Recombinant Multi-l-Arginyl-Poly-l-Aspartate (Cyanophycin) as an Emerging Biomaterial

Multi-l-arginyl-poly-l-aspartate (MAPA) is a non-ribosomal polypeptide which synthesis is directed by cyanophycin synthetase, and its production can be achieved using recombinant microorganisms carrying the cphA gene. Along its poly-aspartate backbone, arginine or lysine links to each aspartate via an isopeptide bond. MAPA is a zwitterionic polyelectrolyte full of charged carboxylic, amine, and guanidino groups. In aqueous solution, MAPA exhibits dual thermal and pH responses similar to those stimuli-responsive polymers. Being biocompatible, the films containing MAPA can support cell proliferation and elicits minimal immune response in macrophages. Dipeptides from MAPA after enzymatic treatments can provide nutritional benefits. In light of the increasing interest in MAPA, this article focuses on the recent discovery of the function of cyanophycin synthetase and the potentials of MAPA as a biomaterial.

Altering the substrate specificity of recombinant l-rhamnose isomerase from Thermoanaerobacterium saccharolyticum NTOU1 to favor d-allose production

l-Rhamnose isomerase (l-RhI) catalyzes rare sugar isomerization between aldoses and ketoses. In an attempt to alter the substrate specificity of Thermoanaerobacterium saccharolyticus NTOU1 l-RhI (TsRhI), residue Ile102 was changed to other polar or charged amino acid residues by site-directed mutagenesis. The results of activity-screening using different substrates indicate that I102N, I102Q, and I102R TsRhIs can increase the preference against d-allose in comparison with the wild-type enzyme. The catalytic efficiencies of the purified I102N, I102Q, and I102R TsRhIs against d-allose are 148 %, 277 %, and 191 %, respectively, of that of wild-type enzyme, while those against l-rhamnose are 100 %, 167 % and 87 %, respectively. Mutant I102N, I102Q, and I102R TsRhIs were noted to have the altered substrate specificity, and I102Q TsRhI has the highest catalytic efficiency against d-allose presumably through the formation of an additional hydrogen bond with d-allose. The purified wild-type and mutant TsRhIs were further used to produce d-allose from 100 g/L d-fructose in the presence of d-allulose 3-epimerase, and the yields can reach as high as 22 % d-allulose and 12 % d-allose upon equilibrium. I102Q TsRhI takes only around half of the time to reach the same 12 % d-allose yield, suggesting that this mutant enzyme has a potential to be applied in d-allose production.

Reversible Self-Assembly Nanovesicle of UCST Response Prepared with Multi-l-arginyl-poly-l-aspartate Conjugated with Polyethylene Glycol

Multi-L-arginyl-poly-L-aspartate (MAPA), also known as cyanophycin, containing a backbone of polyaspartate with arginine and lysine as side chains, was prepared with recombinant Escherichia coli. The insoluble part (iMAPA) was conjugated with polyethylene glycol (PEG) at two different levels, high (iMAPA(PEG)h) and low (iMAPA(PEG)l). Both levels of conjugation exhibited UCST (upper critical solution temperature)-type responses in the pH range of 3-10 at a concentration of 2 mg/mL. The cloud-point temperature of each conjugate also showed a positive correlation with concentration in PBS, falling between 20 to 58 °C at a concentration from 0.1 to 3 mg/mL. Hysteresis was observed to follow approximate paths under the same condition during repeated heating and cooling. Notably, the reversible formation of core-shell vesicles appeared at room temperature in PBS with a size of around 25 to 60 nm, as measured by DLS and observed under TEM. The reversibility was further employed to encapsulate doxorubicin (Dox) at different weight ratios of Dox to iMAPA(PEG)h. An encapsulation efficiency could reach as high as 70% with an equivalent loading capacity of 1.5 mg Dox/mg iMAPA(PEG)h. The Dox-loaded vesicles stayed stable at 4 °C for up to 4 weeks, with a minimal leakage below 2% and a slightly dilated morphology. Temperature-triggered release of Dox from the vesicles could be achieved by a step change of 5 °C successively from 37 to 62 °C in an effort to induce an initial 10% release at 37 °C gradually to complete release at 62 °C.

Characterization of a recombinant d-allulose 3-epimerase from Agrobacterium sp. ATCC 31749 and identification of an important interfacial residue

d-Allulose 3-epimerase (DAEase) catalyzes the epimerization between d-fructose and d-allulose. We had PCR-cloned and overexpressed the gene encoding Agrobacterium sp. ATCC 31749 DAEase (AsDAEase) in Escherichia coli. A high yield of active AsDAEase, 35,300U/L or 1350U/g of wet cells, was acquired with isopropyl β-d-1-thiogalactopyranoside induction at 20°C for 20h. Although only six residues including residue 234 located in tetrameric interface are different between AsDAEase and A. tumefaciens DAEase (AtDAEase), the specific activity of purified AsDAEase is much larger than that of AtDAEase. The optimal pHs and optimal temperatures of the purified recombinant AsDAEase are 7.5-8.0 and 55-60°C, respectively. The half-life of the enzyme is 267min at 55°C in the presence of 0.1mM Co²⁺, and the equilibrium ratio between d-allulose and d-fructose is 30:70 at 55°C. Besides characterizing AsDAEase, mutation N234D was constructed to assess its influence on activity. The specific activity of the purified N234D AsDAEase is only 25.5% of wild-type's activity, suggesting residue N234 is an important interfacial residue which substantially affects enzyme activity. The high specific activity and high expression yield of AsDAEase suggest its prospect to be applied in d-allulose production.

