Structural and Functional Properties of Hen Egg-white Lysozyme Deamidated by Protein Engineering

The structural and functional properties of lysozymes genetically deamidated at positions 103 (N103D) and 106 (N106D) were studied by a protein engineering technique. The wild-type and mutant lysozymes were expressed in Saccharomyces cerevisiae and purified from the cultivation medium in two steps by cation-exchange chromatography on CM-Toyopearl. The lytic activity of deamidated lysozymes was almost the same as that of wild lysozyme, although the optimal pH of activity was slightly shifted to lower pH by the deamidation. The Gibbs free energy changes of unfolding (delta G) at 20 degrees C for N103D and N106D were almost the same as that of wild-type. On the other hand, the structural flexibility of lysozymes, estimated by protease digestion, was significantly increased by the deamidation. The surface functional properties of deamidated lysozymes were considerably enhanced, compared to those of wild-type lysozyme. These results suggest that structural flexibility is an important governing factor in surface functional properties of proteins, regardless of their structural stability.

Bioassisted capture and release of nanoparticles on nanolithographed ZnO films

Using an artificial peptide library, we have identified a peptide that has strict selective affinity for ZnO surfaces. The binding affinity of the peptide on the ZnO surface can be controlled simply through changes in phosphate concentration at constant pH and temperature. In this study, we functionalized inorganic nanoparticles by orderly conjugating ZnO-binding peptides (ZnOBPs) on the surface of cadmium selenide (CdSe) nanoparticles and performed spontaneous and reversible nanopatterning of ZnOBP-displayed nanoparticles on lithographed ZnO films. Conjugation of ZnOBPs on CdSe nanoparticles caused spontaneous adsorption of the nanoparticles on a ZnO film, and fluorescence and cathodoluminescence images clearly showed specific adsorption of nanoparticles on the ZnO films lithographed on nano- and micrometer scales. The selectively bound nanoparticles on ZnO films were completely released by changing the phosphate concentration in solution; such release did not require heat or mechanical applications. Repeated capture and release of nanoparticles were achieved on the micrometer scale. Our results show the potential of material-binding peptides for nanopatterning and dynamic microarrays.

A new diagnostic test for VLCAD deficiency using immunohistochemistry

BACKGROUND

Muscle pathology is often unhelpful in elucidating the specific underlying abnormality in patients with metabolic myopathy with rhabdomyolysis, including very-long chain acyl-CoA dehydrogenase (VLCAD) deficiency. Biochemical analyses require large amounts of biopsy samples for each enzyme assay.

OBJECTIVE

To develop a more efficient diagnostic method for VLCAD deficiency.

METHODS

The authors performed immunohistochemical analysis using an antibody to VLCAD on muscles from 344 patients (226 men and 118 women) without a specific diagnosis who had at least one of the following symptoms: myoglobinuria, high CK level, muscle pain, muscle stiffness, sudden infant death syndrome, and Reye-like syndrome.

RESULTS

Immunoreactivity to VLCAD was absent or markedly reduced in 13 patients. Biochemical analyses confirmed that all these patients had low enzymatic activity and reduced amount of protein. They all had the myopathic phenotype. The authors identified homozygous or compound heterozygous mutations in all of them. All recombinant proteins had reduced enzymatic activity except for 128G>A (G43D) and 796C>G (P266A) mutants, indicating that they are neutral polymorphisms.

CONCLUSIONS

The new screening method for the detection of VLCAD deficiency using an immunohistochemical technique identified 13 new Japanese patients with VLCAD deficiency.

Mutated SEA-D227A-conjugated antibodies greatly enhance antitumor activity against MUC1-expressing bile duct carcinoma

For the purpose of establishing a new adoptive immunotherapy for bile duct carcinoma (BDC), we have directed our attention to superantigens (SAgs), the most potent known activators of T lymphocytes. In our previous study, staphylococcal enterotoxin A (SEA) was conjugated chemically with MUSE11 mAb, which recognizes the MUC1 cancer-associated antigen, and shown to enhance the specific cytotoxic activity of T-LAK cells against MUC1-expressing BDC cells (TFK-1) in vitro and in vivo. However, it is probable that SEA might cause side-effects because of nonspecific binding to class II positive cells. In order to overcome these, we generated mutated SEA (mSEA) by changing Asp at position 227 of native SEA to Ala, which has reduced affinity to MHC class II molecules, but retains the potential for T cell activation. When mSEA-D227A was administered to rabbits to examine effects on blood pressure, 500 times more mSEA-D227A was tolerated than native SEA. This prompted us to construct a mSEA-D227A-conjugated mAb, reactive with MUC1. It augmented the antitumor activity of T-LAK cells significantly, and furthermore, mSEA-D227A could be conjugated to two bispecific antibodies, BsAb (anti-MUC1 x anti-CD3) and BsAb (anti-MUC1 x anti-CD28), which in combination had greater enhancing effects than mSEA-D227A-conjugated anti-MUC1 mAb, and combination of unconjugated BsAbs. These findings indicate a utility of mSEA-D227A-conjugated antibodies for targeted cancer immunotherapy.

A visualization method of filamentous phage infection and phage-derived proteins in Escherichia coli using biotinylated phages

Direct visualization of filamentous phage infection in Escherichia coli (E. coli) was attempted using biotinylated phages (BIO-phages). The biotinylation of the phages did not influence their infectivity into E. coli. E. coli infected with BIO-phages could be detected by using fluorescein-conjugated avidin with confocal laser scanning microscopy, and BIO-phages and BIO-phage-derived proteins in E. coli could be directly observed by using the avidin-biotin-peroxidase complex method with electron microscopy. This is the first report of direct visualization of phage infection and phage-derived proteins in the host cell using a biotin-avidin interaction. This simple and powerful method is applicable to the study of infection by various viruses.

HIV Rev peptides conjugated with peptide nucleic acids and their efficient binding to RRE RNA

HIV Rev peptides conjugated with peptide nucleic acids (PNAs) were designed and synthesized to develop a designing approach for a novel RNA-binding molecule. The binding affinities of PNA-peptides with the Rev responsive element (RRE) RNA were determined by the competition assay using a rhodamine-labeled Rev. The peptide conjugated with an antisense PNA (TGCGC) bound RRE RNA more efficiently than the molecule without the PNA or the peptide sequence.

