Social Detachment Influenced Muscle Mass and Strength during the COVID-19 Pandemic in Japanese Community-Dwelling Older Women

Social detachment due to coronavirus disease (COVID-19) has caused a decline in physical activity, leading to sarcopenia and frailty in older adults. This study aimed to compare muscle mass, strength, and function values in older women before and after the first wave of the COVID-19 pandemic (April-May 2020). Furthermore, changes in muscle measures across women who experienced different levels of impact on their social participation due to the COVID-19 pandemic were examined. Muscle mass (total, trunk, and appendicular muscle), grip strength, oral motor skills, social interactions (social network and participation), and social support were assessed in 46 Japanese community-dwelling older women (mean, 77.5 y; range 66-93 y) before and after the first wave of the COVID-19 pandemic. Trunk muscle mass significantly decreased after the first wave of the pandemic. When comparing changed values between the enhanced/maintained and reduced group during the pandemic, significant group difference was observed in trunk muscular mass, grip strength, and oral motor skills. Intriguingly, those who enhanced social participation had a positive change of grip strength values, showing that social participation might influence muscle function during the COVID-19 pandemic.

Life-Long Wheel Running Attenuates Age-Related Fiber Loss in the Plantaris Muscle of Mice: a Pilot Study

The purpose of this study was to investigate whether long-term wheel running would attenuate age-related loss of muscle fiber. Male ICR mice were divided into young (Y, n=12, aged 3 months), old-sedentary (OS, n=5, aged 24 months), and old-exercise (OE, n=6, aged 24 months) groups. The OE group started spontaneous wheel running at 3 months and continued until 24 months of age. Soleus and plantaris muscles were fixed in 4% paraformaldehyde buffer. The fixed muscle was digested in a 50% NaOH solution to isolate single fiber and then fiber number was quantified. The masses of the soleus and plantaris muscles were significantly lower at 24 months than at 3 months of age, and this age-related difference was attenuated by wheel running (P<0.05). Soleus muscle fiber number did not differ among the groups. In the plantaris muscle, the fiber number in the OS group (1 288±92 fibers) was significantly lower than in the Y group (1 874±93 fibers), and this decrease was attenuated in the OE group (1 591±80 fibers) (P<0.05). These results suggest that age-related fiber loss occurs only in the fast-twitch fiber-rich muscle of mice, and that life-long wheel running exercise can prevent this fiber loss.

Thermoelectric Properties of AgBiTe2-Ag2Te Composite

We prepared composite materials of AgBiTe2 with several contents of Ag2Te small-size grains for applications to thermoelectric devices. By enhancing long-wavelength phonon scattering at the grain boundaries, lattice thermal conductivity (thermal conductivity due to lattice vibrations) decreased 30% and thus the thermoelectric characteristics were significantly improved.

Effects of heating procedures on deoxynivalenol, nivalenol and zearalenone levels in naturally contaminated barley and wheat

The influence of heating temperature and time on deoxynivalenol (DON), nivalenol (NIV) and zearalenone (ZEA) contents in naturally co-contaminated barley and wheat was investigated intending to establish the basis for a decontamination model of Fusarium mycotoxins in cereals. The standard toxins and whole barley powder samples were heated in a convection oven at 140, 160, 180, 200, or 220 degrees C, and kernel subsamples (200 g each) were roasted in an experimental rotary gas-fired roaster at 150, 180 or 220 degrees C. All treatments resulted in a time-temperature-dependent decomposition of the toxins; the logarithm of the toxin remaining % presented a linear relationship with heating time. The lines equations were used to estimate the half (H) and decimal (D) decomposition times (time required to destroy 50 or 90% of the toxin, respectively). DON and NIV H and D decomposition times were similar and 50% shorter for heated standards than for whole barley powder. ZEA standard values were considerably longer, while whole barley powder values were comparable with those of DON and NIV. At 220 degrees C, D decomposition times of DON, NIV and ZEA heated standards were 11, 10 and 85 min, respectively, while the values obtained in whole barley powder were the same for the three toxins (25 min). The determination of H and D decomposition values constitutes a basis to understand the heating stability nature of each toxin.

Elucidation of the relationship between enzyme activity and internal motion using a lysozyme stabilized by cavity-filling mutations

We investigated the activity and the internal motions of a stabilized mutant hen lysozyme (HEL) in which the residues M12 and L56 were mutated to L and F, respectively (LF mutant HEL). The result of the activity measurements against glycol chitin at various temperatures suggested that the temperature dependence of the activity of LF mutant HEL shifted to the high-temperature side compared with that of wild-type HEL. The detailed internal motions of LF mutant HEL in the absence and presence of a substrate analogue, (NAG)3, were examined by model-free analysis at 35 degrees C. The results showed that the internal motions of LF mutant HEL in the presence of (NAG)3 were drastically restricted compared with those in wild-type HEL. Our findings thus suggested that the mutation to the stabilized lysozyme restricted internal motions required for the enzymatic reaction.

Evidence for a novel racemization process of an asparaginyl residue in mouse lysozyme under physiological conditions

We examined chemical reactions in mouse lysozyme after incubation under physiological conditions (pH 7 and 37 degrees C). After incubation for 8 weeks, racemization was observed specifically at Asn127 among the 19 Asp/Asn residues in mouse lysozyme. Furthermore, analysis of the primary structure showed that the racemized residue was not Asp, but Asn, which demonstrates that deamidation and isomerization did not occur. These results mean that this racemization occurs without forming a succinimide intermediate. This is the first example of D-asparaginyl formation in a protein occurring during the racemization process under physiological conditions.

