating the caspases which will lead to apoptosis.

Many of the effects of Ca²⁺ signaling are mediated through the Ca²⁺/calmodulin complex and its acceptors, the Ca²⁺/calmodulin-dependent protein kinases, including PSKH1. Studies of the proteins involved in the calcium metabolism in oysters will help elucidate the pearl formation mechanism. This paper describes a full-length PSKH1 cDNA isolated from pearl oyster Pinctada fucata. Oyster PSKH1 shares 65% homology with human PSKH1 and 48% similarity with rat CaM kinase I in the amino acid sequence, and contains a calmodulin-binding domain. The results of semi-quantitative reverse transcription-polymerase chain reaction and in situ hybridization revealed that oyster PSKH1 mRNA is highly expressed in the outer epithelial cells of the mantle pallial and in the gill epithelial cells. These studies provide important information describing the complex Ca²⁺ signaling mechanism in oyster calcium metabolism.

A soluble matrix protein P14 with an apparent molecular mass of 14.5 kDa was isolated from fragmented nacre of pearl oysters (Pinctada fucata) treated with 10% NaOH solution to investigate the nacre matrix proteins and their effect on the CaCO₃ crystal. The protein was characterized by gel exclusion chromatography and reversed-phase high performance liquid chromatography after demineralization by 10% acetic acid. The X-ray diffraction pattern of P14 crystals indicates that P14 plays an important role in nacre biomineralization. P14 can induce aragonite formation, stimulate CaCO₃ crystal formation, and accelerate aragonite precipitation. Heating of the acid insoluble nacre residue, which was named conchiolin, in 10% sodium dodecyl sulfate solution supplemented with 10% β-mercaptoethanol solution for 10-20 min at about 100°C gave two other soluble proteins having molecular masses of 19.4 kDa and 25.0 kDa. The present study suggests that these two proteins are linked to the insoluble organic matrix by disulfide bridges because the extraction yield increases when β-mercaptoethanol is added to the medium.

Equilibrium guanidinium chloride (GdmCl)-induced unfolding of arginine kinase (AK) was investigated by enzymatic activity, intrinsic fluorescence, 8-anilinonaphthalene-1-sulfonic acid (ANS) fluorescence, circular dichroism (CD) spectrum, and size-exclusion chromatography. The measurements showed that AK unfolded through two equilibrium intermediates: the molten globule state and the partly folded state. Both intermediates have no enzyme activity. The molten globule state exists at 0.4-0.8 mol/L GdmCl, perhaps after the N-terminal domain has unfolded but the C-terminal domain is still intact. The partly folded state occurs at 1.1-1.5 mol/L GdmCl with a hydrodynamic volume no more than 1.6-fold larger than the native state and a pronounced far UV-CD signal. Its ANS fluorescence intensity is about 50% of the molten globule state. This partly folded state shares similarities with the “burst” kinetic intermediate of protein folding.

Alkaline phosphatase from Pinctada fucata was inactivated by o-phthalaldehyde (OPA). The inactivation followed pseudo first-order kinetics with a second rate constant of 0.167 (mmol/L)^-1 ·min^-1 at pH 7.5 and 25℃. A Tsou's plot analysis showed that inactivation occurred upon formation of one isoindole group. The OPA-modified enzyme lost the ability to bind with the specific affinity column and the presence of substrates or competitive inhibitors protected the enzyme from inactivation. The results revealed that the OPA-reaction site was at the enzyme substrate binding site. Prior modification of the enzyme by lysine or histidine specific reagent abolished formation of the isoindole derivatives, suggesting that lysine and histidine residues were involved in the OPA-induced inactivation. Taken together, OPA inactivated the alkaline phosphatase from Pinctada fucata by cross-linking lysine and histidine residues at the active site and formed an isoindole group at the substrate binding site of the enzyme.