Salt Mediated Modulation of Autolysis of Thermolysin-Like Proteinase, Salilysin, Isolated from a Moderate Halophile, Chromohalobacter salexigens DSM3043

Halophilic salilysin is first synthesized as a pro-form, which has been shown autolysis activity to process pro-region (55 amino acids long) three times to form intermediate 1 (I1), intermediate 2 (I2) and final mature (M) salilysin. The autolysis of I1- to M-form salilysin in vitro was significantly accelerated with increasing NaCl concentration up to 4 M. Strong salting-out salts, (NH₄)₂SO₄, Na₂SO₄ and MgSO₄, were more effective, suggesting that autolysis is enhanced by inter-molecular association or structure compaction or both. However, MgCl_2, a salting-in salt, was also effective, suggesting that other mechanisms, such as charge shielding and ionic binding to this halophilic protein, operated. Autolytic cleavage at site 3 resulted in mixed formation of correctly and incorrectly processed mature forms in the absence of salt, indicating that salt affected the accuracy of autolytic cleavage reaction. Far UV circular dichroism (CD) measurements indicated that E167A pro-salilysin showed an identical CD spectrum to the wild-type mature salilysin, suggesting pro-form has a proper fold for proteolytic activity. Thermal scanning indicated that E167A pro-salilysin was more heat-stable by ~ 10 °C than mature form. The CD spectra, thermal stability and modeling structure of salilysin clearly suggested that pro-salilysin is folded to the same structure as native form and is functional for autolysis.

Salt-enhanced processing, proteolytic activity and stability of halophilic thermolysin-like proteinase, salilysin, isolated from a moderate halophile, Chromohalobacter salexigens DSM3043

Moderately halophilic bacterium, Chromohalobacter salexigens DSM3043, has a gene Csal_2537 encoding thermolysin-like M4 proteinase. This gene was cloned to pET expression vectors, resulting in high expression of recombinant proteinase, named as salilysin (salinity-dependent thermolysin-like proteinase), in Escherichia coli cytoplasm. This gene encodes precursor form of salilysin containing 348 amino acid residues (Pro-salilysin) consisting of 55 amino acids pro-sequence and following mature proteinase. Pro-sequence was cleaved three times to form intermediate 1, intermediate 2 and final mature salilysin. The processing rate was greatly accelerated in a salt concentration-dependent manner. Purified inactive mutant Pro-E167A-salilysin was correctly processed by purified mature salilysin, indicating that autolysis and inter-molecular processing occurred in its maturation processes. Proteolytic activity of mature salilysin against both peptide and protein substrates was also enhanced along with the addition of higher concentration of salt, 0-3.2 M NaCl, consistent with its halophilic origin. Mature salilysin was stabilized by ~8 °C in the presence of 1 M NaCl by thermal scanning using circular dichroism. One of the precursor form, intermediate 1, showed ~20 °C higher denaturation temperature than mature form, suggesting rigid and stable structure of this precursor form.

Catalytic mechanism and evolutionary characteristics of thioredoxin from Halobacterium salinarum NRC-1

Thioredoxin (TRX) is an important antioxidant against oxidative stress. TRX from the extremely halophilic archaeon Halobacterium salinarum NRC-1 (HsTRX-A), which has the highest acidic residue content [(Asp + Glu)/(Arg + Lys + His) = 9.0] among known TRXs, was chosen to elucidate the catalytic mechanism and evolutionary characteristics associated with haloadaptation. X-ray crystallographic analysis revealed that the main-chain structure of HsTRX-A is similar to those of homologous TRXs; for example, the root-mean-square deviations on C^α atoms were <2.3 Å for extant archaeal TRXs and <1.5 Å for resurrected Precambrian TRXs. A unique water network was located near the active-site residues (Cys45 and Cys48) in HsTRX-A, which may enhance the proton transfer required for the reduction of substrates under a high-salt environment. The high density of negative charges on the molecular surface (3.6 × 10^-3 e Å^-2) should improve the solubility and haloadaptivity. Moreover, circular-dichroism measurements and enzymatic assays using a mutant HsTRX-A with deletion of the long flexible N-terminal region (Ala2-Pro17) revealed that Ala2-Pro17 improves the structural stability and the enzymatic activity of HsTRX-A under high-salt environments (>2 M NaCl). The elongation of the N-terminal region in HsTRX-A accompanies the increased hydrophilicity and acidic residue content but does not affect the structure of the active site. These observations offer insights into molecular evolution for haloadaptation and potential applications in halophilic protein-related biotechnology.