Contribution of Thr29 to the thermodynamic stability of goat alpha-lactalbumin as determined by experimental and theoretical approaches

The Thr29 residue in the hydrophobic core of goat alpha-lactalbumin (alpha-LA) was substituted with Val (Thr29Val) and Ile (Thr29Ile) to investigate the contribution of Thr29 to the thermodynamic stability of the protein. We carried out protein stability measurements, X-ray crystallographic analyses, and free energy calculations based on molecular dynamics simulation. The equilibrium unfolding transitions induced by guanidine hydrochloride demonstrated that the Thr29Val and Thr29Ile mutants were, respectively, 1.9 and 3.2 kcal/mol more stable than the wild-type protein (WT). The overall structures of the mutants were almost identical to that of WT, in spite of the disruption of the hydrogen bonding between the side-chain O-H group of Thr29 and the main-chain C=O group of Glu25. To analyze the stabilization mechanism of the mutants, we performed free energy calculations. The calculated free energy differences were in good agreement with the experimental values. The stabilization of the mutants was mainly caused by solvation loss in the denatured state. Furthermore, the O-H group of Thr29 favorably interacts with the C=O group of Glu25 to form hydrogen bonds and, simultaneously, unfavorably interacts electrostatically with the main-chain C=O group of Thr29. The difference in the free energy profile of the unfolding path between WT and the Thr29Ile mutant is discussed in light of our experimental and theoretical results.

Replacing factor-dependency with that for lysozyme: affordable culture of IL-6-dependent hybridoma by transfecting artificial cell surface receptor

Cytokines and growth factors are indispensable for the propagation and maintenance of factor-dependent mammalian cells. However, cytokines are often so expensive that the use of factor-dependent cells for industrial applications such as protein production is often not practical. Based on our previous design of a binary hen egg lysozyme (HEL)-specific receptor composed of portions of the anti-HEL antibody and the erythropoietin receptor, a new pair of chimeric receptors having the intracellular domain of gp130 were made and transfected to an interleukin-6 (IL-6)-dependent hybridoma, 7TD1. The clone expressing the two new receptors showed clear HEL dose-dependent cell growth and monoclonal antibody production in both serum-based and serum-free media without IL-6. These results establish the feasibility of applying receptor design to tailor cells for the inexpensive induction of cell growth for the purpose of producing therapeutic products.

Nitric oxide system is involved in glomerular hyperfiltration in Japanese normo- and micro-albuminuric patients with type 2 diabetes

Glomerular hyperfiltration plays a pathogenic role in the early stages of diabetic nephropathy. Experimental studies in laboratory animals suggest that nitric oxide (NO) might be involved in the pathogenesis of glomerular hyperfiltration. We performed a cross-sectional study to determine the relationship between diabetic glomerular hyperfiltration and the NO system. Normoalbuminuric (n=41), microalbuminuric (n=25), and macroalbuminuric (n=16) patients with type 2 diabetes were recruited in this study and compared with age-matched 84 non-diabetic control subjects. Creatinine clearance and urinary NO(2)(-)/NO(3)(-) excretion (urinary NOx) were measured, and the expression of endothelial cell nitric oxide synthase (ecNOS) was evaluated in human renal tissues. Glomerular hyperfiltration was present in 19 (37.5%) and nine (36.6%) of normoalbuminuric and microalbuminuric type 2 diabetic patients, respectively. The urinary NOx was significantly higher in normoalbuminuric patients compared with normal subjects. Creatinine clearance correlated significantly with urinary NOx in normoalbuminuric and microalbuminuric patients. Immunohistochemical staining intensities for ecNOS were significantly increased in glomerular endothelial cells of microalbuminuric type 2 diabetic patients as compared with the control subjects. These results suggest that NO may contribute to the pathogenesis of glomerular hyperfiltration in Japanese type 2 diabetic patients.

A growth signal with an artificially induced erythropoietin receptor-gp130 cytoplasmic domain heterodimer

We report a strategy for generating efficient signal transduction with unnatural heterologous receptor combinations. As previously described [Ueda, H., Kawahara, M. et al. (2000) J. Immunol. Methods 241, 159-170], chimeric receptors composed of the V(H)/V(L) domains of anti-hen egg lysozyme antibody HyHEL-10 and N-terminally truncated erythropoietin receptor (EpoR) can be activated by lysozyme. When the cytoplasmic domains of these receptors were substituted with one derived from gp130, IL-3 dependent Ba/F3 cells expressing both V(H)-gp130 and V(L)-gp130 grew dose-dependently when given lysozyme without IL-3. However, cells expressing the heterologous pair of V(H)-gp130 and V(L)-EpoR also showed more efficient and stricter lysozyme-dependent proliferation in the absence of IL-3, indicating this combination is as an efficient and strict signal transducer as wild-type EpoR. The immunoprecipitation data indicated the existence of a preformed V(H)-gp130 and V(L)-EpoR heterodimer in the absence of lysozyme, suggesting the crucial role of a receptor conformational change in signal triggering as well as wild-type EpoR and gp130. Phosphorylation of JAK2, STAT3, and STAT5 was observed upon the addition of lysozyme, suggesting the activation of both EpoR- and gp130-derived signals.

Immunoreactivity to monoclonal antibody, Hep Par 1, in human hepatocellular carcinomas according to histopathological grade and histological pattern

We evaluated the immunoreactivity to monoclonal antibody for hepatocyte (Hep Par 1) and determined the cellular distribution of the antigen in hepatocellular carcinoma (HCC), based on the histopathological grade and histological pattern. The pathological material included 100 areas selected at random in 61 tissue sections from 12 autopsy livers with HCC. Immunoreactivity was classified into four categories; strongly positive (>90% of the area showed positive staining), moderately positive (5-90% of the area), weakly positive (<5% of the area), and negative (completely negative). All 19 (100%) well-differentiated, trabecular type HCC areas were strongly positive for Hep Par 1. Among 11 well-differentiated, pseudoglandular type HCC areas, 2 (18%) were strongly positive, 5 (46%) were moderately positive, 2 (18%) were weakly positive, and 2 (18%) were negative. Among 36 moderately differentiated, trabecular type HCC areas, 6 (17%) were strongly positive, 17 (47%) were moderately positive, 9 (25%) were weakly positive, and 4 (11%) were negative. None of the four moderately differentiated, pseudoglandular type HCC areas were strongly positive, 3 (75%) were moderately positive, 0 was weakly positive, and 1 (25%) was negative. Among 25 poorly differentiated, compact or trabecular type HCC areas, 15 (60%) were weakly positive and 10 (40%) were negative. All 5 (100%) undifferentiated HCC areas were negative for Hep Par 1. Our results indicate that immunoreactivity to Hep Par 1 in HCC decreases with reduced differentiation of the tumor, suggesting that Hep Par 1 monoclonal antibody is useful as a marker for the diagnosis and differentiation of HCCs.