Identification of substrate-binding and selectivity-related residues of maltooligosyltrehalose synthase from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

Maltooligosyltrehalose synthase (MTSase) is a key enzyme in the synthesis of trehalose. Computer simulations using AutoDock and NAMD were employed to assess the substrate-binding and selectivity-related residues of MTSase. We introduced mutations at residues D411, D610, and R614 to determine the substrate-binding residues of Sulfolobus solfataricus ATCC 35092 MTSase, and introduced mutations at residues P402, A406, and V426 to investigate the enzyme's selectivity-related residues. Kinetic studies of D411A, D610A, and R614A MTSases reveal significant reductions in catalytic efficiency and cause increase in the transition-state energy of mutant MTSases, indicating that residues D411, D610, and R614 form hydrogen bonds to the substrate. Compared with wild-type MTSase, the hydrolysis: transglycosylation selectivity ratio was significantly decreased for P402Q and significantly increased for A406S MTSases, while the ratio for V426T MTSase showed little change. The results suggest that P402 and A406 residues are selectivity-related.

Interaction between trehalose and MTHase from Sulfolobus solfataricus studied by theoretical computation and site-directed mutagenesis

Maltooligosyltrehalose trehalohydrolase (MTHase) catalyzes the release of trehalose by cleaving the α-1,4-glucosidic linkage next to the α-1,1-linked terminal disaccharide of maltooligosyltrehalose. Computer simulation using the hydrogen bond analysis, free energy decomposition, and computational alanine scanning were employed to investigate the interaction between maltooligosyltrehalose and the enzyme. The same residues that were chosen for theoretical investigation were also studied by site-directed mutagenesis and enzyme kinetic analysis. The importance of residues determined either experimentally or computed theoretically were in good accord with each other. It was found that residues Y155, D156, and W218 of subsites -2 and -3 of the enzyme might play an important role in interacting with the ligand. The theoretically constructed structure of the enzyme-ligand complex was further validated through an ab initio quantum chemical calculation using the Gaussian09 package. The activation energy computed from this latter study was very similar to those reported in literatures for the same type of hydrolysis reactions.

Characterization of a thermophilic L-rhamnose isomerase from Caldicellulosiruptor saccharolyticus ATCC 43494

L-Rhamnose isomerase (EC 5.3.1.14, l-RhI) catalyzes the reversible aldose-ketose isomerization between L-rhamnose and L-rhamnulose. In this study, the L-rhi gene encoding L-RhI was PCR-cloned from Caldicellulosiruptor saccharolyticus ATCC 43494 and then expressed in Escherichia coli. A high yield of active L-RhI, 3010 U/g of wet cells, was obtained after 20 °C induction for 20 h. The enzyme was purified sequentially using heat treatment, nucleic acid precipitation, and ion-exchange chromatography. The purified L-RhI showed an apparent optimal pH of 7 and an optimal temperature at 90 °C. The enzyme was stable at pH values ranging from 4 to 11 and retained >90% activity after a 6 h incubation at 80 °C and pH 7-8. Compared with other previously characterized L-RhIs, the L-RhI from C. saccharolyticus ATCC 43494 has a good thermostability, the widest pH-stable range, and the highest catalytic efficiencies (k(cat)/K(M)) against L-rhamnose, L-lyxose, L-mannose, D-allose, and D-ribose, suggesting that this enzyme has the potential to be applied in rare sugar production.

Characterization of a thermophilic L-rhamnose isomerase from Thermoanaerobacterium saccharolyticum NTOU1

L-rhamnose isomerase (EC 5.3.1.14, L-RhI) catalyzes the reversible aldose-ketose isomerization between L-rhamnose and L-rhamnulose. In this study, the L-Rhi gene encoding L-Rhi was PCR-cloned from Thermoanaerobacterium saccharolyticum NTOU1 and then expressed in Escherichia coli. A high yield of the active L-RhI, 9780 U/g of wet cells, was obtained in the presence of 0.2 mM IPTG induction. L-RhI was purified sequentially using heat treatment, nucleic acid precipitation, and anion-exchange chromatography. The purified L-RhI showed an apparent optimal pH of 7 and an optimal temperature at 75 °C. The enzyme was stable at pH values ranging from 5 to 9, and the activity was fully retained after a 2 h incubation at 40-70 °C. L-RhI from T. saccharolyticum NTOU1 is the most thermostable L-RhI to date, and it has a high specific activity (163 U/mg) and an acceptable purity after heat treatment, suggesting that this enzyme has the potential to be used in rare sugar production.

Identification of the essential catalytic residues and selectivity-related residues of maltooligosyltrehalose trehalohydrolase from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

Maltooligosyltrehalose trehalohydrolase (MTHase) catalyzes the release of trehalose by cleaving the alpha-1,4-glucosidic linkage next to the alpha-1,1-linked terminal disaccharide of maltooligosyltrehalose. Mutations at residues D255, E286, and D380 were constructed to identify the essential catalytic residues of MTHase, while mutations at residues W218, A259, Y328, F355, and R356 were constructed to identify selectivity-related residues of the enzyme. The specific activities of the purified D255A, E286A, and D380A MTHases were only 0.15, 0.09 and 0.01%, respectively, of that of wild-type MTHase, suggesting that these three residues are essential catalytic residues. Compared with wild-type MTHase, A259S, Y328F, F355Y, and R356K MTHases had increased selectivity ratios, which were defined as the ratios of the catalytic efficiencies for glucose formation to those for trehalose formation in the hydrolysis of maltooligosaccharides and maltooligosyltrehaloses, respectively, while W218A and W218F MTHases had decreased selectivity ratios. When starch digestion was carried out at 75 degrees C and wild-type and mutant MTHases were, respectively, used with isoamylase and maltooligosyltrehalose synthase (MTSase), the ratios of initial rates of glucose formation to those of trehalose formation were inversely correlated to the peak trehalose yields.

Using disaccharides to enhance in vitro and in vivo transgene expression mediated by a lipid-based gene delivery system

BACKGROUND

Lipid-based vectors have been widely applied to in vivo and in vitro gene delivery. Disaccharides can effectively stabilize lipid membranes. This study examined whether disaccharides could enhance the transgene expression mediated by lipid-based vectors.

