Modification of the transglucosylation properties of α-glucosidases from Aspergillus oryzae and Aspergillus sojae via a single critical amino acid replacement.

We constructed enzyme variants of the α-glucosidases from Aspergillus oryzae (AoryAgdS) and Aspergillus sojae (AsojAgdL) by mutating the amino acid residue at position 450. AoryAgdS_H450R acquired the ability to produce considerable amounts of α-1,6-transglucosylation products, whereas AsojAgdL_R450H changed to produce more α-1,3- and α-1,4-transglucosylation products than α-1,6-products. The 450th amino acid residue is critical for the transglucosylation of these α-glucosidases.

Analysis of Transglucosylation Products of Aspergillus niger α-Glucosidase that Catalyzes the Formation of α-1,2- and α-1,3-Linked Oligosaccharides.

According to whole-genome sequencing, Aspergillus niger produces multiple enzymes of glycoside hydrolases (GH) 31. Here we focus on a GH31 α-glucosidase, AgdB, from A. niger . AgdB has also previously been reported as being expressed in the yeast species, Pichia pastoris ; while the recombinant enzyme (rAgdB) has been shown to catalyze tranglycosylation via a complex mechanism. We constructed an expression system for A. niger AgdB using Aspergillus nidulans . To better elucidate the complicated mechanism employed by AgdB for transglucosylation, we also established a method to quantify glucosidic linkages in the transglucosylation products using 2D NMR spectroscopy. Results from the enzyme activity analysis indicated that the optimum temperature was 65 °C and optimum pH range was 6.0-7.0. Further, the NMR results showed that when maltose or maltopentaose served as the substrate, α-1,2-, α-1,3-, and small amount of α-1,1-ß-linked oligosaccharides are present throughout the transglucosylation products of AgdB. These results suggest that AgdB is an α-glucosidase that serves as a transglucosylase capable of effectively producing oligosaccharides with α-1,2-, α-1,3-glucosidic linkages.

Microbicidal effects of weakly acidified chlorous acid water against feline calicivirus and Clostridium difficile spores under protein-rich conditions.

Sanitation of environmental surfaces with chlorine based-disinfectants is a principal measure to control outbreaks of norovirus or Clostridium difficile. The microbicidal activity of chlorine-based disinfectants depends on the free available chlorine (FAC), but their oxidative potential is rapidly eliminated by organic matter. In this study, the microbicidal activities of weakly acidified chlorous acid water (WACAW) and sodium hypochlorite solution (NaClO) against feline calcivirus (FCV) and C. difficile spores were compared in protein-rich conditions. WACAW inactivated FCV and C. difficile spores better than NaClO under all experimental conditions used in this study. WACAW above 100 ppm FAC decreased FCV >4 log10 within 30 sec in the presence of 0.5% each of bovine serum albumin (BSA), polypeptone or meat extract. Even in the presence of 5% BSA, WACAW at 600 ppm FAC reduced FCV >4 log10 within 30 sec. Polypeptone inhibited the virucidal activity of WACAW against FCV more so than BSA or meat extract. WACAW at 200 ppm FAC decreased C. difficile spores >3 log10 within 1 min in the presence of 0.5% polypeptone. The microbicidal activity of NaClO was extensively diminished in the presence of organic matter. WACAW recovered its FAC to the initial level after partial neutralization by sodium thiosulfate, while no restoration of the FAC was observed in NaClO. These results indicate that WACAW is relatively stable under organic matter-rich conditions and therefore may be useful for treating environmental surfaces contaminated by human excretions.

The contribution of peripheral stem-loops to the catalytic activity of archaeal RNase P RNA from Pyrococcus horikoshii OT3.

We investigated the contribution of peripheral stem-loops to the catalytic activity of an archaeal RNase P RNA, PhopRNA, from Pyrococcus horikoshii OT3. PhopRNA mutants, in which the stem-loops were individually deleted, were prepared and characterized with respect to precursor tRNA (pre-tRNA) cleavage activity in the presence of five RNase P proteins. All the mutants retained the activity to some extent, indicating that they are moderately implicated in catalysis. Further characterization suggested that the stem-loops serve largely as binding sites for the proteins, and that their interactions are predominantly involved in stabilization of the active conformation of PhopRNA.

Effect of apple intake on fecal microbiota and metabolites in humans.