Structural evidence for entropic contribution of salt bridge formation to a protein antigen-antibody interaction: the case of hen lysozyme-HyHEL-10 Fv complex

A structural and thermodynamic study of the entropic contribution of salt bridge formation to the interaction between hen egg white lysozyme (HEL) and the variable domain fragment (Fv) of anti-HEL antibody, HyHEL-10, was carried out. Three Fv mutants (HD32A, HD96A, and HD32AD96A) were prepared, and the interactions between the mutant Fvs and HEL were investigated. Crystallography revealed that the overall structures of these mutant complexes were almost identical to that of wild-type Fv. Little structural changes were observed in the HD32AD96A mutant-HEL complex, and two water molecules were introduced into the mutation site, indicating that the two water molecules structurally compensated for the complete removal of the salt bridges. This result suggests that the entropic contribution of the salt bridge originates from dehydration. In the singly mutated complexes, one water molecule was also introduced into the mutated site, bridging the antigen-antibody interface. However, a local structural difference was observed in the HD32A Fv-HEL complex, and conformational changes occurred due to changes in the relative orientation of the heavy chain to the light chain upon complexation in HD96A Fv-HEL complexes. The reduced affinity of these single mutants for the antigen originates from the increase in entropy loss, indicating that these structural changes also introduced an increase in entropy loss. These results suggest that salt bridge formation makes an entropic contribution to the protein antigen-antibody interaction through reduction of entropy loss due to dehydration and structural changes.

Cloning and expression of the catalase gene from the anaerobic bacterium Desulfovibrio vulgaris (Miyazaki F)

We identified a gene encoding a catalase from the anaerobic bacteria Desulfovibrio vulgaris (Miyazaki F), and the expression of its gene in Escherichia coli. The 3.3-kbp DNA fragment isolated from D. vulgaris (Miyazaki F) by double digestion with EcoRI and SalI was found to produce a protein that binds protoheme IX as a prosthetic group in E. coli. This DNA fragment contained a putative open reading frame (Kat) and one part of another open reading frame (ORF-1). The amino acid sequence of the amino terminus of the protein purified from the transformed cells was consistent with that deduced from the nucleotide sequence of Kat in the cloned fragment of D. vulgaris (Miyazaki F) DNA, which may include promoter and regulatory sequences. The nucleotide sequence of Kat indicates that the protein is composed of 479 amino acids per monomer. The recombinant catalase was found to be active in the decomposition of hydrogen peroxide, as are other catalases from aerobic organisms, but its K(m) value was much greater. The hydrogen peroxide stress against D. vulgaris (Miyazaki F) induced the activity for the decomposition of hydrogen peroxide somewhat, so the catalase gene may not work effectively in vivo.

Inhibition of the hepatitis C virus NS3 protease activity by Fv fragment of antibody 8D4

An antibody variable domain fragment (Fv) is a candidate for a specific inhibitor of the hepatitis C virus (HCV) NS3 protease. Here we report the functional characterization of the Fv of antibody 8D4, which is specific for the active site of the HCV NS3 protease domain. The variable fragments of 8D4 in the forms of Fv and scFv (VH-(G(4)S)(3)-VL) were expressed as insoluble fractions in the periplasm of Escherichia coli, and were subsequently solubilized, purified under denaturing conditions, and refolded. The Fv had an inhibition profile almost identical to that of the parent IgG, with an IC(50) of 71.3 nM, whereas the scFv had a greatly decreased affinity to NS3 and was the same as the isolated VH fragment. To date, this is the first report of an antibody Fv fragment specific for the HCV NS3 protease domain, aimed at designing potent protease inhibitors and antiviral drugs.

Demonstration of a homogeneous noncompetitive immunoassay based on bioluminescence resonance energy transfer

We describe a noncompetitive homogeneous bioluminescent immunoassay based on the antigen-dependent reassociation of antibody variable domains (open sandwich bioluminescent immunoassay, OS-BLIA). The reassociation of two chimeric proteins, an antibody heavy-chain fragment (V(H))-Renilla luciferase (Rluc) and an antibody light-chain fragment (V(L))-enhanced yellow fluorescent protein (EYFP), was monitored by a bioluminescence resonance energy transfer (BRET) between the two. Upon simple mixing of the reagents with the sample, an antigen-dependent increase in BRET was observed with a measurable concentration range of 0.1 to approximately 10 microg/ml antigen hen egg lysozyme. Compared with our comparable assays based on fluorescence resonance energy transfer (FRET), a 10-fold improvement in the sensitivity was attained, probably due to a reduction in reagent concentration.

Panning of a phage VH library using nitrocellulose membranes: application to selection of a human VH library

We have established a method for selecting binding phages from a phage immunoglobulin heavy chain variable region (VH) library by panning with nitrocellulose membranes (membrane panning). To evaluate the concentrating ability of membrane panning for binding phages, a phage VH library containing clones that bind to hen egg white lysozyme (HEL) was used for panning against HEL. The efficiency of our method was as high as that of panning with magnetic beads. In addition, we performed membrane panning against target proteins and isolated the binding phages. The human VH genes of these phages were cloned and expressed as VH-bacterial alkaline phosphatase (PhoA) conjugates (VH-PhoA) in Escherichia coli. The dose-dependent binding of VH-PhoA to target proteins was confirmed by dot blotting. When applied to disease-associated antibodies, these methods will likely benefit clinical research. In addition, these techniques may be applicable to systematic analysis in proteome studies.

Folding-unfolding of goat alpha-lactalbumin studied by stopped-flow circular dichroism and molecular dynamics simulations

Folding reaction of goat alpha-lactalbumin has been studied by stopped-flow circular dichroism and molecular dynamics simulations. The effects of four single mutations and a double mutation on the stability of the protein under a native condition were studied. The mutations were introduced into residues located at a hydrophobic core in the alpha-domain of the molecule. Here we show that an amino acid substitution (T29I) increases the native-state stability of goat alpha-lactalbumin against the guanidine hydrochloride-induced unfolding by 3.5 kcal/mol. Kinetic refolding and unfolding of wild-type and mutant goat alpha-lactalbumin measured by stopped-flow circular dichroism showed that the local structure around the Thr29 side chain was not constructed in the transition state of the folding reaction. To characterize the local structural change around the Thr29 side chain to an atomic level of resolution, we performed high-temperature (at 400 K and 600 K) molecular dynamics simulations and studied the structural change at an initial stage of unfolding observed in the simulation trajectories. The Thr29 portion of the molecule experienced structural disruption accompanied with the loss of inter-residue contacts and with the water molecule penetration in the 400-K simulation as well as in four of the six 600-K simulations. Disruption of the N-terminal portion was also observed and was consistent with the results of kinetic refolding/unfolding experiments shown in our previous report.