METHODS

Different disaccharides were incorporated into the vectors prepared with DOTAP/protamine/DNA (LPD) or with DNA/cationic liposomes containing DOTAP, DOTAP/Chol, DOTAP/DOPE, or DC-Chol/DOPE. The levels of transgene expression and internalized plasmid of CHO cells were represented by the percentages of GFP-positive cells and the fluorescence intensity of ethidium-monoazide covalently labeled plasmid, respectively. The vectors containing either cellobiose or trehalose were also intravenously injected into mouse tail vein to investigate the potentials of in vivo applications.

RESULTS

For enhancing the transgene expression, cellobiose was found to be effective for all the vectors whereas maltose decreased the effectiveness of DOTAP/Chol liposomes and LPD. For the internalization of plasmid, most disaccharides were able to increase the cellular delivery of DOTAP, DOTAP/Chol, and DOTAP/DOPE liposomes, but caused decreases in the cellular entry of DC-Chol/DOPE liposomes. An approximately linear correlation between the internalized plasmid and the transgene expression was observed for all the treatments in this study. When the vectors were administered to mouse by intravenous injection, 10-fold and 3-fold increases in the luciferase expression of lung were observed for DOTAP liposomes containing 330 mM cellobiose and trehalose, respectively.

CONCLUSIONS

This study showed that using trehalose and cellobiose with a lipid-based delivery system provides a straightforward approach to effectively enhance both in vitro and in vivo transgene expression.

Trehalose enhances transgene expression mediated by DNA-PEI complexes

Using enhancers to improve the transfection efficiency of polyethylenimine (PEI) can circumvent the needs of chemical modifications as well as subsequent purification and characterization of the modified PEI. In this study, we found that incorporating trehalose into the transfection reagent could improve the transgene expression mediated by DNA-PEI complexes. Such enhancements were not observed when trehalose was replaced by other disaccharides. In an effort to explore the mechanisms, we examined how the timing of trehalose treatments and the durations of trehalose affected the percentages of cells expressing green fluorescent protein and the levels of intracellular ethidium monoazide labeled plasmid. Treatments with trehalose for 5-120 min prior to transfection could cause drops in transfection efficiency by 30-50%; such treatments, however, hardly affected the amounts of intracellular plasmid, indicating that the preexistence of intracellular trehalose could reduce transfection efficiency without lowering the endocytic activity. The transfection efficiency remained almost unchanged when the transfected cells were treated with trehalose after the removal of transfection reagents, indicating that trehalose had minimal effects on the machinery of protein synthesis. Despite the enhanced transgene expression, the presence of trehalose during transfection showed inhibitory effects on the internalization of DNA-PEI complexes. Additionally, the extent of enhancement in transgene expression strongly depended on the duration of trehalose. As the above observations suggested, only during the transfection process when complexes and trehalose coexisted, trehalose became an effective enhancer of transgene expression mediated by DNA-PEI complexes possibly by affecting the mechanisms of intracellular trafficking.

Protein engineering of Sulfolobus solfataricus maltooligosyltrehalose synthase to alter its selectivity

Maltooligosyltrehalose synthase (MTSase) is one of the key enzymes involved in trehalose production from starch and catalyzes an intramolecular transglycosylation reaction by converting the alpha-1,4- to alpha,alpha-1,1-glucosidic linkage. Mutations at residues F206, F207, and F405 were constructed to change the selectivity of the enzyme because the changes in selectivity could reduce the side hydrolysis reaction of releasing glucose and thus increase trehalose production from starch. As compared with wild-type MTSase, F405Y and F405M MTSases had decreased ratios of the initial rate of glucose formation to that of trehalose formation in starch digestion at 75 degrees C when wild-type and mutant MTSases were, respectively, used with isoamylase and maltooligosyltrehalose trehalohydrolase (MTHase). The highest trehalose yield from starch digestion was by the mutant MTSase having the lowest initial rate of glucose formation to trehalose formation, and this predicted high trehalose yield better than the ratio of catalytic efficiency for hydrolysis to that for transglycosylation.

Expression, purification, and characterization of the maltooligosyltrehalose trehalohydrolase from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

The maltooligosyltrehalose trehalohydrolase (MTHase) mainly cleaves the alpha-1,4-glucosidic linkage next to the alpha-1,1-linked terminal disaccharide of maltooligosyltrehalose to produce trehalose and the maltooligosaccharide with lower molecular mass. In this study, the treZ gene encoding MTHase was PCR-cloned from Sulfolobus solfataricus ATCC 35092 and then expressed in Escherichia coli. A high yield of the active wild-type MTHase, 13300 units/g of wet cells, was obtained in the absence of IPTG induction. Wild-type MTHase was purified sequentially using heat treatment, nucleic acid precipitation, and ion-exchange chromatography. The purified wild-type MTHase showed an apparent optimal pH of 5 and an optimal temperature at 85 degrees C. The enzyme was stable at pH values ranging from 3.5 to 11, and the activity was fully retained after a 2-h incubation at 45-85 degrees C. The k(cat) values of the enzyme for hydrolysis of maltooligosyltrehaloses with degree of polymerization (DP) 4-7 were 193, 1030, 1190, and 1230 s(-1), respectively, whereas the k(cat) values for glucose formation during hydrolysis of DP 4-7 maltooligosaccharides were 5.49, 17.7, 18.2, and 6.01 s(-1), respectively. The K(M) values of the enzyme for hydrolysis of DP 4-7 maltooligosyltrehaloses and those for maltooligosaccharides are similar at the same corresponding DPs. These results suggest that this MTHase could be used to produce trehalose at high temperatures.