A comparison of the effect of large and small metal-on-metal bearings in total hip arthroplasty on metal ion levels and the incidence of pseudotumour

Aims

The purpose of this study was to compare two different types of metal-on-metal (MoM) bearing for total hip arthroplasty (THA): one with a large femoral head (38 mm to 52 mm) and the other with a conventional femoral head (28 mm or 32 mm). We compared clinical outcome, blood metal ion levels, and the incidence of pseudotumour in the two groups.

Patients and Methods

Between December 2009 and December 2011, 62 patients underwent MoM THA with a large femoral head (Magnum group) and 57 patients an MoM THA with a conventional femoral head (conventional group). Clinical outcome was assessed using the Harris Hip score, University of California, Los Angeles (UCLA) activity score and EuroQol-5D (EQ-5D). Blood metal ion levels were measured and MRI scans were analyzed at a minimum of five years postoperatively.

Results

No acetabular component was implanted with more than 50° of inclination in either group. The Harris Hip Score, UCLA activity score, and EQ-5D improved postoperatively in both groups; no significant clinical differences were noted between the groups. The blood cobalt ion levels in the conventional group continued to rise postoperatively to five years while reaching a plateau at two years postoperatively in the Magnum group. At five years, the mean cobalt ion level of 1.16 μg/l (sd 1.32) in the Magnum group was significantly lower than the 3.77 μg/l (sd 9.80) seen in the conventional group (p = 0.0015). The incidence of moderate to severe pseudotumour was 4.7% in the Magnum group and 20.6% in the conventional group. There were no dislocations in the Magnum group and two in the conventional group. One patient in the Magnum group underwent revision for pseudotumour at 4.7 years postoperatively.

Conclusion

At five years, a well-positioned large head MoM THA has a significantly lower level of metal ion release and a lower incidence of moderate to severe pseudotumour than a MoM bearing of conventional size. Cite this article: Bone Joint J 2018;100-B:1018–24.

Structure of a highly acidic β-lactamase from the moderate halophile Chromohalobacter sp. 560 and the discovery of a Cs(+)-selective binding site

Environmentally friendly absorbents are needed for Sr(2+) and Cs(+), as the removal of the radioactive Sr(2+) and Cs(+) that has leaked from the Fukushima Nuclear Power Plant is one of the most important problems in Japan. Halophilic proteins are known to have many acidic residues on their surface that can provide specific binding sites for metal ions such as Cs(+) or Sr(2+). The crystal structure of a halophilic β-lactamase from Chromohalobacter sp. 560 (HaBLA) was determined to resolutions of between 1.8 and 2.9 Å in space group P31 using X-ray crystallography. Moreover, the locations of bound Sr(2+) and Cs(+) ions were identified by anomalous X-ray diffraction. The location of one Cs(+)-specific binding site was identified in HaBLA even in the presence of a ninefold molar excess of Na(+) (90 mM Na(+)/10 mM Cs(+)). From an activity assay using isothermal titration calorimetry, the bound Sr(2+) and Cs(+) ions do not significantly affect the enzymatic function of HaBLA. The observation of a selective and high-affinity Cs(+)-binding site provides important information that is useful for the design of artificial Cs(+)-binding sites that may be useful in the bioremediation of radioactive isotopes.

Structural characteristics of alkaline phosphatase from the moderately halophilic bacterium Halomonas sp. 593