Construction of a diabody (small recombinant bispecific antibody) using a refolding system

Diabodies are the recombinant bispecific antibodies (BsAbs), constructed from heterogeneous single-chain antibodies. Usually, diabodies have been prepared from bacterial periplasmic fraction using a co-expression vector (i.e. genes encoding two chains were tandemly located under the same promoter). Some diabodies, however, cannot be expressed as a soluble material owing to inclusion body formation, which limits the utilization of diabodies in various fields. Here we report an improved method for the construction of diabodies using a refolding system. As a model, a bispecific diabody binding to adenocarcinoma-associated antigen MUC1 and to CD3 on T cells was studied. One chain consisted of a VH specific for MUC1 linked to a VL specific for CD3 with a short polypeptide linker (GGGGS). The second was composed of a VL specific for MUC1 linked to a VH specific for CD3. The two hetero scFvs were independently obtained from intracellular insoluble fractions of Escherichia coli, purified, mixed stoichiometrically (at an equivalent molar ratio of 1:1) and refolded. The refolded two hetero scFv has a hetero-dimeric structure, with complete specificity for both target cells [i.e. MUC1 positive cells and CD3 positive lymphokine-activated killer cells with a T cell phenotype (T-LAK)]. Evaluation of the in vitro efficacy of T-LAK with the diabody by growth inhibition assay of cancer cells demonstrated maximum growth inhibition of cancer cells to reach approximately 98% at an effector:target ratio (E:T ratio) of 10, almost identical with that with anti-MUC1xanti-CD3 chemically synthesized BsAbs (c-BsAbs). This is the first report of the construction of a diabody using a refolding system.

Cell-growth control by monomeric antigen: the cell surface expression of lysozyme-specific Ig V-domains fused to truncated Epo receptor

Previously we have shown that the V(H) and V(L) fragments of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 are weakly associated but can be driven together by antigen. By joining these antibody variable domains to the cytoplasmic portion of the murine erythropoietin receptor, we created a chimeric growth factor receptor that could be activated by HEL. After co-transfection with two plasmids encoding the respective chimeric receptors in IL-3 dependent murine pro-B Ba/F3 cells, a portion of the cells survived under antigen dependent stimulation without IL-3. These surviving cells all showed coexpression of the two chimeric receptor chains and demonstrated HEL dose-dependent growth stimulation without IL-3. When another IL-3 dependent cell line 32D was transfected with a variant of such chimeric receptor with a linker peptide (Gly-Ser-Gly) inserted between V(H)/V(L) and EpoR domains, an improved growth response was attained. These observations suggest the utility of heterodimeric Fv chimeric receptors in creating cells that respond to monomeric antigen.

Functional Fv fragment of an antibody specific for CD28: Fv-mediated co-stimulation of T cells

The most predominant co-stimulation pathway, which is critical for T cell activation and proliferation, is the CD28-B7 pathway. The anti-CD28 monoclonal antibody (mAb) also provides a co-stimulatory signal to T cells. In order to construct a functional Fv fragment (complex of VH and VL domains) of anti-CD28 antibody using a bacterial expression system, cDNA encoding the variable regions of immunoglobulin from 15E8 hybridoma cells was cloned and expressed in Escherichia coli. The Fv fragment was obtained as a soluble protein from the periplasmic fraction and showed a binding pattern similar to parental IgG. The Fv fragment induced proliferation of peripheral blood mononuclear cells in the presence of anti-CD3 or anti-CD2 mAb and enhanced anti-tumor activity of anti-MUC1x(anti)-CD3 bispecific antibody when tested with lymphokine-activated killer cells with T cell phenotype. Thus, the anti-CD28 Fv fragment will be promising not only for the study of co-stimulation, but also for cancer immunotherapy.

Design of artificial pepetides that recognize the HIV RRE IIB RNA

Peptide nucleic acid (PNA) conjugated peptides, derived from HIV-1 Rev, were designed and synthesized in order to construct molecules that recognize HIV RRE IIB RNA. The competitive binding analyses using fluorescent Rev peptide revealed that the PNA unit on the peptide affected the RNA binding.

Isolation and characterization of monoclonal antibodies that inhibit hepatitis C virus NS3 protease

A series of mouse monoclonal antibodies (MAbs) to the nonstructural protein 3 (NS3) of hepatitis C virus was prepared. One of these MAbs, designated 8D4, was found to inhibit NS3 protease activity. This inhibition was competitive with respect to the substrate peptide (K(i) = 39 nM) but was significantly decreased by the addition of the NS4A peptide, a coactivator of the NS3 protease. 8D4 also showed marked inhibition of the NS3-dependent cis processing of the NS3/4A polyprotein but had virtually no effect on the succeeding NS3/4A-dependent trans processing of the NS5A/5B polyprotein in vitro. Epitope mapping of 8D4 with a random peptide library revealed a consensus sequence, DxDLV, that matched residues 79 to 83 (DQDLV) of NS3, a region containing the catalytic residue Asp-81. Furthermore, synthetic peptides including this sequence were shown to block the ability of 8D4 to bind to NS3, indicating that 8D4 interacts with the catalytic region of NS3. The data showing decreased inhibition potency of 8D4 against the NS3/4A complex suggest that 8D4 recognizes the conformational state of the protease active site caused by the association of NS4A with the protease.

Fluorolabeling of antibody variable domains with green fluorescent protein variants: application to an energy transfer-based homogeneous immunoassay

A site-specific and efficient fluorolabeling of antibody variable regions with green fluorescent protein (GFP) variants and its application to an energy transfer-based homogeneous fluoroimmunoassay (open sandwich FIA) were attempted. Two chimeric proteins, Trx-V(H)-EBFP and Trx-V(L)-EGFP, consisting of V(H) and V(L) fragments of anti-hen egg lysozyme (HEL) antibody HyHEL-10 and two GFP color variants, EBFP and EGFP, respectively, were designed to be expressed in cytoplasm of trxB - mutant Escherichia coli as fusions with thioredoxin from E.coli The mixture of two proteins could be purified with HEL-affinity chromatography, retaining sufficient intrinsic fluorescence and binding activity to HEL. A significant increase in fluorescence resonance energy transfer (FRET) dependent on HEL concentration was observed, indicating the reassociation of the V(H) and V(L) domains of these chimeric proteins due to co-existing antigen. With this open sandwich FIA, an HEL concentration of 1-100 microg/ml could be non-competitively determined. The assay could be performed in a microplate format and took only a few minutes to obtain a sufficient signal after simple mixing of the chimeric proteins with samples. This represents the first demonstration that the FRET between GFP variants is applicable to homogeneous immunoassay.