Identification of the region in Escherichia coli DnaA protein required for specific recognition of the DnaA box

DnaA protein binds specifically to a 9-base- pair motif called the DnaA box. Domain IV comprises 94 amino acid residues and is required for DNA binding. Using nuclear magnetic resonance analysis, we investigated the interaction between DnaA domain IV and both a DnaA box and a non-specific oligonucleotide that has a reduced affinity for DnaA. The 1H-15N HSQC spectrum of DnaA domain IV showed prominent chemical shift perturbations on six residues (Arg399, Ala404, Leu422, Asp433, Thr435 and Thr436) in the presence of the DnaA box. Through homology modeling, we located all of these residues on one side surface of the DnaA domain IV molecule. Moreover, we compared the chemical shift perturbation of the 1H-15N HSQC spectrum in the presence of the DnaA box with that in the presence of a non-specific oligonucleotide, and the results suggested that Leu422 imparts specificity in binding with the DnaA box.

A small chimerically bifunctional monomeric protein: Tapes japonica lysozyme

The lysozyme of the marine bilave Tapes japonica (13.8 kDa) is a novel protein. The protein has 46% homology with the destabilase from medicinal leech that has isopeptidase activity. Based on these data, we confirmed hydrolysis activity of T. japonica lysozyme against three substrates: L-gamma-Glu-pNA, D-gamma-Glu-pNA, and epsilon-(gamma-Glu)-L-Lys. The optimal pH of chitinase and isopeptidase activity was 5.0 and 7.0, respectively. The isopeptidase activity was inhibited with serine protease inhibitor, but the lytic and chitinase activities were not. Moreover, only isopeptidase activity is decreased by lyophilization, but lytic and chitinase activities were not. We conclude that T. japonica lysozyme expresses isopeptidase and chitinase activity at different active sites.

Solution structure and activity of mouse lysozyme M

The three-dimensional structure of mouse lysozyme M, glycoside hydrolase, with 130 amino acids has been determined by heteronuclear NMR spectroscopy. We found that mouse lysozyme M had four alpha-helices, two 3(10)helices, and a double- and a triple-stranded anti-parallel beta-sheet, and its structure was very similar to that of hen lysozyme in solution and in the crystalline state. The pH activity profile of p-nitrophenyl penta N-acetyl-beta-D-chitopentaoside hydrolysis by mouse lysozyme M was similar to that of hen lysozyme, but the hydrolytic activity of mouse lysozyme M was lower. From analyses of binding affinities of lysozymes to a substrate analogue and internal motions of lysozymes, we suggest that the lower activity of mouse lysozyme M was due to the larger dissociation constant of its enzyme-substrate complex and the restricted internal backbone motions in the molecule.

Evidence for an initiation site for hen lysozyme folding from the reduced form using its dissected peptide fragments

We prepared two dissected fragments of hen lysozyme and examined whether or not these two fragments associated to form a native-like structure. One (Fragment I) is the peptide fragment Asn59-homoserine-105 containing Cys64-Cys80 and Cys76-Cys94. The other (Fragment II) is the peptide fragment Lys1-homoserine-58 connected by two disulfide bridges, Cys6-Cys127 and Cys30-Cys115, to the peptide fragment Asn106-Leu129. It was found that the Fragment I immobilized in the cuvette formed an equimolar complex with Fragment II (K(d) = 3.3x10(-4) M at pH 8 and 25 degrees C) by means of surface plasmon resonance. Moreover, from analyses by circular dichroism spectroscopy and ion-exchange chromatography of the mixture of Fragments I and II at pH 8 under non-reducing conditions, it was suggested that these fragments associated to give the native-like structure. However, the mutant Fragment I in which Cys64-Cys80 and Cys76-Cys94 are lacking owing to the mutation of Cys to Ala, or the mutant fragment in which Trp62 is mutated to Gly, did not form the native-like species with Fragment II, because the mutant Fragment I derived from mutant lysozymes had no local conformation due to mutations. Considering our previous results where the preferential oxidation of two inside disulfide bonds, Cys64-Cys80 and Cys76-Cys94, occurred in the refolding of the fully reduced Fragment I, we suggest that the peptide region corresponding to Fragment I is an initiation site for hen lysozyme folding.

Beta-cyclodextrin inhibits the sweet taste suppressing activity of gurmarin by the formation of an inclusion complex with aromatic residues in gurmarin

Our recent study in mice revealed that the inhibitory activity of gurmarin on the sweet taste responses was reduced significantly by the presence of beta-cyclodextrin (beta-CD). To investigate the mechanism involved in the action of beta-CD, physicochemical experiments were performed on the interaction of CDs with gurmarin examining the effect of CDs on the UV absorption spectrum of gurmarin and on the elution behavior in gel filtration (or exclusion) chromatography. Among the three kinds of cyclodextrins tested, beta-CD induced significant changes in the UV absorption spectrum of gurmarin that were characteristic of those found in the inclusion complex formation of tyrosine and tryptophan with beta-CD. The abnormal retention behavior of gurmarin in gel filtration resulting from hydrophobic interaction with the gel matrix reverted to normal in the presence of beta-CD in the elution buffer. These results suggest that the unique domain of gurmarin, in which five aromatic amino acid residues are all directed outwardly and form a hydrophobic cluster, is a possible site of interaction with the gurmarin-sensitive sweet taste receptor molecules in rodents.

Aggregation and chemical reaction in hen lysozyme caused by heating at pH 6 are depressed by osmolytes, sucrose and trehalose

We examined the effects of osmolytes, sucrose and trehalose, on the deterioration of hen lysozyme as a model protein. Sucrose and trehalose depressed the aggregation of lysozyme molecules caused by heating at 100 degrees C at pH 6. Since lysozyme was fully denatured under these conditions, the effects of sucrose and trehalose on the denatured state of lysozyme were investigated using reduced S-alkylated lysozyme, a model of denatured hen lysozyme. From analyses of circular dichroism spectra and fluorescence spectra, sucrose and trehalose were found to induce alpha-helical conformations and some tertiary structures around tryptophan residues in the reduced S-alkylated lysozyme. Moreover, these compounds also depressed chemical reactions such as deamidation and racemization, which often cause the deterioration of proteins, on the reduced S-alkylated lysozyme. Therefore, the data suggest that sucrose and trehalose have a propensity to depress such deterioration as the aggregation of protein molecules or chemical reactions in proteins by inducing some tertiary structures (including alpha-helical structures) in the polypeptide chain.