Alkaline phosphatase (AP) from the moderate halophilic bacterium Halomonas sp. 593 (HaAP) catalyzes the hydrolysis of phosphomonoesters over a wide salt-concentration range (1-4 M NaCl). In order to clarify the structural basis of its halophilic characteristics and its wide-range adaptation to salt concentration, the tertiary structure of HaAP was determined by X-ray crystallography to 2.1 Å resolution. The unit cell of HaAP contained one dimer unit corresponding to the biological unit. The monomer structure of HaAP contains a domain comprised of an 11-stranded β-sheet core with 19 surrounding α-helices similar to those of APs from other species, and a unique `crown' domain containing an extended `arm' structure that participates in formation of a hydrophobic cluster at the entrance to the substrate-binding site. The HaAP structure also displays a unique distribution of negatively charged residues and hydrophobic residues in comparison to other known AP structures. AP from Vibrio sp. G15-21 (VAP; a slight halophile) has the highest similarity in sequence (70.0% identity) and structure (C(α) r.m.s.d. of 0.82 Å for the monomer) to HaAP. The surface of the HaAP dimer is substantially more acidic than that of the VAP dimer (144 exposed Asp/Glu residues versus 114, respectively), and thus may enable the solubility of HaAP under high-salt conditions. Conversely, the monomer unit of HaAP formed a substantially larger hydrophobic interior comprising 329 C atoms from completely buried residues, whereas that of VAP comprised 264 C atoms, which may maintain the stability of HaAP under low-salt conditions. These characteristics of HaAP may be responsible for its unique functional adaptation permitting activity over a wide range of salt concentrations.

Surface acidic amino acid of Pseudomonas/Halomonas chimeric nucleoside diphosphate kinase leads effective recovery from heat-denaturation

One of the hallmarks of halophilic properties is reversibility of thermal unfolding. A nucleoside diphosphate kinase (NDK) from a moderate halophile Halomonas sp. 593 (HaNDK) follows this behavior. His-tagged chimeric NDK (HisPaHaNDK) consisting of an N-terminal half of a non-halophilic Pseuodomonas aeruginosa NDK (PaNDK) and a Cterminal half of HaNDK loses this reversible property, indicating a critical role of the N-terminal portion of PaNDK in determining the reversibility of the chimeric protein. Various mutations were introduced at Arg45 and Lys61, based on the model NDK structure. It appears that having Glu at position 45 is critical in conferring the thermal reversibility to HisPa- HaNDK chimeric protein.

Effects of salt and ligand concentrations on the thermal unfolding and refolding of halophilic starch-binding domain from Kocuria varians α-amylase

The starch binding domain of α-amlylase from moderate halophile was expressed in E. coli with His tag (His- SBD12) and characterized for its halophilic properties. His-SBD12 was stable up to 35°C and showed binding activity, although at reduced level, to amylose even in the absence of NaCl. Both NaCl and specific ligands exhibited insignificant influence on the secondary structure of His-SBD12, but showed significant stabilization effects against thermal unfolding concentration-dependently, showing its halophilic properties. NaCl increased thermal stability of His-SBD12 by 4°C at 0.2 M and 15°C at 2 M, and enhanced refolding rate by ~7-fold at 0.2 M and ~170-fold at 2 M. Its specific ligands, β- cyclodextrin (at 3 mM) and maltose (at 470 mM), also stabilized the protein by 11° C, most likely reflecting affinity difference between these two ligands. However, they showed marginal effects on refolding rate. These observations suggest that although binding of NaCl and specific ligands to the native structure can explain their stabilization effects on His- SBD12, it is not a sole factor for modulating their effects on folding of His-SBD12.

A structural mechanism for dimeric to tetrameric oligomer conversion in Halomonas sp. nucleoside diphosphate kinase

Nucleoside diphosphate kinase (NDK) is known to form homotetramers or homohexamers. To clarify the oligomer state of NDK from moderately halophilic Halomonas sp. 593 (HaNDK), the oligomeric state of HaNDK was characterized by light scattering followed by X-ray crystallography. The molecular weight of HaNDK is 33,660, and the X-ray crystal structure determination to 2.3 and 2.7 Å resolution showed a dimer form which was confirmed in the different space groups of R3 and C2 with an independent packing arrangement. This is the first structural evidence that HaNDK forms a dimeric assembly. Moreover, the inferred molecular mass of a mutant HaNDK (E134A) indicated 62.1-65.3 kDa, and the oligomerization state was investigated by X-ray crystallography to 2.3 and 2.5 Å resolution with space groups of P2(1) and C2. The assembly form of the E134A mutant HaNDK was identified as a Type I tetramer as found in Myxococcus NDK. The structural comparison between the wild-type and E134A mutant HaNDKs suggests that the change from dimer to tetramer is due to the removal of negative charge repulsion caused by the E134 in the wild-type HaNDK. The higher ordered association of proteins usually contributes to an increase in thermal stability and substrate affinity. The change in the assembly form by a minimum mutation may be an effective way for NDK to acquire molecular characteristics suited to various circumstances.

