Characterization and overexpression of a novel ß-agarase from Thalassomonas agarivorans.

AIMS: The agarase from Thalassomonas agarivorans BCRC 17492 was cloned and overexpressed in Escherichia coli. The characterization of the novel agarase was performed. METHODS AND RESULTS: The genomic library of T. agarivorans BCRC 17492 was constructed for screening agarase gene. The novel ß-agarase, namely AgaB1, was successfully identified and shared only 57% identity to reported agarase from Alteromonas sp. To characterize the AgaB1 protein, the recombinant AgaB1 can be obtained by heterologous expression in E. coli. The agarase activity of AgaB1 was achieved at 30·25 U per mg at 35°C. According to the analysis of optimal conditions, the highest activity of AgaB1 was attained at 40°C, pH 7·4 and 200 mmol l(-1) NaCl, and half-life of AgaB1 can be maintained for almost 1 h at 40°C. Further determination of substrate hydrolysis indicated that AgaB1 had possession of both endo- and exolytic activity, and neoagarobiose was the major hydrolysis product by TLC and high-performance liquid chromatograph/mass spectrometer (HPLC/MS) analysis. CONCLUSIONS: We have successfully cloned and overexpressed the novel ß-agarase from T. agarivorans BCRC 17492 in E. coli. The high yield and detailed characterization of recombinant AgaB1 was provided. SIGNIFICANT AND IMPACT OF THE STUDY: AgaB1 was the first ß-agarase that was cloned and described from Thalassomonas species. In the light of properties of AgaB1, it has the potential as the biocatalyst for industrial applications.

Development of a sensitive and specific LAMP PCR assay for detection of fish pathogen Lactococcus garvieae.

Based on use of a loop-mediated isothermal amplification (LAMP) identification protocol, this study attempted to detect Lactococcus garvieae in fish by using primer sets designed from an L. garvieae alpha/beta fold family hydrolase gene. Reaction time and temperatures were optimized for 60 min at 60°C with the resulting amplicons visualized by adding SYBR Green I to the reaction tube. The assay specificity was assessed using 45 different bacterial strains. Positive results were observed in all 30 L. garvieae isolates from various aquatic animals. No false-positive results were observed in 15 non-L. garvieae strains. The detection limit of the LAMP assay was 10-fold more sensitive than the conventional polymerase chain reaction (PCR) targeting 16S rDNA when using purified L. garvieae DNA. The detection limit of the LAMP assay was approximately 300 colony-forming units (CFU) using crude bacterial lysates, 100-fold more sensitive than PCR. Furthermore, L. garvieae in spleen, kidney and brain of experimentally challenged tilapia and grey mullet were detected using this optimized LAMP assay. Results of this study demonstrate the effectiveness of LAMP in providing a rapid yet simple test for detecting L. garvieae in fish.

Development of a multiplex polymerase chain reaction to detect five common Gram-negative bacteria of aquatic animals.

A multiplex polymerase chain reaction (m-PCR) technique was developed as a rapid and accurate diagnostic tool for identifying five major Gram-negative bacilli -Vibrio vulnificus, V. parahaemolyticus, Aeromonas hydrophila, Chryseobacterium meningosepticum and Edwardsiella tarda- that cause major diseases in cultured aquatic animals in Taiwan. The expected amplicons for V. vulnificus, V. parahaemolyticus, A. hydrophila, C. meningosepticum and E. tarda were 410, 368, 685, 180 and 230bp, respectively. The assay was shown to be specific for the target pathogens. The sensitivities of detection were estimated to be 20.5fg∼200pg of genomic DNA or 10(2) ∼10(4) colony-forming units (cfu) of bacterial isolates when adopted as PCR templates. The m-PCR was capable of simultaneously amplifying target fragments from bacterial genome DNA mixed with the DNA extracted from viscera and tissues taken from fish without affecting the performance of the method.

Re-epithelialization in cornea organ culture after chemical burns and excimer laser treatment.