The effects of apple intake on the fecal flora, water content, pH, and metabolic activities in eight healthy volunteers and the utilization of apple pectin in vitro were investigated. Although several isolates of Bifidobacterium, Lactobacillus, Enterococcus, and the Bacteroides fragilis group utilized apple pectin, most isolates of Escherichia coli, Collinsela aerofaciense, Eubacterium limosum, and Clostridium perfringens could not. When fecal samples from healthy adults were incubated in liquid broth with apple pectin present or absent, the numbers of Bifidobacterium and Lactobacillus in the former were higher than those in the later. After the intake of apples (2 apples a day for 2 weeks) by eight healthy adult humans, the number of bifidobacteria in feces increased (p < 0.05 on day 7 and p < 0.01 on day 14 of the intake period), and the numbers of Lactobacillus and Streptococcus including Enterococcus tended to increase. However, lecithinase-positive clostridia, including C. perfringens, decreased (p < 0.05), and Enterobacteriaceae and Pseudomonas tended to decrease. Moreover, the concentrations of fecal acetic acid tended to increase on apple intake. The fecal ammonia concentration showed a tendency to reduce and fecal sulfide decreased (p < 0.05) on apple intake. These findings indicate that apple consumption is related to an improved intestinal environment, and apple pectin is one of the effective apple components improving the fecal environment.

Identification of nucleotide residues essential for RNase P activity from the hyperthermophilic archaeon Pyrococcus horikoshii OT3.

Ribonuclease P (RNase P) is involved in the processing of the 5' leader sequence of precursor tRNA (pre-tRNA). We have found that RNase P RNA (PhopRNA) and five proteins (PhoPop5, PhoRpp21, PhoRpp29, PhoRpp30, and PhoRpp38) reconstitute RNase P activity with enzymatic properties similar to those of the authentic ribozyme from the hyperthermophilic archaeon Pyrococcus horikoshii OT3. We report here that nucleotides A40, A41, and U44 at helix P4, and G269 and G270 located at L15/16 in PhopRNA, are, like the corresponding residues in Esherichia coli RNase P RNA (M1RNA), involved in hydrolysis by coordinating catalytic Mg(2+) ions, and in the recognition of the acceptor end (CCA) of pre-tRNA by base-pairing, respectively. The information reported here strongly suggests that PhopRNA catalyzes the hydrolysis of pre-tRNA in approximately the same manner as eubacterial RNase P RNAs, even though it has no enzymatic activity in the absence of the proteins.

Scavenging activity of indole compounds against cisplatin-induced reactive oxygen species.

The antioxidant effects of indole compounds such as melatonin (MLT), tryptophan, and serotonin, on cisplatin (cis-diaminedichloroplatinum, or CDDP)-induced reactive oxygen species (ROS) generation were examined by electron spin resonance (ESR). In addition, DNA fragmentation by CDDP-induced ROS and the effect of MLT on it were analyzed in primary cultures of rat renal tubular epithelial cells. MLT and serotonin had scavenging effects on CDDP-induced hydroxy radicals (*OH), and the scavenging activity of MLT was higher than that of serotonin. The exposure of primary-cultured renal tubular cells to CDDP caused severe cytotoxicity. Tryptophan, serotonin, and 6-OH-MLT did not reduce the CDDP-induced cytotoxicity, whereas MLT did. CDDP exposure induced DNA fragmentation in primary-cultured renal tubular cells, but the simultaneous administration of MLT inhibited the DNA fragmentation. These results indicate that MLT inhibits CDDP-induced cytotoxicity by directly scavenging *OH, and that MLT markedly reduces renal cytotoxicity and DNA fragmentation caused by CDDP-induced ROS in vitro.

Characterization of the archaeal ribonuclease P proteins from Pyrococcus horikoshii OT3.

Ribonuclease P (RNase P) is a ribonucleoprotein complex involved in the processing of the 5'-leader sequence of precursor tRNA (pre-tRNA). Our earlier study revealed that RNase P RNA (pRNA) and five proteins (PhoPop5, PhoRpp38, PhoRpp21, PhoRpp29, and PhoRpp30) in the hyperthermophilic archaeon Pyrococcus horikoshii OT3 reconstituted RNase P activity that exhibits enzymatic properties like those of the authentic enzyme. In present study, we investigated involvement of the individual proteins in RNase P activity. Two particles (R-3Ps), in which pRNA was mixed with three proteins, PhoPop5, PhoRpp30, and PhoRpp38 or PhoPop5, PhoRpp30, and PhoRpp21 showed a detectable RNase P activity, and five reconstituted particles (R-4Ps) composed of pRNA and four proteins exhibited RNase P activity, albeit at reduced level compared to that of the reconstituted particle (R-5P) composed of pRNA and five proteins. Time-course analysis of the RNase P activities of R-4Ps indicated that the R-4Ps lacking PhoPop5, PhoRpp21, or PhoRpp30 had virtually reduced activity, while omission of PhoRpp29 or PhoRpp38 had a slight effect on the activity. The results indicate that the proteins contribute to RNase P activity in order of PhoPop5 > PhoRpp30 > PhoRpp21 >> PhoRpp29 > PhoRpp38. It was further found that R-4Ps showed a characteristic Mg2+ ion dependency approximately identical to that of R-5P. However, R-4Ps had optimum temperature of around at 55 degrees C which is lower than 70 degrees C for R-5P. Together, it is suggested that the P. horikoshii RNase P proteins are predominantly involved in optimization of the pRNA conformation, though they are individually dispensable for RNase P activity in vitro.