The solubility of nucleobases in aqueous arginine solutions

Arginine is widely used in refolding, purification, analysis and formulation of proteins, primarily because of its ability to suppress protein-protein and protein-surface interactions. Such a property of arginine is at least partially attributable to its affinity for the aromatic groups present in proteins. Herein, we have extended its study further to characterize arginine in terms of its affinity for heteroaromatic compounds, using nucleobases as a model compound. Arginine increased the solubility of all nucleobases tested when these nucleobases were electrically neutral, indicating that arginine interacts favorably with these heteroaromatics. The observed effects of arginine on the solubility of nucleobases suggest that arginine should stabilize the melted state of nucleic acids, in which the nucleobases are more solvent-exposed. In an acidic solution, to our surprise, arginine decreased the solubility of positively charged nucleobases.

Engineering of halophilic enzymes: two acidic amino acid residues at the carboxy-terminal region confer halophilic characteristics to Halomonas and Pseudomonas nucleoside diphosphate kinases

Nucleoside diphosphate kinase from Halomonas sp. 593 (HaNDK) exhibits halophilic characteristics. Residues 134 and 135 in the carboxy-terminal region of HaNDK are Glu-Glu, while those of its homologous counterpart of non-halophilic Pseudomonas NDK (PaNDK) are Ala-Ala. The double mutation, E134A-E135A, in HaNDK results in the loss of the halophilic characteristics, and, conversely, the double mutation of A134E-A135E in PaNDK confers halophilic characters to this enzyme, indicating that the charged state of these two residues that are located in the C-terminal region plays a critical role in determining halophilic characteristics. The importance of these two residues versus the net negative charges will be discussed in relation to the halophilicity of NDK.

Chromohalobacter japonicus sp. nov., a moderately halophilic bacterium isolated from a Japanese salty food

A Gram-negative, non-spore-forming, rod-shaped, motile bacterium, designated strain 43T, was isolated from a Japanese salty food and then subjected to a polyphasic taxonomic study. Strain 43T is moderately halophilic, growing at NaCl concentrations in the range 5–25 % (w/v), with optimum growth between 7.5 and 12.5 % (w/v) NaCl. Growth occurs at temperatures from 15 to 42 °C (optimally at 28–37 °C) and at pH 5.5–9.0 (optimally at pH 7.0–8.0). A phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain 43T belongs to the genus Chromohalobacter. The closest relatives were Chromohalobacter canadensis ATCC 43984T (99.3 % 16S rRNA gene sequence similarity), Chromohalobacter beijerinckii ATCC 19372T (99.1 %), Chromohalobacter sarecensis LV4T (98.3 %), Chromohalobacter nigrandesensis LTS-4NT (97.9 %) and Chromohalobacter marismortui ATCC 17056T (97.9 %). The DNA G+C content was 62.9 mol%, which is within the range described for the genus Chromohalobacter. DNA–DNA hybridization studies between strain 43T and C. canadensis CECT 5385T and C. beijerinckii DSM 7218T showed 38 and 49 % relatedness, respectively; lower DNA–DNA hybridization percentages were obtained with respect to other related Chromohalobacter species. The major fatty acids of strain 43T were C16 : 0, C19 : 0 cyclo ω8c and C12 : 0 3-OH. Overall, the phenotypic, genotypic and phylogenetic results demonstrated that strain 43T represents a novel species within the genus Chromohalobacter. The name Chromohalobacter japonicus sp. nov. is proposed, with strain 43T (=CECT 7219T =CCM 7416T) as the type strain.