Thermostability of doubly glycosylated recombinant lysozyme

We prepared a lysozyme mutant (Q41S/R61S) introducing Asn-type glycosylation signal sites by yeast expression system. On purification by cation exchange column at pH 7, three fractions were obtained. Peptide mapping and mass-spectrometry showed the fractions were the derivatives glycosylated at both Asn39 and Asn59, at only Asn39, and not glycosylated. It was revealed that the processing of Asn-linked oligosaccharide at Asn39 and Asn59 occurred independently in yeast cells. The denaturation temperatures of these derivatives by differential scanning calorimetry were 76.0, 68.8, and 67.5 degrees C at pH 3, respectively. The stabilization of glycosylated lysozyme depends on the degree of glycosylation. We concluded that stabilized proteins can be constructed by glycosylation at proper sites. Thermodynamic stabilization by the artificial double glycosylations on a protein has not yet been reported.

A single amino acid substitution in a self protein is sufficient to trigger autoantibody response

We determined if a single amino acid substitution in a self protein causes autoantibody responses. Mouse lysozyme (ML) was used as a model self protein, and a mutant ML (F57L ML) was prepared by replacing 57Phe of ML to Leu, an approach which resulted in introducing into ML the immunogenic sequence of peptide 50-61 of hen egg lysozyme (HEL) restricted to I-A(k) MHC class II molecule. We found that F57L ML but not native ML primed HEL specific T cells and triggered ML specific autoantibody responses in B10.A and C3H mice (I-A(k), I-E(k)). Peptide regions, ML 14-69 and ML 98-130, were major epitopes of autoantibodies in both strains of mice. These findings indicate that a single amino acid substitution in self proteins can cause an autoantibody response when the mutated region is presented by MHC class II molecules and recognized by T cells.

Tolerance of point substitution of methionine for isoleucine in hen egg white lysozyme

X-ray structure determination of proteins by using the multiple-wavelength anomalous dispersion method targeting selenomethionine is now widely employed. Isoleucine was examined for the second choice of the substitution of methionine next to leucine. We performed a systematic mutational study of the substitutions of methionine for isoleucine. All mutated lysozymes were less stable than the wild-type by about 1 kcal/mol and it is suggested that this instability was caused by the change in residual hydrophobicity from isoleucine to methionine. The X-ray structures of all mutant lysozymes were very similar to that of the wild-type. In addition, both the accessible surface areas and the conformation of the side chain of methionine in all mutant lysozymes were similar to those of the side chain at the respective isoleucine in the wild-type. Therefore, it is suggested that the mutation from isoleucine to methionine in a protein can be considered as a "safe" substitution.

The relationship between the aggregational state of the amyloid-beta peptides and free radical generation by the peptides

In the present study, we investigated whether or not the amyloid-beta protein (Abeta) peptide itself spontaneously generates free radicals using electron spin resonance (ESR) spectroscopy while also monitoring the aggregational state of Abeta and Abeta-induced cytotoxicity. The present results demonstrated a four-line spectrum in the presence of both Abeta40 and Abeta42 with Ntert-butyl-alpha-phenylnitrone (PBN), but not in the presence of PBN alone in phosphate-buffered saline (PBS). The fact that the four-line spectrum obtained for the Abeta/PBN in PBS was completely abolished in the presence of the iron-chelating agent Desferal demonstrated the observed four-line spectrum to be iron-dependent. The present study also revealed that either Abeta40 or Abeta42 with PBN in phosphate buffer (PB) did not produce any definite four-line spectrum. Both a thioflavine-T (Th-T) fluorometric assay and circular dichroism (CD) spectroscopy showed the amyloid fibril formation of Abeta in PBS to be much higher than that of Abeta in PB. Moreover, Abeta-induced cytotoxicity assays showed Abeta incubated in PBS to be more cytotoxic than that incubated in PB. These results thus suggest that Abeta-associated free radical generation is strongly influenced by the aggregational state of the peptides.

Inhibitory effect of voglibose and gymnemic acid on maltose absorption in vivo

AIM: To determine whether diabetic care can be improved by combination of voglibose and gymnemic acid (GA), we compared the combinative and individual effects of voglibose and GA on maltose absorption in small intestine.

METHODS: The small intestine 30 cm long from 2 cm caudal ward Treitz’s ligament of Wistar rat was used as an in situ loop, which was randomly perfused in recircular mode with maltose (10 mmol/L) with or without different dosages of voglibose and/or GA for 1 h. To compare the time course, perfusion of 10 mmol/L maltose was repeated four times. Each time continued for 1 h and separated by 30 min rinse. In the first time, lower dosages of GA (0.5 g/L) and/or voglibose (2 μmol/L) were contained except control.

RESULTS: Absorptive rate of maltose was the lowest in combinative group (P < 0.05, ANOVA), for example, the inhibition rate was about 37% during the first hour when0.5 g/L-GA and 2 μmol/L voglibose with 10 mmol/L maltose were perfused in the loop. The onset time was shortened to 30 min and the effective duration was prolonged to 4 h with the combination; therefore the total amount of maltose absorption during the effective duration was inhibited more significantly than that in the individual administration (P < 0.05, U test of Mann Whitney). The effect of GA on absorptive barriers of the intestine played an important role in the combinative effects.

CONCLUSION: There are augmented effects of voglibose and GA. The management of diabetes mellitus can be improved by employing the combination.

Inhibitory effect and mechanism of acarbose combined with gymnemic acid on maltose absorption in rat intestine

AIM: To compare the combinative and individual effect of acarbose and gymnemic acid (GA) on maltose absorption and hydrolysis in small intestine to determine whether nutrient control in diabetic care can be improved by combination of them.

