A highly active alkaline phosphatase from the marine bacterium cobetia

In-Depth Genome Characterization and Pan-Genome Analysis of Strain KMM 296, a Producer of Highly Active Alkaline Phosphatase; Proposal for the Reclassification of Cobetia litoralis and Cobetia pacifica as the Later Heterotypic Synonyms of Cobetia amphilecti and Cobetia marina, and Emended Description of the Species Cobetia amphilecti and Cobetia marina

A strictly aerobic, Gram-stain-negative, rod-shaped, and motile bacterium, designated strain KMM 296, isolated from the coelomic fluid of the mussel Crenomytilus grayanus, was investigated in detail due to its ability to produce a highly active alkaline phosphatase CmAP of the structural family PhoA. A previous taxonomic study allocated the strain to the species Cobetia marina, a member of the family Halomonadaceae of the class Gammaproteobacteria. However, 16S rRNA gene sequencing showed KMM 296's relatedness to Cobetia amphilecti NRIC 0815T. The isolate grew with 0.5-19% NaCl at 4-42 °C and hydrolyzed Tweens 20 and 40 and L-tyrosine. The DNA G+C content was 62.5 mol%. The prevalent fatty acids were C18:1 ω7c, C12:0 3-OH, C18:1 ω7c, C12:0, and C17:0 cyclo. The polar lipid profile was characterized by the presence of phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, and also an unidentified aminolipid, phospholipid, and a few unidentified lipids. The major respiratory quinone was Q-8. According to phylogenomic and chemotaxonomic evidence, and the nearest neighbors, the strain KMM 296 represents a member of the species C. amphilecti. The genome-based analysis of C. amphilecti NRIC 0815T and C. litoralis NRIC 0814T showed their belonging to a single species. In addition, the high similarity between the C. pacifica NRIC 0813T and C. marina LMG 2217T genomes suggests their affiliation to one species. Based on the rules of priority, C. litoralis should be reclassified as a later heterotypic synonym of C. amphilecti, and C. pacifica is a later heterotypic synonym of C. marina. The emended descriptions of the species C. amphilecti and C. marina are also proposed.

Diversity and adaptation properties of actinobacteria associated with Tunisian stone ruins

Stone surface is a unique biological niche that may host a rich microbial diversity. The exploration of the biodiversity of the stone microbiome represents a major challenge and an opportunity to characterize new strains equipped with valuable biological activity. Here, we explored the diversity and adaptation strategies of total bacterial communities associated with Roman stone ruins in Tunisia by considering the effects of geo-climatic regions and stone geochemistry. Environmental 16S rRNA gene amplicon was performed on DNA extracted from stones samples collected in three different sampling sites in Tunisia, along an almost 400km aridity transect, encompassing Mediterranean, semiarid and arid climates. The library was sequenced on an Illumina MiSeq sequencing platform. The cultivable Actinobacteria were isolated from stones samples using the dilution plate technique. A total of 71 strains were isolated and identified based on 16S rRNA gene sequences. Cultivable actinobacteria were further investigated to evaluate the adaptative strategies adopted to survive in/on stones. Amplicon sequencing showed that stone ruins bacterial communities were consistently dominated by Cyanobacteria, followed by Proteobacteria and Actinobacteria along the aridity gradient. However, the relative abundance of the bacterial community components changed according to the geo-climatic origin. Stone geochemistry, particularly the availability of magnesium, chromium, and copper, also influenced the bacterial communities' diversity. Cultivable actinobacteria were further investigated to evaluate the adaptative strategies adopted to survive in/on stones. All the cultivated bacteria belonged to the Actinobacteria class, and the most abundant genera were Streptomyces, Kocuria and Arthrobacter. They were able to tolerate high temperatures (up to 45°C) and salt accumulation, and they produced enzymes involved in nutrients' solubilization, such as phosphatase, amylase, protease, chitinase, and cellulase. Actinobacteria members also had an important role in the co-occurrence interactions among bacteria, favoring the community interactome and stabilization. Our findings provide new insights into actinobacteria's diversity, adaptation, and role within the microbiome associated with stone ruins.