Thermodynamic consequences of grafting enhanced affinity toward the mutated antigen onto an antibody. The case of anti-lysozyme antibody, HyHEL-10

In order to address the mechanism of enhancement of the affinity of an antibody toward an antigen from a thermodynamic viewpoint, anti-hen lysozyme (HEL) antibody HyHEL-10, which also recognize the mutated antigen turkey lysozyme (TEL) with reduced affinity, was examined. Grafting high affinity toward TEL onto HyHEL-10 was performed by saturation mutagenesis into four residues (Tyr(53), Ser(54), Ser(56), and Tyr(58)) in complementarity-determining region 2 of the heavy chain (CDR-H2) followed by selection with affinity for TEL. Several clones enriched have a Phe residue at site 58. Thermodynamic analyses showed that the clones selected had experienced a greater than 3-fold affinity increase toward TEL in comparison with wild-type Fv, originating from an increase in negative enthalpy change. Substitution of HyHEL-10 HTyr(58) with Phe led to the increase in negative enthalpy change and to almost identical affinity for TEL in comparison with mutants selected, indicating that mutations at other sites decrease the entropy loss despite little contribution to the affinity for TEL. These results suggest that the affinity of an antibody toward the antigen is enhanced by the increase in enthalpy change by some limited mutation, and excess entropy loss due to the mutation is decreased by other energetically neutral mutations.

Functional construction of the anti-mucin core protein (MUC1) antibody MUSE11 variable regions in a bacterial expression system

A bacterial expression system for the variable region fragments (Fvs) of the anti-MUC1 tumor antigen antibody MUSE11 has been constructed. The Fv fragment showed binding specificity toward TFK-1 cells, with slightly reduced affinity compared to its parent IgG. The single-chain Fv fragment was arranged in two orders, VH-linker-VL and VL-linker-VH. However, linking the regions with a flexible peptide linker (GGGGS)(3) or with a shorter linker (GGGGS) led to a dramatic decrease in the biological activity toward the target antigen in both arrangements, suggesting that the MUSE11 antibody loses its activity when the domains are linked with polypeptide linkers. These results indicate that the variable region domains of the anti-MUC1 antibody MUSE11 have specificity only in the Fv form, and that linking the domains strongly reduces the association with its target antigen. Gel filtration analysis indicates that the scFv has a dimeric structure, suggesting that the inactivation of MUSE11 scFv is due to unfavorable intermolecular associations of the scFv chains. To our knowledge, this is the first report of a significant reduction in affinity caused by linking the variable domains in both arrangements, i.e., VH-VL and VL-VH.

Functional domain-assembly in hairpin ribozymes

Functional structures of hairpin ribozymes have been investigated by constructing various chemically modified molecules. Domain-exchange and linker insertion experiments were performed to find active conformations of the RNA enzyme showing cleavage activity. Our experiments and other evidence suggest that the active structure has a bent conformation, and that domain-interactions are essential for the cleavage activity.

Construction of HIV Rev peptides containing peptide nucleic acid that bind HIV RRE IIB RNA

Peptides containing peptide nucleic acid (PNA) have been designed and synthesized to construct molecules recognizing a bulge or a loop structure of RNA. Such peptides were here designed from the HIV Rev protein that can bind the stem-loop IIB of the Rev responsive element (RRE) RNA. Variations of PNA modulated the binding affinities of the peptides to RRE IIB RNA.

Refolding of therapeutic proteins produced in Escherichia coli as inclusion bodies

Overexpression of cloned or synthetic genes in Escherichia coli often results in the formation of insoluble protein inclusion bodies. Within the last decade, specific methods and strategies have been developed for preparing active recombinant proteins from these inclusion bodies. Usually, the inclusion bodies can be separated easily from other cell components by centrifugation, solubilized by denaturants such as guanidine hydrochloride (Gdn-HCl) or urea, and then renatured through a refolding process such as dilution or dialysis. Recent improvements in renaturation procedures have included the inhibition of aggregation during refolding by application of low molecular weight additives and matrix-bound renaturation. These methods have made it possible to obtain high yields of biologically active proteins by taking into account process parameters such as protein concentration, redox conditions, temperature, pH, and ionic strength.

Investigation of the recognition of an important uridine in an internal loop of a hairpin ribozyme prepared using post-synthetically modified oligonucleotides

We introduced 4-thio- ((4S)U), 2-thio- ((2S)U), 4- O -methyluridine ((4Me)U) and cytidine substitutions for U+2, which is an important base for cleavage in a substrate RNA. Oligonucleotides containing 4-thio- and 4- O -methyluridine were prepared by a new convenient post-synthetic modification method using a 4- O - p -nitrophenyl-uridine derivative. A hairpin ribozyme cleaved the substrate RNA with either C+2, (4S)U+2 or (4Me)U+2 at approximately 14-, 6- and 4-fold lower rates, respectively, than that of the natural substrate. In contrast, the substrate with a (2S)U+2 was cleaved with the same activity as the natural substrate. These results suggest that the O4 of U+2 is involved in hydrogen bonding at loop A, but the O2 of U+2 is not recognized by the active residues. Circular dichroism data of the ribozymes containing (4S)U+2 and (2S)U+2, as well as the susceptibility of the thiocarbonyl group to hydrogen peroxide, suggest that a conformational change of U+2 occurs during the domain docking in the cleavage reaction. We propose here the conformational change of U+2 from the ground state to the active molecule during the reaction.

Homogeneous noncompetitive immunoassay based on the energy transfer between fluorolabeled antibody variable domains (open sandwich fluoroimmunoassay)

The antigen-dependent stabilization of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 variable region was monitored with fluorescence resonance energy transfer (FRET) between fluorolabeled heavy chain (VH) and light chain (VL) fragments. The VH and VL fragments labeled with succinimide esters of fluorescein and rhodamine-X, respectively, were mixed in a cooled cuvette, and the change in fluorescence spectra upon antigen addition was monitored. When excited at 490 nm, significant decrease in the fluorescence at 520 nm and its increase at 605 nm were observed when an increasing amount of HEL was added to the mixture in the concentration range of 1-100 micrograms/mL. The assay, named open sandwich fluoroimmunoassay (FIA), is noncompetitive and homogeneous and can be conducted with one clone of antibody. With the use of appropriate antibodies, it is thought to be a quick and inexpensive alternative to the conventional laborious and/or expensive immunoassays.