METHODS: The absorption and hydrolysis of maltose were studied by cyclic perfusion of intestinal loops in situ and motility of the intestine was recorded with the intestinal ring in vitro using Wistar rats.

RESULTS: The total inhibitory rate of maltose absorption was improved by the combination of GA (0.1 g/L-1.0 g/L) and acarbose (0.1 mmol/L-2.0 mmol/L) throughout their effective duration (P < 0.05, U test of Mann-Whitney), although the improvement only could be seen at a low dosage during the first hour. With the combination, inhibitory duration of acarbose on maltose absorption was prolonged to 3 h and the inhibitory effect onset of GA was fastened to 15 min. GA suppressed the intestinal mobility with a good correlation (r = 0.98) to the inhibitory effect of GA on maltose absorption and the inhibitory effect of 2 mmol/L (high dose) acarbose on maltose hydrolysis was dual modulated by 1 g/L GA in vivo indicating that the combined effects involved the functional alteration of intestinal barriers.

CONCLUSION: There are augmented effects of acarbose and GA, which involve pre-cellular and paracellular barriers. Diabetic care can be improved by employing the combination.

Stabilization of hen egg white lysozyme by a cavity-filling mutation

Stabilization of a protein using cavity-filling strategy has hardly been successful because of unfavorable van der Waals contacts. We succeeded in stabilizing lysozymes by cavity-filling mutations. The mutations were checked by a simple energy minimization in advance. It was shown clearly that the sum of free energy change caused by the hydrophobicity and the cavity size was correlated very well with protein stability. We also considered the aromatic-aromatic interaction. It is reconfirmed that the cavity-filling mutation in a hydrophobic core is a very useful method to stabilize a protein when the mutation candidate is selected carefully.

Effective protein folding in simple random search

Here I show the following facts using a simple random search model without including any sophisticated energy term. As the size of elements exponentially affects the efficiency of folding, it can be remarkably enhanced by dividing the elements into small blocks. As the folding of the blocks is completely independent, the total folding time can be reduced to the folding time of the single hardest block. This result gives the simplest and most straightforward answer to the Levinthal paradox.

Mutant mouse lysozyme carrying a minimal T cell epitope of hen egg lysozyme evokes high autoantibody response

Self proteins including foreign T cell epitope induce autoantibodies. We evaluated the relationship between the size of foreign Ag introduced into self protein and the magnitude of autoantibody production. Mouse lysozyme (ML) was used as a model self protein, and we prepared three different ML derivatives carrying T cell epitope of hen egg white lysozyme (HEL) 107-116, i.e, heterodimer of ML and HEL (ML-HEL), chimeric lysozyme that has residue 1-82 of ML and residue 83-130 of HEL in its sequence (chiMH), and mutant ML that has triple mutations rendering the most potent T cell epitope of HEL (sequence 107-116). Immunization of BALB/c mice with these three ML derivatives induced anti-ML autoantibody responses, whereas native ML induced no detectable response. In particular, mutML generated a 10(4) times higher autoantibody titer than did ML-HEL. Anti-HEL107-116 T cell-priming activities were almost similar among the ML derivatives. The heterodimerization of mutant ML and HEL led to significant reduction of the autoantibody response, whereas the mixture did not. These results show that size of the nonself region in modified self Ag has an important role in determining the magnitude of the autoantibody response, and that decrease in the foreign region in a modified self protein may cause high-titered autoantibody response.

Relationship between local structure and stability in hen egg white lysozyme mutant with alanine substituted for glycine

We prepared five mutant lysozymes in which glycines whose dihedral angles are located in the region of the left-handed helix, Gly49, Gly67, Gly71, Gly102 and Gly117, were mutated to an alanine residue. From analyses of their thermal stabilities using differential scanning calorimetry, most of them were more destabilized than the native lysozyme, except for the G102A mutant, which has a stability similar to that of the native lysozyme at pH 2.7. As for the destabilized mutant lysozymes, their X-ray crystallographic analyses showed that their global structures did not change but that the local structures changed slightly. By examining the dihedral angles at the mutation sites based on X-ray crystallographic results, it was found that the dihedral angles at these mutation sites tended to adopt favorable values in a Ramachandran plot and that the extent and direction of their shifts from the original value had similar tendencies. Therefore, the change in dihedral angles may be the cause of the slight local structural changes around the mutation site. On the other hand, regarding the mutation of G102A, the global structure was almost identical with that of the native structure but the local structure was drastically changed. Therefore, it was suggested that the drastic local conformational change might be effective in releasing the unfavorable interaction of the native state at the mutation site.

Angiotensin-converting enzyme inhibitor inhibits dehydration-enhanced fever induced by endotoxin in rats

It has been reported that a host develops a marked fever under dehydrated conditions compared with normally hydrated conditions (11). The present study was carried out to investigate whether ANG II is involved in the enhancement seen in dehydrated rats of the fever induced by bacterial endotoxin. The results showed that intravenous injection of bacterial endotoxin produced a fever in dehydrated rats (rats deprived of water for 24 h) that was significantly greater than that seen in normally hydrated rats. In contrast, dehydration had no effect on the fever induced by intravenous interleukin-1beta (IL-1beta). Under dehydrated conditions, the enhanced endotoxin-induced fever was significantly inhibited by the angiotensin-converting enzyme inhibitor lisinopril, but the IL-1beta fever was not. These results suggest that the dehydration-induced enhancement of endotoxin fever is due, at least in part, to the action of ANG II, which elicits an increased production of pyrogenic cytokines such as IL-1.