Everything Is Everywhere: Physiological Responses of the Mediterranean Sea and Eastern Pacific Ocean Epiphyte Cobetia Sp. to Varying Nutrient Concentration

Bacteria are essential in the maintenance and sustainment of marine environments (e.g., benthic systems), playing a key role in marine food webs and nutrient cycling. These microorganisms can live associated as epiphytic or endophytic populations with superior organisms with valuable ecological functions, e.g., seagrasses. Here, we isolated, identified, sequenced, and exposed two strains of the same species (i.e., identified as Cobetia sp.) from two different marine environments to different nutrient regimes using batch cultures: (1) Cobetia sp. UIB 001 from the endemic Mediterranean seagrass Posidonia oceanica and (2) Cobetia sp. 4B UA from the endemic Humboldt Current System (HCS) seagrass Heterozostera chilensis. From our physiological studies, both strains behaved as bacteria capable to cope with different nutrient and pH regimes, i.e., N, P, and Fe combined with different pH levels, both in long-term (12 days (d)) and short-term studies (4 d/96 h (h)). We showed that the isolated strains were sensitive to the N source (inorganic and organic) at low and high concentrations and low pH levels. Low availability of phosphorus (P) and Fe had a negative independent effect on growth, especially in the long-term studies. The strain UIB 001 showed a better adaptation to low nutrient concentrations, being a potential N₂-fixer, reaching higher growth rates (μ) than the HCS strain. P-acquisition mechanisms were deeply investigated at the enzymatic (i.e., alkaline phosphatase activity, APA) and structural level (e.g., alkaline phosphatase D, PhoD). Finally, these results were complemented with the study of biochemical markers, i.e., reactive oxygen species (ROS). In short, we present how ecological niches (i.e., MS and HCS) might determine, select, and modify the genomic and phenotypic features of the same bacterial species (i.e., Cobetia spp.) found in different marine environments, pointing to a direct correlation between adaptability and oligotrophy of seawater.

Are the Closely Related Cobetia Strains of Different Species?

Marine bacteria of the genus Cobetia, which are promising sources of unique enzymes and secondary metabolites, were found to be complicatedly identified both by phenotypic indicators due to their ecophysiology diversity and 16S rRNA sequences because of their high homology. Therefore, searching for the additional methods for the species identification of Cobetia isolates is significant. The species-specific coding sequences for the enzymes of each functional category and different structural families were applied as additional molecular markers. The 13 closely related Cobetia isolates, collected in the Pacific Ocean from various habitats, were differentiated by the species-specific PCR patterns. An alkaline phosphatase PhoA seems to be a highly specific marker for C. amphilecti. However, the issue of C. amphilecti and C. litoralis, as well as C. marina and C. pacifica, belonging to the same or different species remains open.

The high catalytic rate of the cold-active Vibrio alkaline phosphatase requires a hydrogen bonding network involving a large interface loop

The role of surface loops in mediating communication through residue networks is still a relatively poorly understood part in the study of cold adaptation of enzymes, especially in terms of their quaternary interactions. Alkaline phosphatase (AP) from the psychrophilic marine bacterium Vibrio splendidus (VAP) is characterized by an analogous large surface loop in each monomer, referred to as the large loop, that hovers over the active site of the other monomer. It presumably has a role in the high catalytic efficiency of VAP which accompanies its extremely low thermal stability. Here, we designed several different variants of VAP with the aim of removing intersubunit interactions at the dimer interface. Breaking the intersubunit contacts from one residue in particular (Arg336) reduced the temperature stability of the catalytically potent conformation and caused a 40% drop in catalytic rate. The high catalytic rates of enzymes from cold‐adapted organisms are often associated with increased dynamic flexibility. Comparison of the relative B‐factors of the R336L crystal structure to that of the wild‐type confirmed surface flexibility was increased in a loop on the opposite monomer, but not in the large loop. The increase in flexibility resulted in a reduced catalytic rate. The large loop increases the area of the interface between the subunits through its contacts and may facilitate an alternating structural cycle demanded by a half‐of‐sites reaction mechanism through stronger ties, as the dimer oscillates between high affinity (active) or low phosphoryl group affinity (inactive).

