The thermal and storage stability of bovine haemoglobin by ultraviolet-visible and circular dichroism spectroscopies

The effects of temperature,pH and long-term storage on the secondary structure and conformation changes of bovine haemoglobin（bHb） were studied using circular dichroism（CD） and ultraviolet-visible（UV-vis） spectroscopies.Neural network software was used to deconvolute the CD data to obtain the fractional content of the five secondary structures.The storage stability of bHb solutions in pH 6,7 and8 buffers was significantly higher at 4 ℃ than at 23 ℃ for the first 3 days.A complete denaturation of bHb was observed after 40 days irrespective of storage temperature or pH.The bHb solutions were also exposed to heating and cooling cycles between 25 and 65 ℃ and structural changes were followed by UVvis and CD spectroscopies.These experiments demonstrated that α-helix content of bHb decreased steadily with the increasing temperature above 35 ℃ at all pH values.The loss in a-helicity and gain in random coil conformations was pH-dependent and the greatest under alkaline conditions.Furthermore,there was minimal recovery of the secondary structure content upon cooling to 25 ℃.The use of bHb as a model drug is very common and this study elucidates the significance of storage and processing conditions on its stability.

Characterization of Interaction Between Raltitrexed and Bovine Serum Albumin by Optical Spectroscopic Techniques

The interaction of raltitrexed（RTX） with bovine serum albumin（BSA） was investigated by steady state/lifetime fluorescence spectroscopy and circular dichroism（CD） spectroscopy under the simulative physiological conditions.The results of fluorescence titration reveal that RTX could strongly quench the intrinsic fluorescence of BSA via a static quenching procedure.The obtained binding constant K A of RTX with BSA was 478630 and 44259 L/mol at 298 and 310 K,respectively.According to van＇t Hoff equation,the thermodynamic parameters ΔH,ΔG and ΔS were calculated,indicating that hydrophobic forces were the predominant intermolecular forces in stabilizing the complex.The binding process was a spontaneous process,in which Gibbs free energy change was negative.According to F rster＇s non-radioactive energy transfer theory,the distance r between donor（BSA） and acceptor（RTX） was 3.82 nm,suggesting that the energy transfer from BSA to RTX occurred with high probability.Displacement experiment and the number of binding sites calculation confirmed that RTX could bind to the site-I of BSA.Furthermore,the effects of pH and some metal ions on the interaction of RTX with BSA were also investigated.The results of synchronous fluorescence and CD spectra show that the RTX-BSA binding induced conformational changes in BSA.

The Streptococcus agalactiae Ribose Binding Protein B (RbsB) Mediates Quorum Sensing Signal Uptake via Interaction with Autoinducer-2 Signals

Understanding aquatic pathogen in sediments or aquacultural water is crucial to protect public health from soilborne and waterborne diseases.Quorum sensing(QS)was increasingly reported in biological wastewater treatment processes because of their inherent roles in biofilm development,bacterial aggregation and so on.The widely QS signals was Antoinducer-2(AI-2),primarily involved to allow the possibility of interspecies communication.However,the cellular components that mediate the response of Streptococcus agalactiae to AI-2 have not been fully characterized.Analysis of the complete genome sequence of S.agalactiae indi-cated that its RbsB protein has similarity to Escherichia coli LsrB and Aggregatibacter actinomycetemcomitans RbsB proteins that bind AI-2.We hypothesized that RbsB protein mediates quorum sensing signal uptake via interaction with AI-2.To evaluate the regulatory effect of RbsB on QS system,the recombinant plasmid pGEX-6p-1-RbsB was constructed and RbsB protein was purified with GST-tag.To further elucidate the role of RbsB protein binding to DPD(AI-2 precursor dihydroxypentanedione),the systemati-cally throughput circular dichroism(CD)spectroscopy,isothermal titration calorimetry200(ITC200)and molecular docking methods were employed.The high expression of soluble RbsB protein with molecular weight of 33 kDa was obtained.The thermodynamics results(ΔH<0,ΔS<0,ΔG<0)with ITC determination indicated that the binding process between DPD and RbsB was exothermic and spontaneous,with hydrogen bonds and van der Waals forces as the main binding forces.Obviously,DPD can be more easily combined with RbsB in a dose-dependent manner,suggesting that RbsB was changed in the microenvironment of DPD when the DPD concentration was between 0.8-1.0mmolL−1 and reaching the maximum binding amount.According to molecular docking,3 hydrophobic residues involved in DPD and RbsB protein stable binding were be found,and also hydrogen bonding plays a key role in the formation of the new complex.RbsB efficiently inhibited V.harveyi bioluminescence induced by both S.agalactiae AI-2 and V.harveyi AI-2 in a dose-dependent manner.However,our results suggest that RbsB may play a role in the response of S.agalactiace to AI-2.

Detection and Comparison of Structure and Function of Wild-type Pneumolysin and Its Novel Mutant PIyM2

Here is reported a novel pneumolysin（Ply） mutant（PlyM2） that addresses a long-standing problem for vaccine development in this field： detoxification of Ply in the premise of retaining antigenic integrity. Structure and function of wild-type Ply（PIyWT） and PIyM2 mutants were detected and compared. Their structures were not signi- ficantly different according to the analysis by thermal-dependent fluorescence spectroscopy and circular dichroism spectroscopy. PlyM2 was confirmed to have lost hemolytic activity and yet could induce neutralizing antibodies to prevent in vitro hemolysis by PIyWT and Streptococcus pneumoniae（S, pneumoniae）. These results give support to PIyM2 to be a new protein antigen for inclusion in the development of an effective pneumocoecal multiprotein vaccine.