Dimeric structure of nucleoside diphosphate kinase from moderately halophilic bacterium: contrast to the tetramericPseudomonascounterpart

Light scattering and chemical cross-linking analyses of nucleoside diphosphate kinase (NDK) from moderate halophile, Halomonas sp. 593 (HaNDK), unambiguously demonstrated that this enzyme formed a dimeric structure, in contrast to the Pseudomonas NDK (PaNDK), a nonhalophilic counterpart, and other NDKs from Gram-negative bacteria, which all formed a tetrameric structure. Comparison of HaNDK and PaNDK showed that the HaNDK was less thermally stable than the PaNDK: the optimum temperature of PaNDK enzyme activity was 20 degrees C higher than that of HaNDK. However, the HaNDK readily refolded and reassembled back to the active dimeric structure, upon heat denaturation at 0.2 M NaCl, as soon as the temperature was lowered. On the contrary, the thermally more stable PaNDK was irreversibly denatured at its melting temperature.

Efficient expression of haloarchaeal nucleoside diphosphate kinase via strong porin promoter in moderately halophilic bacteria

Enzymes from extremely halophilic archaea require high concentration of salts for their proper folding and consequently are expressed as an unfolded and inactive form in Escherichia coli. Moderate halophile, which accumulates protein stabilizers, i.e., compatible solutes, is an attractive host cell for the recombinant production of heterologous proteins, since such protein stabilizers may help folding of expressed proteins. Here, we succeeded in efficient expression and purification to homogeneity of recombinant haloarchaeal nucleoside diphosphate kinase (HsNDK) in moderate halophile using newly isolated strong porin promoter.

Contribution of halophilic nucleoside diphosphate kinase sequence to the heat stability of chimeric molecule

A halophilic nucleoside diphosphate kinase from a moderate halophile, Halomonas sp. 593 (593NDK), was found to be resistant to heat treatment, as indicated by the high level of activity recovery after heating at high temperatures. This is due to reversibility of thermal unfolding, not the high melting temperature, of the protein. The highly homologous NDK from non-halophilic organism, Pseudomonas aeruginosa, showed instability against heat treatment. Chimeric molecules consisting of each half of these two NDKs were constructed and characterized for their heat stability. The results showed that the N-terminal half of 593NDK contributes to the heat stability of the proteins. We discuss the possible reason for the observed difference in resistance to heat treatment between the 593NDK and PaNDK and between two chimeric proteins.

Intake of arsenic from water, food composites and excretion through urine, hair from a studied population in West Bengal, India

To evaluate the main intake source of arsenic by the villagers from arsenic-affected families in Jalangi and Domkol blocks in Mushidabad district, West Bengal-India, we determined the concentrations of arsenic in tube-well water and in food composites, mainly including vegetables and cereals collected from the surveyed families which were cultivated in that region. The daily dietary intakes of arsenic by the villagers were estimated and the excretions of arsenic through urine and hair were determined. The arsenic concentrations in hair and urine of the studied population living in mild (2.78 microg/L), moderate (30.7 microg/L) and high (118 microg/L) arsenic-affected families were 133, 1,391 and 4,713 microg/kg and 43.1, 244 and 336 microg/L, respectively. The linear regressions show good correlations between arsenic concentrations in water vs hair (r(2)=0.928, p<0.001) and water vs urine (r(2)=0.464, p<0.01). Approximately 29.4%, 58.1% and 62.1% of adult population from mild, moderate and high arsenic-affected families were suffering from arsenical skin manifestations. The mean arsenic concentrations of food composites (vegetables and cereals) in high arsenic-affected families are not significantly different from mild arsenic-affected families. The daily dietary intakes of arsenic from water and food composites of the studied population, living in high, moderate and mild arsenic-affected families were 568, 228 and 137 microg, respectively. The linear regressions show good correlations between arsenic concentrations in hair vs daily dietary intake (r(2)=0.452, p<0.001) and urine vs daily dietary intake (r(2)=0.134, p<0.001). The water for drinking contributed 6.07%, 26.7% and 58.1% of total arsenic in our study from mild, moderate and high arsenic-affected families. The result suggested that the contaminated water from high arsenic-affected families should be the main source for intake of arsenic. On contrary, the contribution of arsenic-contaminated food composites from mild and moderate arsenic-affected families might be the main source for intake of arsenic. The Food and Agriculture Organization/World Health Organization (FAO/WHO) provisional tolerable weekly intake (PTWI) values of arsenic in our study were 3.32, 5.75 and 12.9 microg/kg body weight/day from mild, moderate and high arsenic-affected families, respectively, which is higher than the recommended PTWI value of arsenic (2.1 microg/kg body weight/day).