Isolation and characterization of organophosphorus phosphatases from Bacillus thuringiensis MB497 capable of degrading Chlorpyrifos, Triazophos and Dimethoate

In the current investigation, bacterial strain Bacillus thuringiensis MB497 was examined for production of intracellular and extracellular organophosphorus phosphatase (OPP) enzymes. This strain produced significant amount of extracellular acidic and alkaline phosphatases. Production of neutral phosphatase was negligible. Production of OPP was generally highest at pH 11 and at 45-50 °C. However, activity and stability of OPP was highest at 37 °C and reduced at higher temperatures. OPP production was decreased after 48 h of incubation. Largely, OPP activity was inhibited by SDS and EDTA and significantly enhanced by metals (Zn++, Cu++ and Cd++). Both acidic and alkaline OPPs were capable of bio-precipitation of selected metals (Ni, Mn, Cr and Cd) up to 86-100%. When used against 50 mg/l of three OP pesticides (Chlorpyrifos, Triazophos, and Dimethoate), 81-94.6% degradation of pesticides was observed by alkaline OPP, while acidic OPP showed less degradation (61-70.5%) within 30 min of incubation.

A Novel Alkaline Phosphatase/Phosphodiesterase, CamPhoD, from Marine Bacterium Cobetia amphilecti KMM 296

A novel extracellular alkaline phosphatase/phosphodiesterase from the structural protein family PhoD that encoded by the genome sequence of the marine bacterium Cobetia amphilecti KMM 296 (CamPhoD) has been expressed in Escherichia coli cells. The calculated molecular weight, the number of amino acids, and the isoelectric point (pI) of the mature protein’s subunit are equal to 54832.98 Da, 492, and 5.08, respectively. The salt-tolerant, bimetal-dependent enzyme CamPhoD has a molecular weight of approximately 110 kDa in its native state. CamPhoD is activated by Co²⁺, Mg²⁺, Ca²⁺, or Fe³⁺ at a concentration of 2 mM and exhibits maximum activity in the presence of both Co²⁺ and Fe³⁺ ions in the incubation medium at pH 9.2. The exogenous ions, such as Zn²⁺, Cu²⁺, and Mn²⁺, as well as chelating agents EDTA and EGTA, do not have an appreciable effect on the CamPhoD activity. The temperature optimum for the CamPhoD activity is 45 °C. The enzyme catalyzes the cleavage of phosphate mono- and diester bonds in nucleotides, releasing inorganic phosphorus from p-nitrophenyl phosphate (pNPP) and guanosine 5′-triphosphate (GTP), as determined by the Chen method, with rate approximately 150- and 250-fold higher than those of bis-pNPP and 5′-pNP-TMP, respectively. The Michaelis–Menten constant (K_m), V_max, and efficiency (k_cat/K_m) of CamPhoD were 4.2 mM, 0.203 mM/min, and 7988.6 S⁻¹/mM; and 6.71 mM, 0.023 mM/min, and 1133.0 S⁻¹/mM for pNPP and bis-pNPP as the chromogenic substrates, respectively. Among the 3D structures currently available, in this study we found only the low identical structure of the Bacillus subtilis enzyme as a homologous template for modeling CamPhoD, with a new architecture of the phosphatase active site containing Fe³⁺ and two Ca²⁺ ions. It is evident that the marine bacterial phosphatase/phosphidiesterase CamPhoD is a new structural member of the PhoD family.