Analysis of the internal motion of free and ligand-bound human lysozyme by use of 15N NMR relaxation measurement: a comparison with those of hen lysozyme

Human lysozyme has a structure similar to that of hen lysozyme and differs in amino acid sequence by 51 out of 129 residues with one insertion at the position between 47 and 48 in hen lysozyme. The backbone dynamics of free or (NAG)3-bound human lysozyme has been determined by measurements of 15N nuclear relaxation. The relaxation data were analyzed using the Lipari-Szabo formalism and were compared with those of hen lysozyme, which was already reported (Mine S et al.. 1999, J Mol Biol 286:1547-1565). In this paper, it was found that the backbone dynamics of free human and hen lysozymes showed very similar behavior except for some residues, indicating that the difference in amino acid sequence did not affect the behavior of entire backbone dynamics, but the folded pattern was the major determinant of the internal motion of lysozymes. On the other hand, it was also found that the number of residues in (NAG)3-bound human and hen lysozymes showed an increase or decrease in the order parameters at or near active sites on the binding of (NAG)3, indicating the increase in picosecond to nanosecond. These results suggested that the immobilization of residues upon binding (NAG)3 resulted in an entropy penalty and that this penalty was compensated by mobilizing other residues. However, compared with the internal motions between both ligand-bound human and hen lysozymes, differences in dynamic behavior between them were found at substrate binding sites, reflecting a subtle difference in the substrate-binding mode or efficiency of activity between them.

Expression and characterization of human rheumatoid factor single-chain Fv

The variable region of heavy chain [V(H)] of human rheumatoid factor (hRF) IgM was connected with the variable region of light chain [V(L)] with the peptide-linker (GGGSGGGSGGGS) by genetic engineering method and the single-chain Fv (scFv) was expressed in E. coli. On design, scFv and scFv (tag) were planned; the latter had a detection marker at the carboxyl-terminal. These scFvs were expressed as inclusion bodies in E. coli, purified in the presence of 8 M urea by gel filtration and renatured to the active form in vitro. As a control, the Fv, non-covalently associated V(H) and V(L) fragments, was also constructed. The 3 derivatives showed almost the same binding activity to rabbit-IgG to which hRF is cross-reactive. ScFv (tag) was the most stable against urea among the 3 derivatives.

Remarkable thermal stability of doubly intramolecularly cross-linked hen lysozyme

In order to examine how a protein can be effectively stabilized, two intramolecular cross-links, Glu35-Trp108 and Lys1-His15, which have few unfavorable interactions in the folded state, were simultaneously introduced into hen lysozyme. Both of the intramolecularly cross-linked lysozymes, 35-108 CL and 1-15 CL, containing cross-links Glu35-Trp108 and Lys1-His15, respectively, showed increases in thermal stability of 13.9 and 5.2 degrees C, respectively, over that of wild type, at pH 2.7. On the other hand, a doubly cross-linked lysozyme showed an increase in thermal stability of 20.8 degrees C over that of wild type, under identical conditions. Since the sum of the differences in denaturation temperature between wild type and each of the cross-linked lysozymes was nearly equal to that between wild type and the doubly cross-linked lysozyme, we suggest that the efficient stabilization of the lysozyme molecule was the direct result of the double intramolecular cross-links.

Construction of the single-chain Fv from 196-14 antibody toward ovarian cancer-associated antigen CA125

The variable regions of heavy- and light-chains of mouse monoclonal antibody 196-14 toward ovarian cancer-associated antigen CA125 were linked with a peptide linker (GSTSGSGKSSEGKG) and a histidine tag was attached at the carboxyl terminal. This single-chain Fv (scFv) with a histidine tag was expressed in Escherichia coli as an inclusion body. The inclusion body was solubilized with guanidium chloride, followed by purification on nickel nitrilotriacetic acid agarose column and refolding into the active form. The scFv thus obtained bound to the Siso cells, which express CA125, and may recognize the same epitope as the parental 196-14 antibody IgG does.

Construction of a screening system for selecting lysozyme mutants unable to form a stable structure from random mutants

To collect folding information, we screened and analyzed the recombinant hen lysozyme mutants which were not secreted from yeast. As model mutants, Leu8Arg, Ala10Gly, and Met12Arg were prepared by site-directed mutagenesis and analyzed as to whether they were secreted from yeast or not. Consequently, Ala10Gly was found to be secreted from yeast, but Leu8Arg and Met12Arg were not. Next, these mutants were expressed in Escherichia coli and refolded in vitro. As a result, Ala10Gly folded as the wild-type did. Leu8Arg efficiently refolded in renaturation buffer containing glycerol. Met12Arg did not refold even in the presence of glycerol. These results show that the Ala10Gly mutation does not affect folding or stability, that Leu8Arg is too unstable to be secreted from yeast, and that Met12Arg may be very unstable or the mutation affects the folding pathway. We screened the mutants that were not secreted by yeast from a randomly mutated lysozyme library, and obtained Asp18His/Leu25Arg and Ala42Val/Ser50Ile/Leu56Gln. These two mutants were expressed in E. coli and then refolded in the presence of urea or glycerol. These mutants were refolded only in the presence of glycerol. Each single mutant of Asp18His/Leu25Arg and Ala42Val/Ser50Ile/Leu56Gln was independently prepared and folded in vitro. The results showed that Leu25Arg and Leu56Gln were the dominant mutations, respectively, which cause destabilization. These results show that the mutant lysozymes which were not secreted from yeast may be unstable or have a defect in the folding pathway. Thus, we established a screening system for selecting mutants which are unable to form a stable structure from random mutants.

The molecular weight ratio of monomethoxypolyethylene glycol (mPEG) to protein determines the immunotolerogenicity of mPEG proteins

Immunotolerogenic activity of monomethoxypolyethylene glycol- (mPEG) conjugated proteins is a beneficial property in protein pharmaceutics. However, procedures for the preparation of tolerogenic mPEG proteins have not yet been defined. We prepared mPEG proteins with different mPEG contents using three proteins, hen egg lysozyme, ovalbumin and bovine gamma globulin, and their tolerogenicities to antigen-specific T and B cell responses were examined. We found the most appropriate ratio of tolerance induction to be 1.5-2.0, which is the molecular weight ratio of conjugated total mPEGs to protein. This value may assist in the preparation of tolerogenic mPEG proteins.