Opposing effects of NaCl on reversibility and thermal stability of halophilic β-lactamase from a moderate halophile, Chromohalobacter sp. 560

Beta-lactamase from a moderately halophilic organism is expected to show salt-dependent stability. Here we examined the temperature-dependence of stability at different salt concentrations using circular dichroism (CD) and enzyme activity. NaCl showed opposing effects on melting temperature and reversibility of the thermal melting. Increasing NaCl concentration greatly increased the melting temperature from, e.g., 41 degrees C in the absence of NaCl to 61 degrees C in 3 M NaCl. Conversely, reversibility decreased from 92% to 0% in the corresponding NaCl solutions. When beta-lactamase was heated at different temperatures and NaCl concentrations, the activity recovery followed the reversibility, not the melting temperature. Heating beta-lactamase at 63 degrees C, slightly above the onset temperature of melting in 2 M NaCl and far above the melting in 0.2 M NaCl, showed a much greater recovery of activity in 0.2 M NaCl than in 2 M NaCl, again consistent with the reversibility of melting.

Efficient secretion of human lysozyme from the yeast, Kluyveromyces lactis

Efficient secretion of human lysozyme from the yeast, Kluyveromyces lactis, was achieved by using more stable vectors in the order of S11 replication origin-containing episomal vector < full-length K. lactis plasmid pKD1-containing vector < centromeric vector < chromosome-integrated vectors. Cells containing a PGK (phosphoglycerate kinase) promoter-driven integration vector grown in non-selective rich medium achieved the highest level of secretion, approximately 100 microg lysozyme secretion ml(-1) culture: this level was approximately 10-fold higher than that achieved by episomal vectors. An additional copy of the protein disulfide isomerase gene further facilitated the secretion.

Potent protecting effects of Catuaba (Anemopaegma mirandum) extracts against hydroperoxide-induced cytotoxicity

Ishigami et al. (Ishigami et al., 1998) reported that squalene monohydroperoxide (SQOOH) induced skin damage in hairless mice. Kohno and Takahashi (Kohno and Takahashi, 1993) reported that SQOOH induced cytotoxicity against Chinese hamster lung fibroblasts. We have already evaluated the efficacy of extracts obtained from Brazilian herbal medicines in protecting the normal human epidermis keratinocytes [NHEK(B)] against the cytotoxicity caused by SQOOH. The EtOAc extract was separated by silica-gel column chromatography into eight fractions. Fractions (Fr) 1,3 and 5 significantly protected rat basophilic leukemia (RBL-2H3) cells from the release of beta-hexosaminidase due to SQOOH. Additionally, Fr5-1 was most effective in a Gunze three-dimensional cultured human skin model (Vitrolife-skin) against the cytotoxicity due to SQOOH and the release of interleukin (IL)-2 and IL-4. The mixture of cinchonains Ia and Ib and the mixture of cinchonains IIa and IIb were isolated from Fr3 and Fr5-1, respectively. The results suggest that the addition of SQOOH caused the reduction in cell viability and the release of beta-hexosaminidase and cytokines as chemical mediators. The extract of Catuaba (Anemopaegma mirandum) prevented these toxic effects with the main active agents suggested to be cinchonains IIa and IIb.

Expression and purification of thioredoxin (TrxA) and thioredoxin reductase (TrxB) from Brevibacillus choshinensis

Brevibacillus choshinensis (formerly Bacillus brevis) is a protein-hyperproducing bacterium and has been used for commercial protein production. Here, we cloned thioredoxin (trxA) and thioredoxin reductase (trxB) genes from B. choshinensis, and expressed the gene products in Escherichia coli with an amino-terminal hexa-His-tag for purification and characterization. His-TrxA and His-TrxB were purified to homogeneity with one-step Ni-NTA affinity column chromatography, and the two recombinant proteins showed identical specific activity with or without removal of the amino-terminal His-tag, indicating that the extrasequence containing the hexa-His-tag did not affect their enzymatic activities. The E. coli expression system used here resulted in a 40-fold increase in production of His-TrxB protein compared to the level of native TrxB produced in non-recombinant B. choshinensis cells. TrxA and TrxB proteins with carboxy-terminal His-tag (TrxA-His and TrxB-His) were successfully expressed in B. choshinensis and were purified by Ni-NTA column chromatography. Co-expression of TrxA-His with recombinant human epidermal growth factor (hEGF) in B. choshinensis promoted the extracellular production of hEGF by up to about 200%.