Jellyfish Life Stages Shape Associated Microbial Communities, While a Core Microbiome Is Maintained Across All

The key to 650 million years of evolutionary success in jellyfish is adaptability: with alternating benthic and pelagic generations, sexual and asexual reproductive modes, multitudes of body forms and a cosmopolitan distribution, jellyfish are likely to have established a plenitude of microbial associations. Here we explored bacterial assemblages in the scyphozoan jellyfish Chrysaora plocamia (Lesson 1832). Life stages involved in propagation through cyst formation, i.e., the mother polyp, its dormant cysts (podocysts), and polyps recently excysted (excysts) from podocysts – were investigated. Associated bacterial assemblages were assessed using MiSeq Illumina paired-end tag sequencing of the V1V2 region of the 16S rRNA gene. A microbial core-community was identified as present through all investigated life stages, including bacteria with closest relatives known to be key drivers of carbon, nitrogen, phosphorus, and sulfur cycling. Moreover, the fact that half of C. plocamia’s core bacteria were also present in life stages of the jellyfish Aurelia aurita, suggests that this bacterial community might represent an intrinsic characteristic of scyphozoan jellyfish, contributing to their evolutionary success.

Over-expression, characterization, and modification of highly active alkaline phosphatase from a Shewanella genus bacterium

We isolated a Shewanella sp. T3-3 bacterium that yielded highly active alkaline phosphatase (APase). We then cloned the APase gene from Shewanella sp. T3-3 (T3-3AP), and expressed and purified the enzyme from Escherichia coli. Recombinant T3-3AP showed high comparative reactivity on colorimetric (pNPP) and luminescent substrates (PPD and ASP-5). Subsequently, we improved the residual activity after maleimide activation by introducing amino acid substitutions of two Lys residues that were located near the active site. The double mutant enzyme (K161S + K184S) showed much higher residual specific activity after maleimide activation than the wild type enzyme, and had approximately twofold increased sensitivity on sandwich enzyme linked immunosorbent assays (ELISA) compared with calf intestinal APase (CIAP), which is routinely used as a labeling enzyme for ELISA.

Biotechnological Applications of Marine Enzymes From Algae, Bacteria, Fungi, and Sponges

Diversity is the hallmark of all life forms that inhabit the soil, air, water, and land. All these habitats pose their unique inherent challenges so as to breed the "fittest" creatures. Similarly, the biodiversity from the marine ecosystem has evolved unique properties due to challenging environment. These challenges include permafrost regions to hydrothermal vents, oceanic trenches to abyssal plains, fluctuating saline conditions, pH, temperature, light, atmospheric pressure, and the availability of nutrients. Oceans occupy 75% of the earth's surface and harbor most ancient and diverse forms of organisms (algae, bacteria, fungi, sponges, etc.), serving as an excellent source of natural bioactive molecules, novel therapeutic compounds, and enzymes. In this chapter, we introduce enzyme technology, its current state of the art, unique enzyme properties, and the biocatalytic potential of marine algal, bacterial, fungal, and sponge enzymes that have indeed boosted the Marine Biotechnology Industry. Researchers began exploring marine enzymes, and today they are preferred over the chemical catalysts for biotechnological applications and functions, encompassing various sectors, namely, domestic, industrial, commercial, and healthcare. Next, we summarize the plausible pros and cons: the challenges encountered in the process of discovery of the potent compounds and bioactive metabolites such as biocatalysts/enzymes of biomedical, therapeutic, biotechnological, and industrial significance. The field of Marine Enzyme Technology has recently assumed importance, and if it receives further boost, it could successfully substitute other chemical sources of enzymes useful for industrial and commercial purposes and may prove as a beneficial and ecofriendly option. With appropriate directions and encouragement, marine enzyme technology can sustain the rising demand for enzyme production while maintaining the ecological balance, provided any undesired exploitation of the marine ecosystem is avoided.