Mutations on aromatic residues of the active site to alter selectivity of the Sulfolobus solfataricus maltooligosyltrehalose synthase

Mutations Y290F, Y367F, F405Y, and Y409F located near subsite +1 were constructed in maltooligosyltrehalose synthase (MTSase) to alter the selectivity of the enzyme. These mutations were designed to evaluate the effects of hydrophobic interactions and/or hydrogen bondings on transglycosylation and side hydrolysis reactions. The catalytic efficiencies of Y290F MTSase for hydrolysis and transglycosylation reactions were only 6.6 and 5.6%, respectively, of those of wildtype MTSase, whereas the catalytic efficiencies of Y367F MTSase were decreased by about half. F405Y MTSase had similar catalytic efficiencies for transglycosylation and a somewhat lower catalytic efficiency for hydrolysis. Y409F MTSase had somewhat lower catalytic efficiencies for the transglycosylation and a similar catalytic efficiency for hydrolysis. Y290F and Y367F MTSases had large changes in delta(deltaG), suggesting that there are hydrogen bonds between the substrate and residues Y290 and Y367 of wild-type MTSase. Compared with wild-type MTSase, F405Y MTSase had decreased ratios of hydrolysis to transglycosylation, whereas Y290F, Y367F, and Y409F MTSases had increased ratios. These results suggest that use of F405Y MTSase might result in a higher yield of trehalose production from starch when it replaces wild-type MTSase.

Dependence of Transgene Expression and the Relative Buffering Capacity of Dextran-Grafted Polyethylenimine

Branched polyethylenimine (PEI) is a cationic polymer capable of forming self-assembly complexes with DNA to become a highly efficient agent used in gene delivery. Conjugation through the primary amines of PEI is a most commonly used approach further to enable the targeting delivery or to improve the stability of the DNA-polymer complexes. An understanding of how the conjugation affects the transfection mechanisms can help in the design of efficient polycationic vectors. In order to investigate the effects of conjugation, folate and the dextrans of molecular weight 1500 (dex-1500) and 10 000 (dex-10000) were used to prepare three different types of PEI conjugates: dextran-PEI, folate-PEI, and folate-dextran-PEI, which were subsequently employed to form complexes with DNA. These conjugates were found to cause less cytotoxicity than the unmodified PEI as revealed by the MTT method, and to be able to deliver an approximate amount of ethidium monoazide labeled plasmid into the cells. The efficiencies of green fluorescent protein (GFP) expression mediated by these conjugates, however, were less efficient than those mediated by the unmodified PEI. A titration experiment suggested that conjugation through the primary amines of PEI resulted in the loss of relative buffering capacity, a major factor aiding the release of plasmid from the endosomes, presumably because the conjugated molecules hindered the protonation of the PEI conjugates. When a quantitative relationship between relative buffering capacity and transfection efficiency was examined, a threshold of relative buffering capacity, around 50% of the unmodified PEI, was noted to be required for minimal detection of GFP positive cells. In addition, the cytotoxicity could be also related to the relative buffering capacity in an approximately linear trend. It is thus concluded that the severe loss of relative buffering capacity by conjugation might be attributed to the inefficiency of transgene expression mediated by the dextran-PEI conjugates.

The role of dextran conjugation in transfection mediated by dextran-grafted polyethylenimine

BACKGROUND

Conjugation through primary amines is one of the most commonly used methods to modify polycationic vectors for gene delivery. A better understanding of the effect of the conjugation on the mechanisms of transgene expression can help design efficient polycationic vectors.

METHODS

Dextran with a molecular weight of 1500 was grafted onto polyethylenimine (PEI) to produce various degrees of grafting in an effort to investigate how the conjugation affected the mechanisms of transgene expression. Flow cytometry was employed to quantitate the cellular entry of plasmid and the level of transgene expression, which were measured using ethidium monoazide labeled plasmid and green fluorescent protein (GFP), respectively. The buffering capacity of the grafted PEI was determined by titration, and the integrity of the DNA-polymer complexes were examined by exposure to heparin.

RESULTS

Grafting of dextran onto PEI was found to significantly diminish the cytotoxicity, buffering capacity, cellular entry, and the integrity of the DNA-polymer complexes. The reductions enlarged as the degree of grafting increased from 0 to 1.84%; however, at an optimal degree of grafting, the dextran-grafted PEI enhanced the percentages of GFP-positive cells to a level 3 times and 1.3 times of those mediated by unmodified PEI for CHO and MDA-MB-231 cells, respectively.

CONCLUSIONS

These results demonstrated that the conjugation of dextran onto the primary amines of PEI inhibited the entry of plasmid across the cell membrane, but the change in the structures of the DNA-polymer complexes was able to promote transgene expression when the degrees of conjugation fell below 0.64%.

Characterization of the trehalosyl dextrin-forming enzyme from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

The trehalosyl dextrin-forming enzyme (TDFE) mainly catalyzes an intramolecular transglycosyl reaction to form trehalosyl dextrins from dextrins by converting the alpha-1,4-glucosidic linkage at the reducing end to an alpha-1,1-glucosidic linkage. In this study, the treY gene encoding TDFE was PCR cloned from the genomic DNA of Sulfolobus solfataricus ATCC 35092 to an expression vector with a T7 lac promoter and then expressed in Escherichia coli. The recombinant TDFE was purified sequentially by using heat treatment, ultrafiltration, and gel filtration. The obtained recombinant TDFE showed an apparent optimal pH of 5 and an optimal temperature of 75 degrees C. The enzyme was stable in a pH range of 4.5-11, and the activity remained unchanged after a 2-h incubation at 80 degrees C. The transglycosylation activity of TDFE was higher when using maltoheptaose as substrate than maltooligosaccharides with a low degree of polymerization (DP). However, the hydrolysis activity of TDFE became stronger when low DP maltooligosaccharides, such as maltotriose, were used as substrate. The ratios of hydrolysis activity to transglycosylation activity were in the range of 0.2-14% and increased when the DP of substrate decreased. The recombinant TDFE was found to exhibit different substrate specificity, such as its preferred substrates for the transglycosylation reaction and the ratio of hydrolysis to transglycosylation of the enzyme reacting with maltotriose, when compared with other natural or recombinant TDFEs from Sulfolobus.