OBJECTIVE: To describe the epithelial healing rates observed in freshly cultured rabbit corneas chemically burned with high-concentration hydrochloric acid (HCl) and sodium hydroxide (NaOH) and subsequently treated with phototherapeutic keratectomy (PTK). METHODS: We obtained 126 fresh corneoscleral rims from cadaveric New Zealand white rabbits. Each cornea was exposed to 4-mm cellulose sponges soaked in a solution of topical 0.9% isotonic sodium chloride solution, 2M HCl, or 0.5M NaOH. A transepithelial PTK (6-mm zone; 100-microm ablation depth) was then performed using the excimer laser (150-mJ/cm(2) energy pulse; 20 nanosecond duration; and 10-Hz frequency). Corneas were placed in tissue culture, and 1 cornea from each group was taken out of culture each day after treatment. Re-epithelialization was monitored by means of fluorescein staining, slitlamp photography, and histopathological analysis. RESULTS: Corneas treated with HCl and NaOH exhibited immediate epithelial defects that slowly healed over time. In PTK-treated corneas, the re-epithelialization rate was accelerated compared with that of controls (P =.003 for the HCl group, and P<.001 for the NaOH group). The new epithelial layers were smoother in PTK-treated corneas, as confirmed by results of histopathological analysis. CONCLUSION: Corneal damage caused by HCl and NaOH may be modulated in vitro by PTK in this rabbit model. CLINICAL RELEVANCE: After corneal chemical damage, 193-nm excimer laser PTK accelerates epithelial wound healing.

Lactococcus garvieae infection in the giant freshwater prawn Macrobranchium rosenbergii confirmed by polymerase chain reaction and 16S rDNA sequencing.

An epizootic bacterial infection in the giant freshwater prawn Macrobranchium rosenbergii occurred in Taiwan from May to June 1999. The cumulative mortality was approximately 30 to 75%. The diseased prawns showed opaque and whitish muscles and were approximately 2 mo old with total lengths from 5 to 6 cm. Histopathologically, they showed marked edema and necrotic lesions with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Three isolates from diseased prawns at different farms were tested using the API 20 Strepsystem and conventional tests and identified as Lactococcus garvieae. Experimental infections with these isolates gave gross signs and histopathological changes similar to those seen in the naturally infected prawns. The LD50 value of isolate MR1 was 6.6 x 10(5) colony forming units/prawn. Identification of MR1 was confirmed by a PCR assay for L. garvieae that gave the expected amplicon of 1100 bp. In addition, its 16S rDNA sequence (GenBank accession number AF283499) gave 99% sequence identity to Enterococcus seriolicida (synonym L. garvieae; GenBank accession number AF061005). This is the first report of confirmed L. garvieae infection in prawn aquaculture.

Histidine residues 102 and 117 of MelC1 play different roles in the chaperone function for Streptomyces apotyrosinase.

MelC1 regulates the copper incorporation and secretion of Streptomyces apotyrosinase (MelC2) via a transient, competent complex formation. His-102 and His-117 of the chaperone-like MelC1 are known to play important roles in this trans-activation activity of MelC1. In this study, we studied the side chain requirement at these two residues for MelC1 function. Substitution of His-117 with polar, charged, or hydrophobic amino acid resulted in complete abolishment of the tyrosinase activity but no effect on its secretion. When similar amino acid substitutions were introduced at His-102, both the secretion and the enzymatic activity of tyrosinase were blocked to different extents. Furthermore, the tyrosinase activity of the His-117 mutants but not the His-102 mutants could be partially reactivated by in vitro copper reconstitution. Notably, the defects in the MelC1 mutant protein did not impair the formation of the MelC1-MelC2 binary complex, but rather produced an incompetent complex. In summary, our results reveal that His-102 and His-117 of MelC1 play different roles in MelC1 functions. In particular, His-117 of MelC1 plays a pivotal role in regulation of the copper incorporation but not the secretion of apotyrosinase, while His-102 plays a dual role in both the secretion and the activation of apotyrosinase.

Secretion of the Streptomyces tyrosinase is mediated through its trans-activator protein, MelC1.