Expression and purification of the Bacillus subtilis thioredoxin superfamily protein YkvV

Bacillus subtilis YkvV protein, an extracellular thioredoxin superfamily protein, was successfully expressed both in Brevibacillus choshinensis culture medium using an efficient promoter and the secretion signal of its surface layer protein, and in Escherichia coli cytoplasm with the amino-terminal His-tag (His-YkvV). His-YkvV was purified to homogeneity by Ni-NTA column. Both secreted YkvV and purified His-YkvV exhibited thiol-disulfide oxidoreductase activity.

Salt-inducible multidrug efflux pump protein in the moderately halophilic bacterium Chromohalobacter sp

It has been known that halophilic bacteria often show natural resistance to antibiotics, dyes, and toxic metal ions, but the mechanism and regulation of this resistance have remained unexplained. We have addressed this question by identifying the gene responsible for multidrug resistance. A spontaneous ofloxacin-resistant mutant derived from the moderately halophilic bacterium Chromohalobacter sp. strain 160 showed a two- to fourfold increased resistance to structurally diverse compounds, such as tetracycline, cefsulodin, chloramphenicol, and ethidium bromide (EtBr), and tolerance to organic solvents, e.g., hexane and heptane. The mutant produced an elevated level of the 58-kDa outer membrane protein. This mutant (160R) accumulated about one-third the level of EtBr that the parent cells did. An uncoupler, carbonyl cyanide m-chlorophenylhydrazone, caused a severalfold increase in the intracellular accumulation of EtBr, with the wild-type and mutant cells accumulating nearly equal amounts. The hrdC gene encoding the 58-kDa outer membrane protein has been cloned. Disruption of this gene rendered the cells hypersusceptible to antibiotics and EtBr and led to a high level of accumulation of intracellular EtBr. The primary structure of HrdC has a weak similarity to that of Escherichia coli TolC. Interestingly, both drug resistance and the expression of HrdC were markedly increased in the presence of a high salt concentration in the growth medium, but this was not observed in hrdC-disrupted cells. These results indicate that HrdC is the outer membrane component of the putative efflux pump assembly and that it plays a major role in the observed induction of drug resistance by salt in this bacterium.

Major outer membrane proteins in moderately halophilic eubacteria of generaChromohalobacter andHalomonas

Outer and inner membrane fractions of Chromohalobacter marismortui and Halomonas elongata were isolated by differential detergent solubilization, and profiles of membrane proteins, especially major outer membrane proteins, were analyzed. These type strains possessed one extremely abundant outer membrane protein which showed similarity in amino-terminal amino acid sequence with the outer membrane porin proteins in other Gram-negative bacteria. Three halophilic eubacterial strains isolated from saline environments were also characterized. Strains 160 and 43 were found to be Chromohalobacter spp. and strain 40 to be a Halomonas sp. by sequence analysis of their 16 S ribosomal RNA genes. Extremely abundant porin proteins with an apparent molecular mass of 49 kDa were found in Chromohalobacter sp.160 and Halomonas sp. 40, but no major outer membrane protein was detected in Chromohalobacter sp. 43, suggesting strain 43 was most likely a naturally defective porin mutant. Porin proteins from Chromohalobacter spp. and Halomonas spp. showed the same migration on SDS-polyacrylamide gel electrophoresis with or without heat-treatment, indicating that these porin proteins did not form a SDS-resistant trimeric structure, which was detected in most of the Gram-negative bacterial porin proteins.

