Kinetic, structural and molecular docking studies on the inhibition of tyrosinase induced by arabinose

Tyrosinase plays a central role in biological pigment formation, and hence knowledge of tyrosinase catalytic mechanisms and regulation may have medical, cosmetic, and agricultural applications. We found in this study that arabinose significantly inhibited tyrosinase, and this was accompanied by conformational changes in enzyme structure. Kinetic analysis showed that arabinose-mediated inactivation followed first-order kinetics, and single and multiple classes of rate constants were measured. Arabinose displayed a mixed-type inhibitory mechanism with K(i)=0.22±0.07 mM. Measurements of intrinsic and ANS-binding fluorescence showed that arabinose induced tyrosinase to unfold and expose inner hydrophobic regions. We simulated the docking between tyrosinase and arabinose (binding energies were -26.28 kcal/mol for Dock6.3 and -2.02 kcal/mol for AutoDock4.2) and results suggested that arabinose interacts mostly with His61, Asn260, and Met280. The present strategy of predicting tyrosinase inhibition by simulation of docking by hydroxyl groups may prove useful in screening for potential tyrosinase inhibitors, as shown here for arabinose.     

Effects of osmolytes on human brain-type creatine kinase folding in dilute solutions and crowding systems

The effects of osmolytes on the unfolding and refolding process of recombinant human brain-type creatine kinase (rHBCK) were comparatively, quantitatively studied in dilute solutions and macromolecular crowding systems (simulated by 100g/L polyethylene glycol 2000), respectively. The results showed that the osmolytes, including glycerol, sucrose, dimethylsulfoxide, mannitol, inositol, and xylitol, could both protect the rHBCK from denaturation induced by 0.8M GdnHCl and aid in the refolding of denatured-rHBCK in macromolecular crowding systems. When we examined the effects of sucrose and xylitol on the parameters of residual activity, reaction kinetics and intrinsic fluorescence of rHBCK during unfolding, it was found that the protecting effects of osmolytes in a macromolecular crowding system were more significant compared with those in a dilute solution, which resulted in more residual activities, protected the conformational changes and greatly decreased the rates of both the fast and slow tracks. Regarding the effects of glycerol, sucrose and mannitol on the denatured-rHBCK refolding parameters of refolding yield, reaction kinetics and aggregation, the results indicated that the osmolytes could alleviate the aggregation of rHBCK during refolding in both dilute solutions and macromolecular crowding systems, and the refolding yields and reaction rates under macromolecular crowding environment could be increased by the addition of osmolytes, though higher yields were obtained in the dilute solution. For further insight, osmolyte docking simulations and rHBCK denaturation were conducted successfully and confirmed our experimental results. The predictions based on the docking simulations suggested that the deactivation of guanidine may be blocked by osmolytes because they share common binding sites on rHBCK, and the higher number of interactions with rHBCK by osmolytes than guanidine may be one of the causes of rHBCK refolding. In brief, the additive effects of the exclusive volume effect from the macromolecular crowding system and the osmophobic effects from the osmolytes resulted in better performance of the osmolytes in a macromolecular crowding system, which also led to a better understanding of protein folding in the intracellular environment.     

Method Optimization for Extracting High-Quality RNA From the Human Pancreas Tissue

Nucleic acid sequencing is frequently used to determine the molecular basis of diseases. Therefore, proper storage of biological specimens is essential to inhibit nucleic acid degradation. RNA isolated from the human pancreas is generally of poor quality because of its high concentration of endogenous RNase. In this study, we optimized the method for extracting high quality RNA from paired tumor and normal pancreatic tissues obtained from eight pancreatic cancer patients post-surgery. RNA integrity number (RIN) was checked to evaluate the integrity of RNA, we tried to extract the RNA with an RIN value of 8 or higher that allows for the latest genetic analysis. The effect of several parameters, including the method used for tissue lysis, RNAlater treatment, tissue weight at storage, and the time to storage after surgical resection, on the quantity and quality of RNA extracted was examined. Data showed that the highest quantity of RNA was isolated using a combination of manual and mechanical methods of tissue lysis. Additionally, sectioning the tissues into small pieces (<100 mg) and treating them with RNAlater solution prior to storage increased RNA stability. Following these guidelines, high quality RNA was obtained from 100% (8/8) of tumor tissues and 75% (6/8) of normal tissues. High-quality RNA was still stable under repeated freezing and thawing. The application of these results during sample handling and storage in clinical settings will facilitate the genetic diagnosis of diseases and their subsequent treatment.     