Crystal structure of anti-Hen egg white lysozyme antibody (HyHEL-10) Fv-antigen complex. Local structural changes in the protein antigen and water-mediated interactions of Fv-antigen and light chain-heavy chain interfaces

In order to address the recognition mechanism of the fragments of antibody variable regions, termed Fv, toward their target antigen, an x-ray crystal structure of an anti-hen egg white lysozyme antibody (HyHEL-10) Fv fragment complexed with its cognate antigen, hen egg white lysozyme (HEL), was solved at 2.3 A. The overall structure of the complex is similar to that reported in a previous article dealing with the Fab fragment-HEL complex (PDB ID code,). However, the areas of Fv covered by HEL upon complex formation increased by about 100 A(2) in comparison with the Fab-HEL complex, and two local structural differences were observed in the heavy chain of the variable region (VH). In addition, small but significant local structural changes were observed in the antigen, HEL. The x-ray data permitted the identification of two water molecules between the VH and HEL and six water molecules retained in the interface between the antigen and the light chain complementarity determining regions (CDRs) 2 and 3 (CDR-L2 and CDR-L3). These water molecules bridge the antigen-antibody interface through hydrogen bond formation in the VL-HEL interface. Eleven water molecules were found to complete the imperfect VH-VL interface, suggesting that solvent molecules mediate the stabilization of interaction between variable regions. These results suggest that the unfavorable effect of deletion of constant regions on the antigen-antibody interaction is compensated by an increase in favorable interactions, including structural changes in the antigen-antibody interface and solvent-mediated hydrogen bond formation upon complex formation, which may lead to a minimum decreased affinity of the antibody Fv fragment toward its antigen.

Expression of a synthetic gene encoding canine milk lysozyme in Escherichia coli and characterization of the expressed protein

A high-expression plasmid of the canine milk lysozyme, which belongs to the family of calcium-binding lysozymes, was constructed in order to study its physico-chemical properties. Because the cDNA sequence of the protein has not yet been determined, a 400 base-pair gene encoding canine milk lysozyme was first designed on the basis of the known amino acid sequence. The gene was constructed by an enzymatic assembly of 21 chemically synthesized oligonucleotides and inserted into an Escherichia coli expression vector by stepwise ligation. The expression plasmid thus constructed was transformed into BL21(DE3)/pLysS cells. The gene product accumulated as inclusion bodies in an insoluble fraction. Recombinant canine milk lysozyme was obtained by purification and refolding of the product and showed the same characteristics in terms of bacteriolytic activity and far- and near-UV circular dichroism spectra as the authentic protein. The NMR spectra of refolded lysozyme were also characteristic of a native globular protein. It was concluded that recombinant canine milk lysozyme was folded into the correct native structure. Moreover, the thermal unfolding profiles of the refolded recombinant lysozyme showed a stable equilibrium intermediate, indicating that the molten globule state of this protein was extraordinarily stable. This expression system of canine milk lysozyme will enable biophysical and structural studies of this protein to be extended.

Open sandwich ELISA with V(H)-/V(L)-alkaline phosphatase fusion proteins

The Sandwich ELISA is a widely used technique to measure antigen concentration. Recently, a novel ELISA based on the interchain interaction of separated V(H) and V(L) chains from a single antibody variable region (Fv) was proposed (Open Sandwich ELISA). Since it employs a single antibody recognizing one epitope, the assay requires, in essence, only one cycle of incubation and washing steps. To demonstrate this directly, we have constructed a recombinant gene fusion encoding the V(H) chain of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 and Escherichia coli alkaline phosphatase (V(H)-PhoA). The same type of gene fusion using V(L) chain instead of V(H) chain (V(L)-PhoA) was also constructed and the proteins were obtained with an E. coli expression/secretion system. Open Sandwich ELISAs were performed using microtiter plates with immobilized V(L) or V(H) fragment, and V(H)-PhoA or V(L)-PhoA, respectively, as the detection reagent which was simultaneously added to each well with samples. As a result, HEL concentrations in the samples were determined after one round of incubation and washing steps, with a signal generated in a direct relationship to the concentration of HEL added to the reaction mixture. The minimum detectable HEL concentration was approximately 10 ng/ml, which was almost equal to the value previously obtained with plate-immobilized V(L) and V(H) fragment displayed on M13 phage. When the active-site mutant V(H)-PhoA(D101S) was employed instead of V(H)-PhoA and reacted at an optimum pH of 10, a significant enhancement in signal was attained.

SEA-scFv as a bifunctional antibody: construction of a bacterial expression system and its functional analysis

A SEA-antibody single chain Fv (SEA-scFv) fusion protein was produced by bacterial expression system in this study. SEA-scFv has both staphylococcal enterotoxin A (SEA) effects and antibody activity directed at the epithelial mucin core protein MUC1, a cancer associated antigen. It was expressed mostly in the cytoplasm as an insoluble form. The gene product was solubilized by guanidine hydrochloride, refolded by conventional dilution method, and purified using metal-chelating chromatography. The resulting SEA-scFv fusion protein preparation was found to react with MUC1 and MHC class II antigens and had the ability to enhance cytotoxicity of lymphokine activated killer cells with a T cell phenotype against a human bile duct carcinoma cell line, TFK-1, expressing MUC1. This genetically engineered SEA-scFv fusion protein promises to be an important reagent for cancer immunotherapy.

Cell-free expression of two single-chain monoclonal antibodies against lysozyme: effect of domain arrangement on the expression

Single-chain antibodies (scFv), which can be produced in Escherichia coli cells, have been shown in numerous cases to be active in antigen binding. In the case of the two anti-lysozyme single-chain antibodies, scFvLH and scFvHL, which have the reversed arrangement of the variable domains of the heavy and light chains of the corresponding monoclonal antibodies, the expression level differs greatly when they are produced in Escherichia coli [Tsumoto et al. (1995) Biochem. Biophys. Res. Commun. 201, 546-551]. Although the expression level of scFvLH is high in vivo, the single chain antibody with the reversed orientation (scFvHL) was synthesized in a very low yield and no active product could be obtained. We report here the synthesis of these two anti-lysozyme single-chain antibodies in high yields and with high biological activities in a cell-free E. coli expression system in the presence of reduced and oxidized glutathione, protein disulfide isomerase (PDI), and chaperones. In immunological blotting assays, the synthesized scFvs with both arrangements exhibit specific binding activity to the corresponding antigens, hen egg-white lysozyme, and in an activity assay both inhibited the action of lysozyme. scFvLH is synthesized mainly as a product with the expected molecular weight, whereas scFvHL is produced with additional shorter fragments, suggesting that the low yield isolation through the expression in vivo is due to mistranslation or ribonucleolytic cleavage of the transcript. In the cell-free expression of scFv a certain amount of the product is precipitated but in the presence of chaperones the amount of soluble protein increased from 25 to 90% (PDI and chaperones). The overall expression level and the specific biological activity, however, were hardly influenced. The system reported here can provide significant amounts of various scFv fragments regardless of the order of variable regions, including those which are hardly expressed in vivo.