Highly efficient renaturation of beta-lactamase isolated from moderately halophilic bacteria

Most, if not all, beta-lactamases reported to date are irreversibly denatured at 60-70 degrees C. Here, we found that a halophilic beta-lactamase from the moderately halophilic bacterium Chromohalobacter sp. 560 was highly stable against heat inactivation: it retained approximately 75% of its activity after boiling for 5 min in the presence of 0.2 M NaCl, suggesting that the protein either incompletely denatures during the boiling process or readily renatures upon cooling to the assay temperature. Circular dichroism showed a complete unfolding at 60 degrees C and a full reversibility, indicating that the observed activity after boiling is due to efficient refolding following heat denaturation. The enzyme showed optimal activity at 50-60 degrees C, indicating that an increase in activity with temperature offsets the thermal denaturation. The gene bla was cloned, and the primary structure of the enzyme was deduced to be highly abundant in acidic amino acid residues, one of the characteristics of halophilic proteins. Despite its halophilic nature, the enzyme refolds in low salt media after heat denaturation.

MRI of ectopic posterior pituitary bright spot with large adenomas: appearances and relationship to transient postoperative diabetes insipidus

MRI of large pituitary adenomas has revealed that a posterior pituitary bright spot (PPBS), comprising ADH-containing neurosecretory granules, is commonly ectopic before surgery and attached to the tip of the pituitary stalk late after surgery. Although the PPBS indicates functional integrity of the posterior lobe, transient diabetes insipidus (DI), caused by deficiency of ADH, is frequent early after surgery. We attempted to clarify how the shape, signal intensity and site of the PPBS before surgery are related to transient DI in the early postoperative period. We carried out MRI on 15 patients with a large adenoma and an ectopic PPBS before surgery and then within 1 week (early), 1-2 months (intermediate) and 6 or more months (late) after the operation. There were nine who had transient DI, which subsided by the intermediate study; none had permanent DI. Regardless of transient DI, the PPBS was visible, and its signal intensity was similar, on all postoperative studies. Although 11 did not change in shape, four showed a remarkable change from a flat shape before surgery to a rounded one postoperatively. On the intermediate MRI, the PPBS had descended to the level of the diaphragma as mass effect disappeared.

Cloning and expression of the ccdA-associated thiol-disulfide oxidoreductase (catA) gene from Brevibacillus choshinensis: stimulation of human epidermal growth factor production

Brevibacillus choshinensis (Bacillus brevis) is a protein-hyperproducing bacterium with a useful host-vector system for the production of recombinant proteins. Here, we cloned the ccdA-catA (cmacr;cdA āssociated thioredoxin-like tmacr;hiol-disulfide oxidoreductase) locus of B. choshinensis HPD31-S5. CatA protein (molecular weight, 19664) contains a thioredoxin-like motif, Cys-Gly-Pro-Cys. It was successfully expressed in B. choshinensis extracellularly ( approximately 100 microg x ml(-1) culture) using the secretion vector pNCMO2, and in Escherichia coli intracellularly ( approximately 350 microg x ml(-1) culture) with an amino-terminal His-tag. Both recombinant proteins showed thiol-disulfide oxidoreductase activity. Incubation of non-native human epidermal growth factor (hEGF) containing incorrect disulfide bonds with B. choshinensis cells secreting CatA protein resulted in the stimulation of the conversion of non-native hEGF to the native form. Furthermore, co-expression of CatA protein with recombinant hEGF in the B. choshinensis production system increased the yield of native hEGF.

Activation of halophilic nucleoside diphosphate kinase by a non-ionic osmolyte, trimethylamine N-oxide

The folding and activity of halophilic enzymes are believed to require the presence of salts at high concentrations. When the inactivated nucleoside diphosphate kinase (NDK) from extremely halophilic archaea was incubated with low salt media, no activity was regained over the course of 8 days. When it was incubated with approximately 2 M NaCl or 3 M KCl, however, it gradually regained activity. To our surprise, trimethylamine N-oxide (TMAO) also was able to induce activation at 4.0 M. The enzyme activity and secondary structure of refolded NDK in 4 M TMAO were comparable with those of the native NDK or the refolded NDK in 3.8 M NaCl. TMAO is not an electrolyte, meaning that the presence of concentrated salts is not an absolute requirement, and that charge shielding or ion binding is not a sole factor for the folding and activation of NDK. Although both NaCl and TMAO are effective in refolding NDK, the mechanism of their actions appears to be different: the effect of protein concentration and pH on refolding is qualitatively different between these two, and at pH 8.0 NDK could be refolded in the presence of 4 M TMAO only when low concentrations of NaCl are included.