A fifth protein subunit Ph1496p elevates the optimum temperature for the ribonuclease P activity from Pyrococcus horikoshii OT3.

Ribonuclease P (RNase P) is a ribonucleoprotein complex involved in the processing of the 5' leader sequence of precursor tRNA. We previously found that the reconstituted particle (RP) composed of RNase P RNA and four proteins (Ph1481p, Ph1601p, Ph1771p, and Ph1877p) in the hyperthermophilic archaeon Pyrococcus horikoshii OT3 exhibited the RNase P activity, but had a lower optimal temperature (around at 55 degrees C), as compared with 70 degrees C of the authentic RNase P from P. horikoshii [Kouzuma et al., Biochem. Biophys. Res. Commun. 306 (2003) 666-673]. In the present study, we found that addition of a fifth protein Ph1496p, a putative ribosomal protein L7Ae, to RP specifically elevated the optimum temperature to about 70 degrees C comparable to that of the authentic RNase P. Characterization using gel shift assay and chemical probing localized Ph1496p binding sites on two stem-loop structures encompassing nucleotides A116-G201 and G229-C276 in P. horikoshii RNase P RNA. Moreover, the crystal structure of Ph1496p was determined at 2.0 A resolution by the molecular replacement method using ribosomal protein L7Ae from Haloarcula marismortui as a search model. Ph1496p comprises five alpha-helices and a four stranded beta-sheet. The beta-sheet is sandwiched by three helices (alpha1, alpha4, and alpha5) at one side and two helices (alpha2 and alpha3) at other side. The archaeal ribosomal protein L7Ae is known to be a triple functional protein, serving as a protein component in ribosome and ribonucleoprotein complexes, box C/D, and box H/ACA. Although we have at present no direct evidence that Ph1496p is a real protein component in the P. horikoshii RNase P, the present result may assign an RNase P protein to L7Ae as a fourth function.

The fermentation of different dietary fibers is associated with fecal clostridia levels in men.

Only a few reports have compared the fermentation of pectin and cellulose using the hydrogen-breath test, and no studies have examined the relation between the hydrogen breathing pattern and colonic microflora. Using breath-hydrogen measurements, we investigated whether different dietary fibers (DFs) were fermented differently and whether there were individual differences after ingestion of the same DF; we also examined the relation between individual fecal microflora and the fermentation of DF. Results of hydrogen tests in 14 men were compared after they had ingested 20 g of pectin, 20 g of cellulose, or 6 g of lactulose (a DF-like substance). We examined the relation between the breath hydrogen results and the subjects' fecal microflora. We defined significant fermentation (i.e., positive cases) as a continuous rise in hydrogen in the expiratory air of >19 ppm. The subjects were divided into 3 groups according to their hydrogen breath test pattern, i.e., positive for lactulose and pectin (Group LP, n = 4); positive for lactulose alone (Group L, n = 7); and negative for pectin, cellulose, and lactulose (Group N, n = 3). Individual differences were noted in subjects from Group LP and Group L. The detection frequency of lecithinase-negative clostridia was higher in Group LP than in the other groups (P < 0.05), and the detection frequency and the number of lecithinase-positive clostridia were higher in Groups LP and L than in Group N (P < 0.05). These findings suggest that the Clostridium species are associated with hydrogen production. The hydrogen breath test results of DFs depend on both the type of DF and the individual colonic microflora. The amount and constitution of colonic microflora might be predicted by the hydrogen-breath test using different DFs.

Melatonin prevents the increase in hydroxyl radical-spin trap adduct formation caused by the addition of cisplatin in vitro.

We studied the generation of reactive oxygen species (ROS) caused by cisplatin administration and the preventive effect of melatonin, the main secretory product of the pineal gland, on the reaction in vitro using electron spin resonance spectroscopy. Cisplatin induced generation of the hydroxyl radical (OH*) in phosphate buffer in pH 7.4 as a dose-dependent manner. However, OH* was not generated in phosphate buffer containing chloride ions at concentration exceeding 120 mM. The induction of OH. production by cisplatin was completely inhibited by the addition of melatonin, but not by the addition of 6-hydroxymelatonin, which is a hepatic metabolite of melatonin. Furthermore, melatonin was the most effective agent for preventing of OH* formation among various well-known antioxidants including mannitol and reduced glutathione. These results indicate that melatonin may scavenge OH. directly and thereby prevent renal tissue damage caused by OH* produced in response to cisplatin treatment.