Induction of salivary gurmarin-binding proteins in rats fed gymnema-containing diets

Gymnema sylvestre, a tropical plant, contains gurmarin that selectively suppresses sucrose responses of the chorda tympani nerve in rats and mice. We investigated preference for taste solutions and saliva composition in rats fed a diet containing this plant (gymnema diet). Preference for 0.01 M sucrose and a mixture of 0.03 M sucrose and 0.03 mM quinine-HCl significantly decreased at 1-2 days after the start of the gymnema diet and subsequently returned closely to the control levels within about a week. There was no significant change in preference for NaCl, monosodium glutamate and quinine-HCl during feeding trials. Submandibular saliva of rats fed the gymnema diet for 4 and 14 days showed an inhibitory effect on immunoreaction between gurmarin and antigurmarin serum. Analyses using electrophoresis and affinity chromatography indicated that the saliva contains gurmarin binding proteins with molecular weights of 15, 16, 45, 60 and 66 kDa. These results suggest that reduction of preference for sucrose was probably caused by gurmarin contained in the gymnema diet and subsequent restoration of the preference may be due to suppression of the effect of gurmarin by salivary gurmarin-binding proteins induced by the gymnema diet.

Extended blood half-life of monomethoxypolyethylene glycol-conjugated hen lysozyme is a key parameter controlling immunological tolerogenicity

The blood half-life of a protein is prolonged by conjugating a protein with a linear amphiphilic polymer, monomethoxypolyethylene glycol (mPEG). The conjugation gives a protein immunotolerogenicity; hence, it is likely that the long half-life is crucial for the tolerogenicity. We prepared a tolerogenic mPEG conjugate of hen egg lysozyme (mPEG1.5-HEL), which is conjugated 1.5-fold the molecular weight of mPEG against that of HEL, and evaluated the relationship between in vivo stability and the tolerogenicity. mPEG1.5-HEL retained immunogenicity to prime HEL-specific T cell and antibody responses and had a long blood half-life, more than 27 times that of native HEL. The tolerant state was maintained as long as mPEG1.5-HEL was detected in sera. With a decrease in the blood mPEG1.5-HEL level, the tolerant state returned gradually to the responsive state; however, reinjection of mPEG1.5-HEL again restored the tolerance. Thus, the extended blood half-life of HEL by mPEG conjugation is probably vital for establishing and maintaining the tolerant states.

Sweet taste responses of mouse chorda tympani neurons: existence of gurmarin-sensitive and -insensitive receptor components

Inhibitory effects of gurmarin (gur) on responses to sucrose and other sweeteners of single fibers of the chorda tympani nerve in C57BL mice were examined. Of 30 single fibers that strongly responded to 0. 5 M sucrose but were not or to lesser extent responsive to 0.1 M NaCl, 0.01 M HCl, and 0.02 M quinine HCl (sucrose-best fibers), 16 fibers showed large suppression of responses to sucrose and other sweeteners by lingual treatment with 4.8 microM (approximately 20 microg/ml) gur (suppressed to 4-52% of control: gur-sensitive fibers), whereas the remaining 14 fibers showed no such gur inhibition (77-106% of control: gur-insensitive fibers). In gur-sensitive fibers, responses to sucrose inhibited by gur recovered to approximately 70% of control responses after rinsing the tongue with 15 mM beta-cyclodextrin and were almost abolished by further treatment with 2% pronase. In gur-insensitive fibers, sucrose responses were not inhibited by gur, but were largely suppressed by pronase. These results suggest existence of two different receptor components for sweeteners with different susceptibilities to gur in mouse taste cells, one gur sensitive and the other gur insensitive. Taste cells possessing each component may be specifically innervated by a particular type of chorda tympani neurons.

Inhibitory effect of gymnemic acid on intestinal absorption of oleic acid in rats

Gymnemic acid, a mixture of triterpene glycosides extracted from the leaves of Gymnema sylvestre, is known to inhibit the intestinal absorption of glucose in human and rats. This work examined the effect of gymnemic acid on oleic acid absorption by the method of intestinal perfusion in rats. The results showed the following. (i) Gymnemic acid potently inhibited the absorption of oleic acid in intestine. (ii) This inhibition was dose dependent and reversible. (iii) The extent of inhibition and the recovery progress were extremely similar to that of glucose absorption. (iv) Taurocholate did not affect the inhibitory effect of gymnemic acid on oleic acid absorption, but lowering its concentration facilitated the recovery from the inhibition. (v) The absorption of oleic acid was not affected by other glycosides such as phloridzin, stevioside, and glycyrrhizin. These new findings are important for understanding the roles of gymnemic acid in therapy of diabetes mellitus and obesity.

Analysis of a catalytic pathway via a covalent adduct of D52E hen egg white mutant lysozyme by further mutation

We previously demonstrated by X-ray crystallography and electrospray mass spectrometry that D52E mutant hen lysozyme formed a covalent enzyme-substrate adduct on reaction with N-acetylglucosamine oligomer. This observation indicates that D52E lysozyme may acquire a catalytic pathway via a covalent adduct. To explain this pathway, the formation and hydrolysis reactions of the covalent adduct were investigated. Kinetic analysis indicated that the hydrolysis step was the rate-limiting step, 60-fold slower than the formation reaction. In the formation reaction, the pH dependence was bell-shaped, which was plausibly explained by the functions of the two catalytic pKas of Glu35 and Glu52. On the other hand, the pH dependence in the hydrolysis was sigmoidal with a transition at pH 4. 5, which was identical with the experimentally determined pKa of Glu35 in the covalent adduct, indicating that Glu35 functions as a general base to hydrolyze the adduct. To improve the turnover rate of D52E lysozyme, the mutation of N46D was designed and introduced to D52E lysozyme. This mutation reduced the activation energy in the hydrolysis reaction of the covalent adduct by 1.8 kcal/mol at pH 5.0 and 40 degrees C but did not affect the formation reaction. Our data may provide a useful approach to understanding the precise mechanism of the function of natural glycosidases, which catalyze via a covalent adduct.