Starch-binding domain shuffling in Aspergillus niger glucoamylase

Aspergillus niger glucoamylase (GA) consists mainly of two forms, GAI [from the N-terminus, catalytic domain + linker + starch-binding domain (SBD)] and GAII (catalytic domain + linker). These domains were shuffled to make RGAI (SBD + linker + catalytic domain), RGAIDeltaL (SBD + catalytic domain) and RGAII (linker + catalytic domain), with domains defined by function rather than by tertiary structure. In addition, Paenibacillus macerans cyclomaltodextrin glucanotransferase SBD replaced the closely related A.niger GA SBD to give GAE. Soluble starch hydrolysis rates decreased as RGAII approximately GAII approximately GAI > RGAIDeltaL approximately RGAI approximately GAE. Insoluble starch hydrolysis rates were GAI > RGAIDeltaL > RGAI >> GAE approximately RGAII > GAII, while insoluble starch-binding capacities were GAI > RGAI > RGAIDeltaL > RGAII > GAII > GAE. These results indicate that: (i) moving the SBD to the N-terminus or replacing the native SBD somewhat affects soluble starch hydrolysis; (ii) SBD location significantly affects insoluble starch binding and hydrolysis; (iii) insoluble starch hydrolysis is imperfectly correlated with its binding by the SBD; and (iv) placing the P.macerans cyclomaltodextrin glucanotransferase SBD at the end of a linker, instead of closely associated with the rest of the enzyme, severely reduces its ability to bind and hydrolyze insoluble starch.

An additional H-bond in the alpha 1 beta 2 interface as the structural basis for the low oxygen affinity and high cooperativity of a novel recombinant hemoglobin (beta L105W)

Site-directed mutagenesis has been used to construct three recombinant mutant hemoglobins (rHbs), rHb(beta L105W), rHb(alpha D94A/betaL105W), and rHb(alpha D94A). rHb(beta L105W) is designed to form a new hydrogen bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface to lower the oxygen binding affinity by stabilizing the deoxy quaternary structure. We have found that rHb(beta L105W) does indeed possess a very low oxygen affinity and maintains normal cooperativity (P(50) = 28.2 mmHg, n(max) = 2.6 in 0.1 M sodium phosphate at pH 7.4) compared to those of Hb A (P(50) = 9.9 mmHg, n(max) = 3.2 at pH 7.4). rHb(alpha D94A/beta L105W) and rHb(alpha D94A) are expressed to provide evidence that rHb(betaL 105W) does form a new H-bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface of the deoxy quaternary structure. Our multinuclear, multidimensional nuclear magnetic resonance (NMR) studies on (15)N-labeled rHb(beta L105W) have identified the indole nitrogen-attached (1)H resonance of beta 105Trp for rHb(beta L105W). (1)H NMR studies on Hb A and mutant rHbs have been used to investigate the structural basis for the low O(2) affinity of rHb(beta L105W). Our NMR results provide evidence that rHb(beta L105W) forms a new H-bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface of the deoxy quaternary structure. The NMR results also show that these three rHbs can switch from the R quaternary structure to the T quaternary structure in their ligated state upon addition of an allosteric effector, inositol hexaphosphate. We propose that the low O(2) affinity of rHb(beta L105W) is due to the formation of a new H-bond between alpha 105Trp and alpha 94Asp in the deoxy quaternary structure.

Novel recombinant hemoglobin, rHb (beta N108Q), with low oxygen affinity, high cooperativity, and stability against autoxidation

Using our Escherichia coli expression system, we have constructed rHb (beta N108Q), a new recombinant hemoglobin (rHb), with the amino acid substitution located in the alpha(1)beta(1) subunit interface and in the central cavity of the Hb molecule. rHb (beta N108Q) exhibits low oxygen affinity, high cooperativity, enhanced Bohr effect, and slower rate of autoxidation of the heme iron atoms from the Fe(2+) to the Fe(3+) state than other low-oxygen-affinity rHbs developed in our laboratory, e.g., rHb (alpha V96W) and rHb (alpha V96W, beta N108K). It has been reported by Olson and co-workers [Carver et al. (1992) J. Biol. Chem. 267, 14443-14450; Brantley et al. (1993) J. Biol. Chem. 268, 6995-7010] that the substitution of phenylalanine for leucine at position 29 of myoglobin can inhibit autoxidation in myoglobin and at position 29 of the alpha-chain of hemoglobin can lower NO reaction in both the deoxy and the oxy forms of human normal adult hemoglobin. Hence, we have further introduced this mutation, alpha L29F, into beta N108Q. rHb (alpha L29F, beta N108Q) is stabilized against auto- and NO-induced oxidation as compared to rHb (beta N108Q), but exhibits lower oxygen affinity at pH below 7.4 and good cooperativity as compared to Hb A. Proton nuclear magnetic resonance (NMR) studies show that rHb (beta N108Q) has similar tertiary structure around the heme pockets and quaternary structure in the alpha(1)beta(1) and alpha(1)beta(2) subunit interfaces as compared to those of Hb A. The tertiary structure of rHb (alpha L29F, beta N108Q) as measured by (1)H NMR, especially the alpha-chain heme pocket region (both proximal and distal histidyl residues), is different from that of CO- and deoxy-Hb A, due to the amino acid substitution at alpha L29F. (1)H NMR studies also demonstrate that rHb (beta N108Q) can switch from the R quaternary structure to the T quaternary structure without changing ligation state upon adding an allosteric effector, inositol hexaphosphate, and reducing the temperature. On the basis of its low oxygen affinity, high cooperativity, and stability against autoxidation, rHb (beta N108Q) is considered a potential candidate for the Hb-based oxygen carrier in a blood substitute system.