Effect of the extra n-terminal methionine residue on the stability and folding of recombinant alpha-lactalbumin expressed in Escherichia coli

The structure, stability, and unfolding-refolding kinetics of Escherichia coli-expressed recombinant goat alpha-lactalbumin were studied by circular dichroism spectroscopy, X-ray crystallography, and stopped-flow measurements, and the results were compared with those of the authentic protein prepared from goat milk. The electric properties of the two proteins were also studied by gel electrophoresis and ion-exchange chromatography. Although the overall structures of the authentic and recombinant proteins are the same, the extra methionine residue at the N terminus of the recombinant protein remarkably affects the native-state stability and the electric properties. The native state of the recombinant protein was 3.5 kcal/mol less stable than the authentic protein, and the recombinant protein was more negatively charged than the authentic one. The recombinant protein unfolded 5.7 times faster than the authentic one, although there were no significant differences in the refolding rates of the two proteins. The destabilization of the recombinant protein can be fully interpreted in terms of the increased unfolding rate of the protein, indicating that the N-terminal region remains unorganized in the transition state of refolding, and hence is not involved in the folding initiation site of the protein. A comparison of the X-ray structures of recombinant alpha-lactalbumin determined here with that of the authentic protein shows that the structural differences between the proteins are confined to the N-terminal region. Theoretical considerations for the differences in the conformational and solvation free energies between the proteins show that the destabilization of the recombinant protein is primarily due to excess conformational entropy of the N-terminal methionine residue in the unfolded state, and also due to less exposure of hydrophobic surface on unfolding. The results suggest that when the N-terminal region of a protein has a rigid structure, expression of the protein by E. coli, which adds the extra methionine residue, destabilizes the native state through a conformational entropy effect. It also shows that differences in the electrostatic interactions of the N-terminal amino group with the side-chain atoms of Thr38, Asp37, and Asp83 bring about a difference in the pKa value of the N-terminal amino group between the proteins, resulting in a greater negative net charge of the recombinant protein at neutral pH.

Substrate recognition of tRNA (Guanosine-2'-)-methyltransferase from Thermus thermophilus HB27

Transfer RNA (guanosine-2'-)-methyltransferase (Gm-methylase, EC 2.1. 1.32) from Thermus thermophilus HB27 is one of the tRNA ribose modification enzymes. The broad substrate specificity of Gm-methylase has so far been elucidated using various species of tRNAs from native sources, suggesting that the common structures in tRNAs are recognized by the enzyme. In this study, by using 28 yeast tRNAPhe variants obtained by transcription with T7 RNA polymerase, it was revealed that the nucleotide residues G18 and G19 and the D-stem structure are essentially required for Gm-methylase recognition, and that the key sequence for the substrate is pyrimidine (Py)17G18G19. The other conserved sequences were found not to be essential, but U8, G15, G26, G46, U54, U55, and C56 considerably affected the methylation efficiency. These residues are located within a limited space embedded in the L-shaped three-dimensional structure of tRNA. Therefore, disruption of the three-dimensional structure of the substrate tRNA is necessary for the catalytic center of Gm-methylase to be able to access the target site in the tRNA, suggesting that the interaction of Gm-methylase with tRNA consists of multiple steps. This postulation was confirmed by inhibition experiments using nonsubstrate tRNA variants which functioned as competitive inhibitors against usual substrate tRNAs.

Highly efficient recovery of functional single-chain Fv fragments from inclusion bodies overexpressed in Escherichia coli by controlled introduction of oxidizing reagent--application to a human single-chain Fv fragment

An improved and efficient refolding system for a single-chain antibody fragment (scFv) from inclusion bodies expressed in Escherichia coli was developed. Stepwise removal of denaturing reagent and controlled addition of oxidizing reagent were found to be the most effective conditions to achieve for almost complete recovery of functional monomeric scFv from inclusion bodies. Adding L-arginine to the refolding solution also increased the yield of refolded functional scFv. The single-chain Fv fragments of both a mouse anti-lysozyme monoclonal antibody, HyHEL10, and a human monoclonal antibody against the D antigen of the Rh blood group, D10, in solubilized inclusion bodies could be refolded under these conditions with yields of up to 95%. The refolding procedures developed in this study will contribute to providing a stable supply of large amounts of human single-chain Fv fragments.

P1 specificity of aqualysin I (a subtilisin-type serine protease) from Thermus aquaticus YT-1, using P1-substituted derivatives of Streptomyces subtilisin inhibitor

Aqualysin I is an alkaline serine protease isolated from Thermus aquaticus YT-1, an extreme thermophile. We have measured the P1-specificity of aqualysin I, using wild-type and five P1-substituted derivatives of Streptomyces subtilisin inhibitor (SSI). SSIs efficiently inhibited the activity of aqualysin I, with low substrate specificity. Charge and hydrophobicity of side chain of the P1 amino acid residue showed no significant effect to the P1-specificity of this enzyme.

Calorimetric study of mutant human lysozymes with partially introduced Ca2+ binding sites and its efficient refolding system from inclusion bodies

During the process of evolution, ancestral lysozymes evolved into calcium-binding lysozymes by acquiring three critical aspartate residues at positions 86, 91 and 92. To investigate the process of the acquisition of calcium-binding ability, two of the aspartates were partially introduced into human lysozyme at positions 86, 91 and 92. These mutants (HLQ86D, HLA92D and HLQ86D/D91Q/A92D), having two critical aspartates in calcium-binding sites, were expressed in Escherichia coli as non-active inclusion bodies. For the preparation of lysozyme samples, a refolding system using thioredoxin was established. This system allowed for effective refolding of wild-type and mutant lysozymes, and 100% of activity was recovered within 4 days. The calcium ion dependence of the melting temperature (Tm) of wild-type and mutant lysozymes was investigated by differential scanning calorimetry at pH 4.5. The Tm values of wild-type, HLQ86D and HLA92D mutants were not dependent on calcium ion concentration. However, the Tm of HLQ86D/D91Q/A92D was 4 degrees higher in the presence of 50 mM CaCl2 than in its absence, and the calcium-binding constant of this mutant was estimated to be 2.25(+/-0.25)x10(2) M(-1) at pH 4.5. Moreover, the calcium-binding ability of this mutant was confirmed by the result using Sephadex G-25 gel chromatography. These results indicate that it is indispensable to have at least two aspartates at positions 86 and 92 for acquisition of calcium-binding ability. The process of the acquisition of calcium-binding site during evolution of calcium-binding lysozyme is discussed.