High-level expression of uniformly 15N-labeled hen lysozyme in Pichia pastoris and identification of the site in hen lysozyme where phosphate ion binds using NMR measurements

The non-enzymatic deamidation of Asn to Asp is known to occur in proteins and peptides and is accelerated by phosphate buffer [Tyler-Cross, R. and Schirch, V. (1991) J. Biol. Chem. 25, 22549-22556]. We attempted to identify the site in lysozyme where a phosphate ion binds by means of 1H-15N HSQC measurements of 15N-labeled lysozyme, which was successfully obtained using Pichia pastoris. As a result, we found that the phosphate ion was preferentially bound to Asn-103 in hen lysozyme. The method presented here may be useful for identifying the binding site of a protein with low molecular weight substances.

Analysis of the relationship between enzyme activity and its internal motion using nuclear magnetic resonance: 15N relaxation studies of wild-type and mutant lysozyme

A mutant lysozyme where R14 and H15 are deleted together has higher activity and a similar binding ability to an inhibitor, trimer of N-acetylglucosamine ((NAG)3), compared with wild-type lysozyme. Since this has been attributed to intrinsic protein dynamic properties, we investigated the relationship between the activity and the internal motions of proteins. Backbone dynamics of the free and the complex forms with the (NAG)3 have been studied by measurement of the 15N T1 and T2 relaxation rates and NOE determinations at 600 MHz. Analysis of the data using the model-free formalism showed that the generalized order parameters (S2) were almost the same in wild-type and mutant lysozyme in unbound state, indicating that the mutation had little effect on the global internal motions. On the other hand, in the presence of (NAG)3, although some signals located around the active site were broadened or decreased in intensity because of strong perturbation by (NAG)3, there were several residues that showed increased or decreased backbone S2 in the complexed lysozymes. A comparison of the internal motions of the wild-type and mutant complexes showed a number of distinct dynamic differences between them. In particular, many residues located at or near active-site regions (turn 1, strand 2, turn 2 and long loop), displayed greater backbone dynamics reflecting the order parameter in mutant complex relative to mutant free. Furthermore, the Rex values at the loop C-D region, which was considered to be important for enzymatic activity, significantly increased. From these results, it was suggested that variations in the dynamics of these regions may play an important role in the enzyme activity.

In vitro binding study of adaptor protein complex (AP-1) to lysosomal targeting motif (LI-motif)

Lysosomal membrane glycoproteins carry targeting information in cytoplasmic regions. Two distinct targeting motifs in these regions, GY (glycine-tyrosine) and LI (leucine-isoleucine), have been identified and characterized. Accumulating evidence suggests that the adaptor complexes (AP-1, AP-2, and AP-3) recognize this information in cytoplasmic tails of transmembrane proteins. Here we report two different in vitro analyses (affinity beads and surface plasmon resonance) which revealed specific interaction between the cytoplasmic tail of LGP85 and AP-1 but not so with AP-2. We also noted requirement of the LI motif of the LGP85 tail in binding to the AP-1 complex. Our data and others which indicated the binding of AP-3 to the LIMP II (synonym of LGP85) tail suggest that the cytoplasmic tail of LGP85 interacts with AP-1 at the trans-Golgi network (TGN) and AP-3 at late endosomes, respectively. We propose that this sequential interaction between the lysosomal targeting signal and distinct APs along its transport pathway is responsible for the critical sorting of lysosomal membrane proteins and/or the potential proofreading system of mistargeted molecules.

Resolution and characterization of tryptophyl fluorescence of hen egg-white lysozyme by quenching- and time-resolved spectroscopy

The fluorescence spectral distributions of four tryptophan residues of hen egg-white lysozyme were analyzed using time-resolved and quenching-resolved fluorescence spectroscopy. Trp62 and Trp108 gave the fluorescence maxima at 352 nm and 342 nm, respectively. The fluorescence of Trp28 and Trp111 occurred only at 300-360 nm and they were observed as an unresolved emission band with a maximum and shoulder at 320 nm and 330 nm. The fluorescence quenching and decay parameters of each tryptophan residue reconfirmed that Trp62 was fully exposed to the solvent but Trp108 was sealed in the cage of the peptide chains and furthermore showed that Trp28 and Trp111 are under the influence of the larger fluctuational motion at the hydrophobic matrix box. The fluorescence responses of each tryptophan residue to the lysozyme-ligand interaction suggested that the internal fluctuation was reduced by the binding of ligand to give a distorted conformation to the hydrophobic matrix box region.

Amino acid sequences of lysozymes newly purified from invertebrates imply wide distribution of a novel class in the lysozyme family

Lysozymes were purified from three invertebrates: a marine bivalve, a marine conch, and an earthworm. The purified lysozymes all showed a similar molecular weight of 13 kDa on SDS/PAGE. Their N-terminal sequences up to the 33rd residue determined here were apparently homologous among them; in addition, they had a homology with a partial sequence of a starfish lysozyme which had been reported before. The complete sequence of the bivalve lysozyme was determined by peptide mapping and subsequent sequence analysis. This was composed of 123 amino acids including as many as 14 cysteine residues and did not show a clear homology with the known types of lysozymes. However, the homology search of this protein on the protein or nucleic acid database revealed two homologous proteins. One of them was a gene product, CELF22 A3.6 of C. elegans, which was a functionally unknown protein. The other was an isopeptidase of a medicinal leech, named destabilase. Thus, a new type of lysozyme found in at least four species across the three classes of the invertebrates demonstrates a novel class of protein/lysozyme family in invertebrates. The bivalve lysozyme, first characterized here, showed extremely high protein stability and hen lysozyme-like enzymatic features.