Allelopathic suppression of wheat and mustard byRumex dentatus ssp.klotzschianus

Laboratory studies were conducted to see the allelopathic suppression of wheat and mustard byRumex dentatus ssp.klotzschianus (Meissn) Rech. It was observed that aqueous extracts, rain leachates and litter from dried and fresh shoot and roots invariably inhibited the germination and seedling growth of both the crop species. Soil collected from beneathRumex dentatus also proved harmful for the germination and seedling growth. It is suggested thatRumex dentatus ssp.klotzschianus exhibits allelopathy against wheat and mustard.     

From the mouths of monkeys: detection of Mycobacterium tuberculosis complex DNA from buccal swabs of synanthropic macaques

Although the Mycobacterium tuberculosis complex (MTBC) infects a third of all humans, little is known regarding the prevalence of mycobacterial infection in nonhuman primates (NHP). For more than a century, tuberculosis has been regarded as a serious infectious threat to NHP species. Advances in the detection of MTBC open new possibilities for investigating the effects of this poorly understood pathogen in diverse populations of NHP. Here, we report results of a cross-sectional study using well-described molecular methods to detect a nucleic acid sequence (IS6110) unique to the MTBC. Sample collection was focused on the oral cavity, the presumed route of transmission of MTBC. Buccal swabs were collected from 263 macaques representing 11 species in four Asian countries and Gibraltar. Contexts of contact with humans included free ranging, pets, performing monkeys, zoos, and monkey temples. Following DNA isolation from buccal swabs, the polymerase chain reaction (PCR) amplified IS6110 from 84 (31.9%) of the macaques. In general, prevalence of MTBC DNA was higher among NHP in countries where the World Health Organization reports higher prevalence of humans infected with MTBC. This is the first demonstration of MTBC DNA in the mouths of macaques. Further research is needed to establish the significance of this finding at both the individual and population levels. PCR of buccal samples holds promise as a method to elucidate the mycobacterial landscape among NHP, particularly macaques that thrive in areas of high human MTBC prevalence.     

The stability of L-ATC hydrolase participating in L-cysteine production

Summary In the production of L-cysteine from D,L-ATC stability of the relevant enzymes produced byPseudomonas sp. was tested, and strategies to improve the stability of L-ATC hydrolase were investigated in view of water activity and ionic strength. Among the three enzymes which participate in L-cysteine production, i.e., ATC racemase, L-ATC hydrolase, and S-carbamyl-L-cysteine hydrolase, L-ATC hydrolase is the least stable. Various mixtures of salts and sorbitol were added to adjust the water activities of the tested solutions. As water activity decreased from 0.93 to 0.80, the stability of L-ATC hydrolase was sharply enhanced. In the absence of sorbitol the stability of L-ATC hydrolase increased in proportion to ionic strength. Even though enzyme stability was not good at a low ionic strength, it was enhanced by lowering water activity with addition of sorbitol. The half life of L-ATC hydrolase in sorbitol-salt mixtures increased by tenfold to twentyfold compared to that of a control.     

A monoclonal antibody specific for Candida albicans Als4 demonstrates overlapping localization of Als family proteins on the fungal cell surface and highlights differences between Als localization in vitro and in vivo

The Candida albicans agglutinin-like sequence (ALS) family encodes large cell surface glycoproteins that function in adhesion of the fungus to host and abiotic surfaces. Monoclonal antibodies (mAbs) specific for each Als protein were developed to study Als localization on the C. albicans surface. An anti-Als4 mAb demonstrated that Als4 covers the surface of yeast cells, with a greater abundance of Als4 on cells grown at 30 °C compared to 37 °C. On germ tubes, Als4 is localized in a restricted area proximal to the mother yeast. Immunolabeling with several anti-Als mAbs showed overlapping localization of Als1 and Als4 on yeast cells and Als1, Als3 and Als4 on germ tubes. Overlapping localization of Als proteins was also observed on yeast and hyphae recovered from mouse models of disseminated and oral candidiasis. Differences between Als localization in vivo and in vitro suggested changes in regulation of Als production in the host compared to the culture flask. Characterization with the anti-Als mAbs reveals the simultaneous presence and differences in relative abundance of Als proteins, creating an accurate image of Als representation and localization that can be used to guide conclusions regarding individual and collective Als protein function.