Islet cell antibodies in Sulawesi macaques

Older monkeys of the Sulawesian species Macaca nigra spontaneously develop a lesion in the pancreatic islets of Langerhans in which there is deposition of amyloid and gradual degeneration of all cells, which can lead eventually to development of diabetes mellitus. Islet cell antibodies (ICA), formed in response to the release of cellular antigens, can be used to detect the islet lesion and to monitor the progression of each monkey toward diabetes. Numerous M. nigra and one M. tonkeana in captivity have been tested, but it is unknown whether the islet lesion occurs in monkeys in their natural habitat of Sulawesi. Blood samples collected from M. maurus, M. tonkeana, and hybrid M. maurus/tonkeana were assayed for ICA. When all monkeys were considered together, 33% had ICA positive against beta cells and 14% had ICA positive against alpha and/or D cells. Appearance of ICA in blood of males was virtually the same as in females. These results are similar to those found in M. nigra examined in captivity. Since all Sulawesian species share a common genetic heritage, these results would support the appearance of this lesion in their natural habitat. Cause(s) for formation of the lesion and eventual development of diabetes are unknown. There may be genetic factors or genetic predisposition to environmental factors. If environmental factors are responsible, then they must be present not only in the wild, but either carried with the monkeys or universally available, since M. nigra born in captivity also develop the lesion and diabetes after physical maturity at ca. 7+ years.

Chain-selective isotopic labeling for NMR studies of large multimeric proteins: application to hemoglobin

Multidimensional, multinuclear NMR has the potential to elucidate the mechanisms of allostery and cooperativity in multimeric proteins under near-physiological conditions. However, NMR studies of proteins made up of non-equivalent subunits face the problem of severe resonance overlap, which can prevent the unambiguous assignment of resonances, a necessary step in interpreting the spectra. We report the application of a chain-selective labeling technique, in which one type of subunit is labeled at a time, to carbonmonoxy-hemoglobin A (HbCO A). This labeling method can be used to extend previous resonance assignments of key amino acid residues, which are important to the physiological function of hemoglobin. Among these amino acid residues are the surface histidyls, which account for the majority of the Bohr effect. In the present work, we report the results of two-dimensional heteronuclear multiple quantum coherence (HMQC) experiments performed on recombinant (15)N-labeled HbCO A. In addition to the C2-proton (H epsilon(1)) chemical shifts, these spectra also reveal the corresponding C4-proton (H delta(2)) resonances, correlated with the N epsilon(2) and N delta(1) chemical shifts of all 13 surface histidines per alpha beta dimer. The HMQC spectrum also allows the assignment of the H delta(1), H epsilon(1), and N epsilon(1) resonances of all three tryptophan residues per alpha beta dimer in HbCO A. These results indicate that heteronuclear NMR, used with chain-selective isotopic labeling, can provide resonance assignments of key regions in large, multimeric proteins, suggesting an approach to elucidating the solution structure of hemoglobin, a protein with molecular weight 64.5 kDa.

Assessment of roles of surface histidyl residues in the molecular basis of the Bohr effect and of beta 143 histidine in the binding of 2,3-bisphosphoglycerate in human normal adult hemoglobin

Site-directed mutagenesis has been used to construct two mutant recombinant hemoglobins (rHbs), rHb(betaH116Q) and rHb(betaH143S). Purified rHbs were used to assign the C2 proton resonances of beta116His and beta143His and to resolve the ambiguous assignments made over the past years. In the present work, we have identified the C2 proton resonances of two surface histidyl residues of the beta chain, beta116His and beta143His, in both the carbonmonoxy and deoxy forms, by comparing the proton nuclear magnetic resonance (NMR) spectra of human normal adult hemoglobin (Hb A) with those of rHbs. Current assignments plus other previous assignments complete the assignments for all 24 surface histidyl residues of human normal adult hemoglobin. The individual pK values of 24 histidyl residues of Hb A were also measured in deuterium oxide (D(2)O) in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) buffer in the presence of 0.1 M chloride at 29 degrees C by monitoring the shifts of the C2 proton resonances of the histidyl residues as a function of pH. Among those surface histidyl residues, beta146His has the biggest contribution to the alkaline Bohr effect (63% at pH 7.4), and beta143His has the biggest contribution to the acid Bohr effect (71% at pH 5.1). alpha20His, alpha112His, and beta117His have essentially no contribution; alpha50His, alpha72His, alpha89His, beta97His, and beta116His have moderate positive contributions; and beta2His and beta77His have a moderate negative contribution to the Bohr effect. The sum of the contributions from 24 surface histidyl residues accounted for 86% of the alkaline Bohr effect at pH 7.4 and about 55% of the acid Bohr effect at pH 5.1. Although beta143His is located in the binding site for 2,3-bisphosphoglycerate (2,3-BPG) according to the crystal structure of deoxy-Hb A complexed with 2, 3-BPG, beta143His is not essential for the binding of 2,3-BPG in the neutral pH range according to the proton NMR and oxygen affinity studies presented here. With the accurately measured and assigned individual pK values for all surface histidyl residues, it is now possible to evaluate the Bohr effect microscopically for novel recombinant Hbs with important functional properties, such as low oxygen affinity and high cooperativity. The present study further confirms the importance of a global electrostatic network in regulating the Bohr effect of the hemoglobin molecule.

Identification of a phosphate regulatory site and a low affinity binding site for glucose 6-phosphate in the N-terminal half of human brain hexokinase

Crystal structures of human hexokinase I reveal identical binding sites for phosphate and the 6-phosphoryl group of glucose 6-phosphate in proximity to Gly87, Ser88, Thr232, and Ser415, a binding site for the pyranose moiety of glucose 6-phosphate in proximity to Asp84, Asp413, and Ser449, and a single salt link involving Arg801 between the N- and C-terminal halves. Purified wild-type and mutant enzymes (Asp84 --> Ala, Gly87 --> Tyr, Ser88 --> Ala, Thr232 --> Ala, Asp413 --> Ala, Ser415 --> Ala, Ser449 --> Ala, and Arg801 --> Ala) were studied by kinetics and circular dichroism spectroscopy. All eight mutant hexokinases have kcat and Km values for substrates similar to those of wild-type hexokinase I. Inhibition of wild-type enzyme by 1,5-anhydroglucitol 6-phosphate is consistent with a high affinity binding site (Ki = 50 microM) and a second, low affinity binding site (Kii = 0.7 mM). The mutations of Asp84, Gly87, and Thr232 listed above eliminate inhibition because of the low affinity site, but none of the eight mutations influence Ki of the high affinity site. Relief of 1,5-anhydroglucitol 6-phosphate inhibition by phosphate for Asp84 --> Ala, Ser88 --> Ala, Ser415 --> Ala, Ser449 --> Ala and Arg801 --> Ala mutant enzymes is substantially less than that of wild-type hexokinase and completely absent in the Gly87 --> Tyr and Thr232 --> Ala mutants. The results support several conclusions. (i) The phosphate regulatory site is at the N-terminal domain as identified in crystal structures. (ii) The glucose 6-phosphate binding site at the N-terminal domain is a low affinity site and not the high affinity site associated with potent product inhibition. (iii) Arg801 participates in the regulatory mechanism of hexokinase I.