High pressure NMR study of a small protein, gurmarin

The effect of pressure on the structure of gurmarin, a globular, 35-residue protein from Gymnema sylvestre, was studied in aqueous environment (95% 1H2O/5% 2H2O, pH 2.0) with an on-line variable pressure NMR system operating at 750 MHz. Two-dimensional TOCSY and NOESY spectra were measured as functions of pressure between 1 and 2000 bar at 40 degrees C. Practically all the proton signals of gurmarin underwent some shifts with pressure, showing that the entire protein structure responds to, and is altered by, pressure. Most amide protons showed different degrees of low field shifts with pressure, namely 0-0.2 ppm with an average of 0.051 ppm at 2000 bar, showing that they are involved in hydrogen bonding and that these hydrogen bonds are shortened by pressure by different degrees. The tendency was also confirmed that the chemical shifts of the amide protons exposed to the solvent (water) are more sensitive to pressure than those internally hydrogen bonded with carbonyls. The pressure-induced shifts of the H alpha signals of the residues in the beta-sheet showed a negative correlation with the 'folding' shifts (difference between the shift at 1 bar and that of a random coil), suggesting that the main-chain torsion angles of the beta-sheet are slightly altered by pressure. Significant pressure-induced shifts were also observed for the side-chain protons (but no larger than 10% of the 'folding' shifts), demonstrating that the tertiary structure of gurmarin is also affected by pressure. Finally, the linearity of the pressure-induced shifts suggest that the compressibility of gurmarin is invariant in the pressure range between 1 and 2000 bar.

Inhibitory effect of gymnemic acid on intestinal absorption of oleic acid in rats

Gymnemic acid, a mixture of triterpene glycosides extracted from the leaves of Gymnema sylvestre, is known to inhibit the intestinal absorption of glucose in human and rats. This work examined the effect of gymnemic acid on oleic acid absorption by the method of intestinal perfusion in rats. The results showed the following. (i) Gymnemic acid potently inhibited the absorption of oleic acid in intestine. (ii) This inhibition was dose dependent and reversible. (iii) The extent of inhibition and the recovery progress were extremely similar to that of glucose absorption. (iv) Taurocholate did not affect the inhibitory effect of gymnemic acid on oleic acid absorption, but lowering its concentration facilitated the recovery from the inhibition. (v) The absorption of oleic acid was not affected by other glycosides such as phloridzin, stevioside, and glycyrrhizin. These new findings are important for understanding the roles of gymnemic acid in therapy of diabetes mellitus and obesity.

Kinetic measurement of the interaction between a lysozyme and its immobilized substrate analogue by means of surface plasmon resonance

A method for evaluating the association and dissociation rate constants of interaction between a lysozyme and its substrate analogue, an immobilized p-aminophenyl-tri-N-acetyl-beta-chitotrioside, by means of surface plasmon resonance has been developed. Site-specific immobilization of p-aminophenyl-tri-N-acetyl-beta-chitotrioside, which is a product of p-nitrophenyl-tri-N-acetyl-beta-chitotrioside, on carboxymethyldextran linked to the surface of the cuvette of the instrument, IAsys, was carried out by catalysis with EDC/NHS. The kinetic parameters of the interaction between hen or human lysozyme and the immobilized substrate analogue indicated that a larger dissociation constant of the human lysozyme-immobilized substrate analogue complex depended on a smaller association rate constant. The kinetic parameters of the interaction between the immobilized substrate analogue and a mutant hen lysozyme, in which Arg14 and His15 are deleted, with higher activity than the wild type hen lysozyme were measured. It was suggested that the higher activity of the mutant lysozyme was due to faster removal of the substrate from the active site cleft and/or the formation of a stabler and better complex as to hydrolysis.

Investigation of the structural basis for thermostability of DNA-binding protein HU from Bacillus stearothermophilus

Site-directed mutagenesis was used to identify amino acid residues essential for the thermostability of the DNA-binding protein HU from the thermophile Bacillus stearothermophilus (BstHU). Two mutants, BstHU-A27S and BstHU-V42I, in which Ala27 and Val42 in BstHU were replaced by the corresponding amino acids Ser27 and Ile42, respectively, in the homologue from a mesophile B. subtilis (BsuHU), were less stable than the wild-type BstHU (63.9 degreesC), showing Tm values of 58.4 degreesC and 60.1 degreesC, respectively, as estimated by circular dichroism (CD) analysis at pH 7.0. The denaturation of two mutants was further characterized using differential scanning calorimetry; the Tm values obtained by calorimetric analysis were in good agreement with those estimated by CD analysis. The results suggest that Ala27 and Val42 are partly responsible for enhancing the thermostability of BstHU. When considered together with previous results, it is revealed that Gly15, Ala27, Glu34, Lys38, and Val42 are essential for the thermostability of thermophilic protein BstHU. Moreover, five thermostabilizing mutations were simultaneously introduced into BsuHU, which resulted in a quintuple mutant with a Tm value of 71.3 degreesC, which is higher than that of BstHU, and also resulted in insusceptibility to proteinase digestion.

Reduction of the suppressive effects of gurmarin on sweet taste responses by addition of beta-cyclodextrin

Cyclodextrins (CDs) have the remarkable ability to form inclusion complexes with a wide variety of guest molecules. In the present study, possible influences of CDs on gurmarin inhibition of the chorda tympani responses to sucrose were examined in C57BL mice. Responses to sucrose were suppressed to approximately 50% of control by treatment of the tongue with 30 micrograms/ml (approximately 7.1 microM) gurmarin. Rinsing the tongue with 15 mM beta-CD after gurmarin gave rapid recovery of the suppressed sucrose responses to approximately 85% of control, whereas 15 mM alpha- or gamma-CD did not. When gurmarin was mixed with beta-CD, the suppressive effects of gurmarin on sucrose responses were largely reduced. No such reduction was observed for mixtures with alpha- and gamma-CD. Gurmarin includes tyrosine and tryptophan residues whose aromatic rings are directed outward and can probably form inclusion complexes with beta-CD. Therefore, the observed reduction of the effects of gurmarin may be due to steric hindrances in inclusion complexes of gurmarin with beta-CD that may interfere with gurmarin binding to sweet taste receptors.