The tyrosinase of Streptomyces antibioticus is encoded by the second open reading frame, melC2 of the melanin operon (melC). The upstream open reading frame melC1 specifies a 146-amino acid protein with a typical NH2-terminal signal-peptide characteristic of a secretory protein. The MelC1 protein is involved in the transfer of copper ion to apotyrosinase MelC2 via binary complex formation (Lee, Y.-H. W., Chen, B.-F., Wu, S.-Y., Leu, W.-M., Lin, J.-J., Chen, C. W., and Lo, S. J. (1988) Gene (Amst.) 65, 71-81; Chen, L.-Y., Leu, W.-M., Wang, K.-T., and Lee, Y.-H.W. (1992) J. Biol. Chem. 267, 20100-20107). To investigate whether the export of tyrosinase is also dependent on MelC1, a mutational study of its signal-peptide sequence was performed. Four different mutants were obtained. Mutation at the positively charged region (mutant M-6LE, Arg6-Arg7----Leu6-Glu7) or the hydrophobic region (mutant M-16D, Val16----Asp16) led to Mel- phenotypes. These lesions caused a severe 7-10-fold reduction of the export of both the MelC1 and MelC2 proteins and a concomitant accumulation of the two proteins in the cytosolic fraction. The cell-associated tyrosinase activity in M-6LE but not in the M-16D mutant was dramatically reduced to 4% of the activity found in the wild type strain, suggesting that the basic NH2 terminus of MelC1 is also important for the trans-activation function of this protein. Nevertheless, the defects on the trans-activation and/or secretory functions of MelC1 in mutants M-6LE and M-16D are not due to the impairment of the formation of the MelC1.MelC2 complex. The translation of melanin operon genes in these two mutants also decreased. In contrast, the tyrosinase activity and the secretion of MelC2 were not affected if the mutations occurred at the putative cleavage site of the signal peptidase (e.g. mutant M-29SM, Arg29-Ala30----Ser29-Met30 or mutant 29-SMG, Arg29-Ala30-Asp31----Ser29-Med30-Gly31+ ++). Additionally, tyrosinase activity and its export were abolished in a MelC1-negative mutant, M-950. Taken together, these results demonstrate that a functional MelC1 is essential for tyrosinase secretion and activity. Furthermore, the results suggest that like other secretory proteins, basic and hydrophobic residues in the MelC1 signal sequence are an important feature of the signal-peptide and play a pivotal role in the secretion of both the MelC1 and MelC2 proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Chicken mitochondrial cytochrome C oxidase subunit II: comparative analysis among the vertebrates.

The chicken cytochrome c oxidase subunit II (COII) was cloned and sequenced. A comparison of the deduced chicken COII sequence with 4 other vertebrate counterparts revealed 64-66% amino acid sequence homology and 68-70% nucleotide sequence homology. Four peptide segments each of nine amino acids long are highly conserved across the 5 species. A redox-center was formed by three of these highly conserved domains, which include two invariant Cys and two invariant His residues for copper ion coordination, three strictly conserved Glu or Asp residues for cytochrome c binding, and highly conserved aromatic acid residues for electron transfer.

Molecular cloning and characterization of a neurotoxic phospholipase A2 from the venom of Taiwan habu (Trimeresurus mucrosquamatus).

Using gel-filtration chromatography and reverse-phase (RP) HPLC we have purified a presynaptic neurotoxin (designated as trimucrotoxin) from the crude venom of Taiwan habu (Trimeresurus mucrosquamatus). Its complete primary structure was solved by an automated N-terminal sequencing and cDNA sequencing method. The enzyme inhibited the twitch of the chick biventer cervicis muscle at 0.1-1 micrograms/ml and showed lethality in mice (LD50 = 1.2 micrograms/g, when given intravenously). Trimucrotoxin exists mainly as a homodimer of 14 kDa subunits as shown by a gel-filtration experiment, and dissociates into monomers during SDS/PAGE in the absence of Ca2+. However, most of trimucrotoxin migrated as slowly as a trimer during nondenaturing SDS/PAGE in the presence of Ca2+ or Sr2+. Its amino acid sequence identity to crotoxin B and agkistrodotoxin is about 75%, and its cDNA sequence is 82% identical to that of crotoxin B. Rabbit antiserum against trimucrotoxin also cross-reacted with the other crotalid neurotoxic phospholipases A2. Furthermore, the purified acidic subunit of crotoxin potentiated the neurotoxicity of trimucrotoxin. A comparison of the sequences of these crotalid neurotoxins revealed some common features of the possible neurotoxic sites, including residues 6, 11, 76-81 and 119-125.