The effects of methylphenidate and maturation on exploratory activity in rats

Treatment of attention-deficit hyperactivity disorder with stimulants such as methylphenidate reduces motor activity and improves performance of tasks requiring attention, learning, and memory. The present study reports the patterns of behavioral activity of rats of different ages, and the effect of methylphenidate on the behavioral activity. The behavioral activity of Wistar male rats was measured on the nine hole-board apparatus. In experiment I, the behavioral activity of rats from three age groups (4, 8 and 12 weeks old) were measured in terms of the activity time, specific exploratory behavior, diverse exploratory behavior and defecation number. The rats were re-exposed to the hole-board again every two weeks until they 14 weeks old. The younger rats showed higher activity level compared to the older rats. The activity level decreased as the rats grew older. The younger rats also showed more diverse exploratory behavior, but less specific exploratory behavior compared with the older rats. These suggested that the younger rats may be more hyperactive in nature, and less prone to focus on the specific targets. In experiment II, the methylphenidate (4 mg/kg, i.p.) injected rats showed higher activity level than the controls across the three age groups. The exploratory behavioral patterns were not significantly different among the three age groups. This suggests that the methylphenidate injection raises the motor activity level without affecting the exploratory tendency of rats.

Protein engineering of Aspergillus awamori glucoamylase to increase its pH optimum

To increase the pH optimum of glucoamylase (GA), five mutations-S411G, S411A, S411C, S411H and S411D--were designed to destabilize the carboxylate ion form of Glu400, the catalytic base, by removing or weakening the hydrogen bond between Ser411 and Glu400, and thereby raising its pK. The substitution of alanine, histidine and aspartate were also designed to study the additional effects of polarity and both positive and negative charges, respectively. S411G GA had catalytic efficiencies like those of wild-type GA for isomaltose, maltose and maltoheptaose hydrolysis at pH 4.4, while S411A and S411C GAs had 54-74% and S411H and S411D GAs had only about 6-12% of wild-type catalytic efficiencies. All five mutations increased the pH optimum in the enzyme-substrate complex, mainly by raising pK1 values. S411A is the best performing and most industrially promising of the pH mutants isolated to date. S411A GA increased the pH optimum by 0.8 units for both maltose and maltoheptaose hydrolysis while maintaining a high level of activity and catalytic efficiency. In hydrolysis of 28% DE 10 maltodextrin, S411A GA had a pH optimum of 7 compared with pH 5.6 for wild-type GA, and had higher initial rates of glucose production than wild-type GA at all pH values tested above pH 6.6.

Mutations to alter Aspergillus awamori glucoamylase selectivity. II. Mutation of residues 119 and 121

Mutations Ser119-->Glu, Ser119-->Gly, Ser119-->Trp, Gly121-->Ala and Gly121-->Ala/Ser411-->Gly were constructed in glucoamylase to change substrate specificity. Mutation Ser411-->Gly was already known to decrease glucoamylase selectivity toward isomaltose formation and to increase peak glucose yield. All mutated glucoamylases had slightly lower specific activities on maltose than on wild-type glucoamylase. Ser119-->Glu, Ser119-->Gly and Ser119-->Trp glucoamylases were about as active on isomaltose and DP 4-7 maltooligosaccharides as wild-type glucoamylase. Gly121-->Ala and Gly121-->Ala/Ser411-->Gly glucoamylases were less active. At 55 degrees C Ser119-->Glu, wild-type, Ser119-->Trp, Ser119-->Gly, Gly121-->Ala and Gly121-->Ala/Ser411-->Gly glucoamylases had progressively higher peak glucose yields, generally in the opposite order to their activities. There was also an inverse correlation between peak glucose yield and ratio of initial rate of isomaltose production from glucose condensation to that of glucose production from maltodextrin hydrolysis. The effect of mutations Gly121-->Ala and Ser411-->Gly was not additive in predicting the effect of the double mutation on the ratio or on peak glucose yield.

Mutations to alter Aspergillus awamori glucoamylase selectivity. I. Tyr48Phe49-->Trp, Tyr116-->Trp, Tyr175-->Phe, Arg241-->Lys, Ser411-->Ala and Ser411-->Gly

Glucoamylase mutations to reduce isomaltose formation from glucose condensation and thus increase glucose yield from starch hydrolysis were designed to produce minor changes in the active site at positions not totally conserved. Tyr175-->Phe and Ser411-->Gly glucoamylases had catalytic efficiencies on DP 2-7 maltooligosaccharides like those of wild-type glucoamylase, while the catalytic efficiencies of Tyr116-->Trp, Arg241-->Lys and Ser411-->Ala glucoamylases were reduced by about half and Tyr48Phe49-->Trp glucoamylase had little remaining activity. Tyr175-->Phe, Ser411-->Ala and Ser411-->Gly glucoamylases had decreased ratios of the initial rate of isomaltose formation from glucose condensation to that of glucose formation from maltodextrin hydrolysis at both 35 and 55 degrees C compared with wild-type glucoamylase. Arg241-->Lys glucoamylase had a very similar ratio, while Tyr116-->Trp glucoamylase had a higher ratio. The highest glucose yields from maltodextrin hydrolysis were by the mutant glucoamylases having the lowest ratios of initial rates of isomaltose formation to glucose formation and this predicted high glucose yields better than the ratio of catalytic efficiency for maltose hydrolysis to that for isomaltose hydrolysis.