Extremozymes from Marine Actinobacteria

Marine microorganisms that have the possibility to survive in diverse conditions such as extreme temperature, pH, pressure, and salinity are known as extremophiles. They produce biocatalysts so named as extremozymes that are active and stable at extreme conditions. These enzymes have numerous industrial applications due to its distinct properties. Till now, only a fraction of microorganisms on Earth have been exploited for screening of extremozymes. Novel techniques used for the cultivation and production of extremophiles, as well as cloning and overexpression of their genes in various expression systems, will pave the way to use these enzymes for chemical, food, pharmaceutical, and other industrial applications.

Recombinant production and characterization of a highly active alkaline phosphatase from marine bacterium Cobetia marina

The psychrophilic marine bacterium, Cobetia marina, recovered from the mantle tissue of the marine mussel, Crenomytilus grayanus, which contained a gene encoding alkaline phosphatase (AP) with apparent biotechnology advantages. The enzyme was found to be more efficient than its counterparts and showed k cat value 10- to 100-fold higher than those of all known commercial APs. The enzyme did not require the presence of exogenous divalent cations and dimeric state of its molecule for activity. The recombinant enzyme (CmAP) production and purification were optimized with a final recovery of 2 mg of the homogenous protein from 1 L of the transgenic Escherichia coli Rosetta(DE3)/Pho40 cells culture. CmAP displayed a half-life of 16 min at 45 °C and 27 min at 40 °C in the presence of 2 mM EDTA, thus suggesting its relative thermostability in comparison with the known cold-adapted analogues. A high concentration of EDTA in the incubation mixture did not appreciably inhibit CmAP. The enzyme was stable in a wide range of pH (6.0-11.0). CmAP exhibited its highest activity at the reaction temperature of 40-50 °C and pH 9.5-10.3. The structural features of CmAP could be the reason for the increase in its stability and catalytic turnover. We have modeled the CmAP 3D structure on the base of the high-quality experimental structure of the close homologue Vibrio sp. AP (VAP) and mutated essential residues predicted to break Mg(2+) bonds in CmAP. It seems probable that the intrinsically tight binding of catalytic and structural metal ions together with the flexibility of intermolecular and intramolecular links in CmAP could be attributed to the adapted mutualistic lifestyle in oceanic waters.

A novel bifunctional hybrid with marine bacterium alkaline phosphatase and Far Eastern holothurian mannan-binding lectin activities

A fusion between the genes encoding the marine bacterium Cobetia marina alkaline phosphatase (CmAP) and Far Eastern holothurian Apostichopus japonicus mannan-binding C-type lectin (MBL-AJ) was performed. Expression of the fusion gene in E. coli cells resulted in yield of soluble recombinant chimeric protein CmAP/MBL-AJ with the high alkaline phosphatase activity and specificity of the lectin MBL-AJ. The bifunctional hybrid CmAP/MBL-AJ was produced as a dimer with the molecular mass of 200 kDa. The CmAP/MBL-AJ dimer model showed the two-subunit lectin part that is associated with two molecules of alkaline phosphatase functioning independently from each other. The highly active CmAP label genetically linked to MBL-AJ has advantaged the lectin-binding assay in its sensitivity and time. The double substitution A156N/F159K in the lectin domain of CmAP/MBL-AJ has enhanced its lectin activity by 25 ± 5%. The bifunctional hybrid holothurian's lectin could be promising tool for developing non-invasive methods for biological markers assessment, particularly for improving the MBL-AJ-based method for early detection of a malignant condition in cervical specimens.

Identification and characterization of an extracellular alkaline phosphatase in the marine diatom Phaeodactylum tricornutum