Structural and functional effect of Trp-62-->Gly and Asp-101-->Gly substitutions on substrate-binding modes of mutant hen egg-white lysozymes

In order to clarify the structural role of subsite B of hen egg-white lysozyme in hydrolytic activity towards a carbohydrate substrate, we analysed the structures of Trp-62-->Gly and Asp-101-->Gly mutant hen lysozymes, which have no side chain at positions 62 or 101, complexed with a substrate analogue, (N-acetyl-d-glucosamine)3 [(GlcNAc)3], using X-ray crystallography. The overall protein structures in the mutant lysozyme complexes were almost identical to those in the wild type. In the crystals of all the mutant complexes, the (GlcNAc)3 molecule, which is an inhibitor of wild-type lysozyme, had no inhibitory effect, but was hydrolysed as a substrate. One of the products, (GlcNAc)2, the reducing end of which is an alpha-anomer, was bound in an unproductive binding mode, protruding from the active-site cleft, and was able to act as an inhibitor. Hydrolysis of the synthetic substrate by the mutants occurred in a beta-anomer-retaining manner, and so the alpha-anomer product was converted from the beta-anomer product. Thus the interactions of Asp-101 and Trp-62 in subsite B are not essential for the catalytic mechanism, but co-operatively enhance the affinity of the substrate in the productive binding mode, other than the inhibitor in the unproductive mode.

Essentially minimal sequence for substrate recognition by tRNA (guanosine-2')-methyltransferase from Thermus thermophilus HB27

Transfer RNA (guanosine-2'-)-methyltransferase (Gm-methylase, EC.2.1.1.32) from extreme thermophile, Thermus thermophilus HB27 is one of the tRNA-ribose modification enzymes; this enzyme specifically catalyze the transfer of a methyl group from S-adenosyl-L-methionine to 2'-OH of the ribose of the guanosine at position 18 in tRNA. A broad substrate specificity of Gm-methylase was observed using natural tRNAs as methyl group acceptors, which suggests that some local stractures common in tRNAs are recognized by the enzyme. By using yeast tRNA(Phe) variants obtained by transcription of their genes with T7 RNA polymerase, it was revealed that the residues G18 and G19, as well as the D-stem structure were primarily required for the methylation reaction and that the essentially minimal sequence for the substrate was Pyrimidine17-G18-G19. The other conserved sequences and the tertiary base-pairs were not essential, but G15, G46, U55 and C56 strongly affected the methylation efficiency.

Cloning and expression of the gene encoding flavodoxin from Desulfovibrio vulgaris (Miyazaki F)

The gene encoding a flavodoxin of Desulfovibrio vulgaris (Miyazaki F) was cloned, and overexpressed in Escherichia coli. A 1.6-kbp DNA fragment, isolated from D. vulgaris (Miyazaki F) by double digestion with SalI and EcoRI, contained the flavodoxin gene and its regulatory region. An expression system for the flavodoxin gene under control of the T7 promoter was constructed in E. coli. The purified protein was soluble and exhibited a characteristic visible absorption spectrum. HPLC analysis of the recombinant flavodoxin revealed the presence of an identical FMN to that found in the native D. vulgaris flavodoxin, and its dissociation constant with FMN was determined to be 0.38 nM. In vitro H2 reduction analysis indicated that the recombinant flavodoxin is active, and its redox potential was determined to be E1 = -434 and E2 = -151 mV using methyl viologen and 2-hydroxy-1,4-naphthoquinone, respectively. Its redox behavior was also examined with the recombinant flavodoxin adsorbed onto a graphite electrode. The mutant, A16E, was also produced, which revealed the feature of a conserved Glu residue at the surface of the molecule.

Structural analysis of mutant hen egg-white lysozyme preferring a minor binding mode

Trp62 in hen egg-white lysozyme has general features observed in protein-carbohydrate interactions, a stacking interaction toward nonpolar surface of the substrate sugar residue B and a hydrogen bonding network with the residue C. Our previous report (I. Kumagai, K. Maenaka, F. Sunada, S. Takeda, K. Miura, Eur. J. Biochem. 212 (1993) 151-156.) showed that the substitution of Trp62 changed the substrate binding modes; especially, the Trp62His mutant exhibited the drastic change of the binding mode and preferred to a minor binding mode of the wild-type enzyme. In order to clarify the relationship between functional and structural changes of the Trp62His mutant, we analyzed the structure of the Trp62His mutant hen lysozyme complexed with the substrate analogue, (GlcNAc)3, by X-ray crystallography. The overall protein structure in the mutant lysozyme complex was almost identical to that in the wild-type. His62 shared almost the same plane as the indole ring of Trp62 of the wild-type. Although the (GlcNAc)3 molecule which is an inhibitor against the wild-type lysozyme was cocrystallized, the Trp62His mutant did not put it in the sites A-B-C but hydrolyzed it as a substrate. One of the products, (GlcNAc)2, whose reducing end is alpha-anomer, was bound in another binding mode sticking out from the active-site cleft. The hydrolytic activity against the synthetic substrate showed that the mutant was a beta-anomer retaining enzyme, so the alpha-anomer product was converted from the beta-anomer product. Therefore, the Trp62His mutant showed the remarkable change of the substrate binding modes not by alteration of the catalytic system but possibly by subtle rearrangement of general features of protein-carbohydrate interactions between His62 and the sugar residues B and C.

Construction of mono- and bivalent human single-chain Fv fragments against the D antigen in the Rh blood group: multimerization effect on cell agglutination and application to blood typing

An expression system for mono- and bivalent single-chain Fv fragments (scFv) of a human antibody against D antigen in the Rh blood group system was established in Escherichia coli. The cDNA encoding the Fv fragment of the anti-D monoclonal antibody D10 was cloned using the polymerase chain reaction and expressed in E.coli by fusing with a peptide tag link in the C-terminus of the light chain variable region. The scFv fragment expressed by the bacteria produced specific agglutination of human D positive red cells in the presence of an anti-peptide tag antibody. Flow cytometric analysis clearly indicated that the bacterially prepared scFv showed high specificity and affinity for D antigen, which was identical with that of the parental IgG. In order to construct bivalent D10 scFv for use in direct cell agglutination, the scFv was fused with a dimeric protein, bacterial alkaline phosphatase (BAP). The fusion protein produced significant agglutination of human red blood cells with D antigen, confirming that the bacterially expressed fusion protein is a functional bivalent antibody fragment. Specific agglutination of D positive red cells by D10 scFv-BAP was enhanced in the presence of anti-BAP antibody, suggesting that further multimerization of scFv led to highly efficient cell agglutination. By grafting BAP enzymatic activity into the scFv fragment (enzyme-linked scFv), blood typing could conveniently be performed. These results indicate that bacterially expressed scFv and scFv-BAP would be of practical use in blood typing. The system reported here could also be applied to the examination of other cell surface antigens and cell agglutination.