Reaction patterns of islet-cell autoantibodies in Macaca nigra

Circulating islet-cell autoantibodies (ICAAs) that reacted specifically with cytoplasmic components have been found in the blood of prediabetic Macaca nigra. The three distinct reaction patterns observed involved the majority of islet cells throughout the islet; a moderate number of cells, mainly at the islet periphery and around the vasculature; and a few cells scattered throughout the islet. Pancreas sections incubated with sera containing ICAAs followed with peroxidase-conjugated antibody were then reacted with anti-insulin, antiglucagon, or antisomatostatin antisera. The pattern associated with most of the islet cells was shown to be reactive to beta cells and was termed B-ICAA; the pattern with cells at the periphery was identified as alpha cells (A-ICAA); and the scattered cells contained somatostatin (D-ICAA). None of the three islet hormones were able to block ICAA reaction after overnight incubation, so the ICAAs are not anti-islet hormone antibodies. The varied reactions with antigens of different secretory cells indicate release of a variety of immunogens from islet cells as they necrose and cause the formation of different ICAAs.

Immunohistochemical study of islet amyloid in diabetes mellitus

Amyloid was isolated from islets of amyloidotic pancreata of monkey and human beings by solubilization of non-amyloid materials from the pancreas and digestion of contaminating collagen and elastin. The resulting pellet was estimated to be greater than 90% pure islet amyloid. Antibodies specific for monkey islet amyloid and for monkey and human liver amyloid A (AA) were raised in rabbits. Immunohistochemical reaction using the peroxidase antiperoxidase method demonstrated that amyloidotic pancreas reacted with both anti-AA and anti-islet amyloid antibodies. Although the antibodies are specific toward antigens, they cross-react with tissues from human and monkeys. The immunochemical results suggest the possibility that more than one kind of amyloid is associated with islet amyloidosis, but that a significant portion of the islet amyloid is related to AA. Preliminary chemical analysis indicated that islet amyloid is enriched with hexosamines while AA contains both hexosamines and hexoses. Establishment of the islet amyloid composition(s) can give insight into its source and its role in diabetes in Macaca nigra and human beings.

Islet cell cytoplasmic antibodies in Macaca nigra

Islet cell antibodies (ICA) have been measured in mature Macaca nigra. Of 30 nondiabetic monkeys, 26 (87%) were ICA-negative; of 43 monkeys with evidence of mild to severe hormonal or glycemic abnormalities, 39 (91%) were ICA-positive. Pancreatic islets were examined from biopsy and autopsy sections to assess cell deterioration and amyloid infiltration. No ICA were found in 13 of 18 (72%) monkeys with no evidence of amyloid, whereas 30 of 35 (86%) monkeys with islet amyloid and concurrent cell deterioration were ICA-positive. Association of ICA with metabolic and islet abnormalities was significant at P less than or equal to 0.001. ICA were specific for the islet cells in pancreatic sections; plasma preincubated with insulin, glucagon, or acetone extracts of tissues retained their ICA-positive reaction. The relationships of ICA in older monkeys to the islet lesion and to metabolic abnormalities could be relevant to similar situations in aging diabetic persons.

Serum proteins of Macaca nigra. Identification and changes in nondiabetic and diabetic monkeys

Serum proteins of Macaca nigra were separated by agarose gel electrophoresis. Proteins identified were: albumin, alpha 1-globulin, alpha 2-macroglobulin, haptoglobin, beta 1C-globulin, and gamma 1- and gamma 2-globulins. Diabetic M. nigra had decreased gamma 2-globulin; borderline diabetics had increased beta 3-globulin.

Monoamine metabolites in the CSF of epileptic patients

To assess the possible role of amine neurotransmitters in human epilepsy, we measured metabolites of serotonin (5-hydroxyindoleacetic acid [5-HIAA]), dopamine (homovanillic acid [HVA]), and norepinephrine (3-methoxy-4-hydroxyphenylethylene glycol [MHPG]) in the lumbar cerebrospinal fluid (CSF) of patients with partial complex seizures and in neurologic controls. Untreated epileptic patients had lower concentrations of 5-HIAA and HVA in the lumbar CSF than the controls, but the differences were not statistically significant. Among epileptic patients receiving effective antiepileptic drug treatment, the HVA concentration was within the control range. Mean MHPG concentrations were similar in patients and controls. From the epileptic patients whose CSF was obtained at pneumoencephalography we obtained a second sample of CSF that was originally in the basal cisterns. No significant differences between treated and untreated patients were found for any of the three metabolites. The concentrations of HVA and 5-HIAA were higher in cisternal than in lumbar CSF, but there was no such gradient for MHPG.

Metabolism of monoamines and diamines in hyperthyroid and hypothyroid rats

The in vivo rates of catabolism of 14C-labelled pentylamine, ethylamine, putrescine, and cadaverine were studied in thyroidectomized rats and others made hyperthyroid by the daily administration of 0.2 mg of L-thyroxine per kilogram for 20--21 days. Hyperthyroid rats metabolized the monoamines at an accelerated rate; thyroidectomized animals oxidized pentylamine at a reduced rate. There was no effect of hypophysectomy on the rate of pentylamine oxidation. The in vitro monoamine oxidase (MAO) activity of liver was reduced in hyperthyroid rats and unchanged in those thyroidectomized; MAO activity in skeletal muscle was increased in the hyperthyroid rats and decreased in the hypothyroid rats. Because of the large mass of skeletal muscle compared with liver, it is considered that the changes in muscle MAO could play an important role in determining the rate of oxidation of pentylamine in vivo. The oxidation of the two diamines tested was not significantly affected by thyroidectomy; the rates were increased in the hyperthyroid rats, but the increase was significant only for cadaverine.