In phosphorus-deficient conditions, Phaeodactylum tricornutum releases an alkaline phosphatase (PtAPase) to the medium that is readily detectable by activity staining. Nucleic acid and amino acid sequence of this alkaline phosphatase (APase) was identified by performing proteomic analysis and database searches. Sequence alignment suggests that PtAPase belongs to the PhoA family, and it possesses key residues at the Escherichia coli PhoA active site. Quantitative PCR results indicate that the induction of APase mRNA transcription is very sensitive to phosphorus availability and population growth. The molecular mass of native PtAPase (148 kDa) determined by gel filtration chromatography indicates that PtAPase, like most PhoA, is homodimeric. Zn and Mg ions are essential cofactors for most PhoA enzymes; however, PtAPase activity did not require Zn ions. In fact, 5 mM Zn²⁺, Mo²⁺, Co²⁺, Cd²⁺, or Cu²⁺ inhibited its enzymatic activity, whereas 5 mM Mn²⁺, Mg²⁺, or Ca²⁺ enhanced its enzymatic activity. The responses of PtAPase to divalent metal ions were different from those of most PhoAs, but were similar to the PhoA in a marine bacterium, Cobetia marina. Phylogenetic analysis shows that homologs of PhoA are also present in other diatom species, and that they clustered in a unique branch away from other PhoA members. PtAPase may represent a novel class of PhoA that helps diatoms to survive in the ocean. Quantification of the PtAPase mRNA may help monitor the physiological condition of diatoms in natural environments and artificial bioreactors.

The biodiscovery potential of marine bacteria: an investigation of phylogeny and function

A collection of marine bacteria isolated from a temperate coastal zone has been screened in a programme of biodiscovery. A total of 34 enzymes with biotechnological potential were screened in 374 isolates of marine bacteria. Only two enzymes were found in all isolates while the majority of enzyme activities were present in a smaller proportion of the isolates. A cluster analysis demonstrated no significant correlation between taxonomy and enzyme function. However, there was evidence of co-occurrence of some enzyme activity in the same isolate. In this study marine Proteobacteria had a higher complement of enzymes with biodiscovery potential than Actinobacteria; this contrasts with the terrestrial environment where the Actinobacteria phylum is a proven source of enzymes with important industrial applications. In addition, a number of novel enzyme functions were more abundant in this marine culture collection than would be expected on the basis of knowledge from terrestrial bacteria. There is a strong case for future investigation of marine bacteria as a source for biodiscovery.

Cloning and expression of a highly active recombinant alkaline phosphatase from psychrotrophic Cobetia marina

Alkaline phosphatase catalyzes the hydrolysis of phosphomonoesters and is widely used in molecular biology techniques and clinical diagnostics. We expressed a recombinant alkaline phosphatase of the marine bacterium, Cobetia marina, in Escherichia coli BL21 (DE3). The recombinant protein was purified with a specific activity of 12,700 U/mg protein, which is the highest activity reported of any bacterial alkaline phosphatase studied to date. The molecular mass of the recombinant protein was 55-60 kDa, as determined by SDS-PAGE, and was observed to be a dimer by gel filtration analysis. The enzyme was optimally active at 45°C and the recombinant alkaline phosphatase efficiently hydrolyzed a phosphoric acid ester in luminescent and fluorescent substrates. Therefore, this enzyme can be considered to be extremely useful as a label conjugated to an antibody.

Cloning and expression pattern of alkaline phosphatase during the development of Paralichthys olivaceus

Alkaline phosphatases are ubiquitous enzymes involved in many important biological processes. Mammalian tissue-nonspecific alkaline phosphatase has long been thought to feature in embryonic development and bone formation. In this study, an alkaline phosphatase (ALP) gene from Paralichthys olivaceus was identified by rapid amplification of cDNA ends and genome-walking PCR. The ALP gene extends 10,141 bp and contains 11 exons and 10 introns. The open reading frame of the ALP transcript consists of 1,431 bp, which encodes 476 amino acids products named as POALP. An analysis of its secondary and tertiary structure revealed that the POALP was conserved in different species, but one disulfide linkage made it possible to adapt to low-temperature environment. The ALP activity was found to be first detectable in the embryo before hatching. The POALP was distributed ubiquitously in the body of P. olivaceus and was particularly high in the digestive tract. These findings suggest the potential role of POALP in nutrient absorption and transportation. During the pre-metamorphosis (F stage), ALP gene expression is 2.5-folds of that in the pro-metamorphosis (E stage); but in the post-metamorphosis (I stage), it was 1.8-folds of that of pro-metamorphosis. Exogenetic thyroxine (T4) and thiourea (TU) influenced the ALP gene expression significantly during the metamorphosis. Bioinformatics analysis showed that Japanese flounder ALP promoter region contained promoter sequence and putative recognition site for several transcriptional factors, including SREBP-1, SYR, and CdxA. In vitro promoter assays employing EGFP reporter system demonstrated that the promoter of ALP was active.

Responses of the marine bacterium Pseudomonas fluorescens to an excess of heavy metals: physiological and biochemical aspects

A Pseudomonas fluorescens strain was isolated from oxic marine sediments obtained from the strand zone of the St Anne Bay (a moderately metal-contaminated site to the west of Cherbourg harbour). The strain, which exhibited a high tolerance to metal contamination when cultivated (minimal inhibitory concentration=950 microM [62 mg L(-1)] for Zn, 660 microM [42 mg L(-1)] for Cu, and 505 microM [57 mg L(-1)] for Cd), was further characterized by its physiological and biochemical responses to metal additions to the culture medium. Bacterial growth was significantly disturbed by 380 microM Zn (25 mg L(-1)), 315 microM Cu (20 mg L(-1)) and 90 microM Cd (10 mg L(-1)). The Zn-containing alkaline phosphatase was studied as an intoxication biomarker. Its activity was stimulated (+9%) by an excess of Zn, but inhibited by Cd (-55%) and Cu (-10%), these two elements could displace the native Zn or/and disturb the enzyme 3D-structure. Bacterial O(2) consumption was recorded as a global physiological response to metal stress. This parameter dropped with increasing Cd and Cu contamination (-49% and -45%, respectively, at 20 mg L(-1)). By contrast, Zn increased O2 consumption (approximately +40% for the different tested concentrations). The proteomes of bacteria grown in the presence or absence of 20 mg metal L(-1) were characterized by 2D-gel electrophoresis. The number of spots exhibiting a difference in intensity between the contaminated sample and the control was 65, 68, and 103, for Zn, Cu and Cd, respectively. Among them, 45, 61 and 82 spots respectively appeared de novo or increased in intensity, indicative of metal-stimulated synthesis, particularly for Cu and Cd. In summary, whereas Cd and Cu treatments both stressed cells and slowed down primary metabolism to differing extents, Zn has a stimulating action on several physiological and biochemical parameters.

A novel glycosylphosphatidylinositol-anchored alkaline phosphatase dwells in the hepatic duct of the pearl oyster, Pinctada fucata

Alkaline phosphatases are ubiquitous enzymes involved in many important biological processes. Mammalian tissue-nonspecific alkaline phosphatase (TNAP) has long been thought to play an important role in bone mineralization. In this study, we identified a full-length cDNA encoding a potential alkaline phosphatse from pearl oyster Pinctada fucata by RT-PCR and RACE and designated the encoded protein as PFAP. The sequence of PFAP shares an overall similarity of 67% with that of human TNAP. Prediction and analysis of its secondary and tertiary structure revealed that the PFAP contains two mammalian-specific regions, the crown domain, involved in collagen binding, and the calcium binding domain, which hint its potential ability to participate in biomineralization. RT-PCR and in situ hybridization showed that the PFAP mRNA distributes specifically in the hepatic duct of the digestive diverticula. These findings implied its possible role in calcium absorption and transportation. In vivo, PFAP could be specifically released by phosphatidylinositol-specific phospholipase C (PIPLC), suggesting it is glycophosphatidylinositol-anchored to the plasma membrane. Therefore, a human growth hormone-PFAP fusion was constructed to locate the cleavage/attachment site. Immunofluorescent labeling and immunoblotting showed that Asn-477 is the cleavage/attachment site and the 25-residue peptide COOH-terminal to Asn-477 is removed during glycophosphatidylinositol anchoring. This research will hopefully pave the way to illustrate the role PFAP plays in calcium transportation related to pearl biomineralization.