Novel selection method for engineered antibodies using the mechanism of Fv fragment stabilization in the presence of antigen

Although the heavy and light chain domains of some antibody variable region fragments (Fvs) readily dissociate under physiological conditions, the Fvs are stable in the presence of antigen. This 'antigen-driven Fv stabilization mechanism' was applied to the selection of clones with specificity toward target antigens. The results can be summarized as follows. (i) Some of the residues in the heavy chain complementarity determining region 2 (HCDR2) of anti-hen egg white lysozyme (HEL) monoclonal antibody HyHEL10 heavy chain variable region (VH) were randomized. (ii) The randomized VH fragments of HyHEL10 were displayed on a filamentous bacteriophage and mixed with the target antigen, before being applied to a light chain variable region (VL) which was immobilized on microtiter plates and subjected to selection by panning. (iii) After four rounds of panning, four clones that showed significant binding to human lysozyme (hL), which HyHEL10 recognized poorly, were selected from the HCDR2 library. (iv) The soluble Fv fragments selected were expressed in Escherichia coli, purified, and subjected to an inhibition assay of lysozyme enzymatic activities and an isothermal titration calorimetry. These Fv fragments had increased affinity toward hL, and thermodynamic analysis suggested that the reduced entropy loss due to binding by the replacement of residues in HCDR2 resulted in the higher hL binding activity.

Effects of 5-(N-aminohexyl)carbamoyl-2'-deoxyuridine on endonuclease stability and the ability of oligodeoxynucleotide to activate RNase H

To evaluate an endonuclease resistance property of oligodeoxynucleotides (ODNs) containing 5-(N-aminohexyl)carbamoyl-2'-deoxyuridines (Hs) and to elucidate whether a duplex consisting of the ODN analogue and its complementary RNA induces RNase H activity, the ODNs containing the deoxyuridine analogues, Hs, at intervals of one, two, three, four and five natural nucleosides were synthesized. From partial hydrolysis of these ODNs with nuclease S1 (an endonuclease), it was found that the ODNs became more stable towards nucleolytic hydrolysis by the enzyme as the number of H increased. Furthermore, to examine whether the duplexes composed of the ODNs containing Hs and their complementary RNAs are substrates for RNase H or not, the duplexes of these ODNs and their complementary RNA strands were treated with Escherichia coliRNase H. It was found that cleavage of the RNA strands by the enzyme was kinetically affected by the introduction of Hs into the duplexes.

[Study on coagulation fibrinolytic systems in predialysis patients with chronic renal failure--comparison between patients with chronic glomerulonephritis and patients with diabetic nephropathy]

To clarify the abnormalities of coagulation and fibrinolytic systems on predialysis patients with chronic renal failure, we measured indices of coagulation and fibrinolytic systems in 33 predialysis patients whose creatinine (Cr) levels were over 3.0 mg/dl. We termed twenty-four patients with chronic glomerulonephritis the "CGN group". We also termed nine patients wit diabetes mellitus the "DM group". We measured thrombin.antithrombin III complex (TAT), alpha 2-plasmin inhibitor plasmin complex (PIC), D-dimer, protein C, protein S, thrombomodulin (TM), vitronectin, tissue plasminogen activator.plasminogen activator inhibitor-1 complex (tPAI-C) in theses two groups. Furthermore, we measured the same indices after 6 months in the CGN group. As a result, the plasma levels of both TAT, PIC, TM/Cr ration in the DM group were significantly higher that those in the CGN group, changes in both protein S activities and plasma levels of tPAI-C were reduced significantly after 6 months. In conclusion, the abnormalities of coagulation and fibrinolytic systems in predialysis diabetic patients were stronger than those in predialysis patients with CGN. Furthermore, these abnormalities were worsened after 6 months in predialysis patients with chronic renal failure.

Cloning and expression of the rubredoxin gene from Desulfovibrio vulgaris (Miyazaki F)--comparison of the primary structure of desulfoferrodoxin

A gene encoding rubredoxin from Desulfovibrio vulgaris (Miyazaki F) was cloned and overexpressed in Escherichia coli. A 1.1-kilobase pair DNA fragment, isolated from D. vulgaris (Miyazaki F) by double digestion with SmaI and SalI, contained two genes, the rubredoxin gene (rub) and the desulfoferrodoxin gene (rbo) which was situated upstream of rub. The deduced amino acid sequence of desulfoferrodoxin was homologous to those from other strains and Cys residues that are responsible to bind irons were also conserved. The expression system for rub was constructed under the control of the T7 promoter in E. coli. The purified protein was soluble and had a characteristic visible absorption spectrum. Inductively coupled plasma-atomic emission analysis and electron paramagnetic resonance analysis of the recombinant rubredoxin revealed the presence of an iron ion in a distorted tetrahedral geometry that was the same as native D. vulgaris rubredoxin. In vitro NADH reduction analysis indicated that recombinant rubredoxin was active, and its redox potential was determined as -5 mV.

Role of salt bridge formation in antigen-antibody interaction. Entropic contribution to the complex between hen egg white lysozyme and its monoclonal antibody HyHEL10

For elucidation of the role of salt bridge formation in the antigen-antibody complex, the interaction between hen egg white lysozyme (HEL) and its monoclonal antibody HyHEL10, the structure of which has been well characterized and forms one salt bridge (Lys97 of HEL and Asp32 of HyHEL10 heavy chain variable region (VH)), was investigated. Asp32 of VH was substituted with Ala, Asn, or Glu by site-directed mutagenesis, and the interaction between HEL and the mutant fragments of the variable region of light chain was investigated by inhibition of the enzymatic activity of HEL and isothermal titration calorimetry. Inhibition assay indicated that these mutations lowered the inhibition only slightly. Thermodynamic study indicated that the negative enthalpic change in the interaction between each of the mutant variable regions of light chain and HEL was significantly increased, although the association constant was slightly decreased, suggesting that these mutations increased the entropy change upon antigen-antibody binding. These results indicate that the role of salt bridge formation in the HyHEL10-HEL interaction is to lower the entropic loss due to binding. In the mutant proteins, the numbers of residues that were perturbed structurally on binding increased, suggesting that the salt bridge suppresses excess structural movement of the antibody upon binding.

Open sandwich ELISA: a novel immunoassay based on the interchain interaction of antibody variable region

We describe an immunoassay that is based on the interchain interaction of separated VL and VH chains from a single chain antibody variable region. In the presence of antigen, the chains reassociate. VL fragments of anti-hen egg lysozyme (HEL) antibody HyHEL-10 were immobilized on microtiter plates. Samples were coincubated with an M13-displayed VH chain, and assayed with peroxidase-labeled anti-M13 antibody. Signal was detected in direct proportion to the amount of HEL in the sample. Wide dynamic range with < 15 ng/ml sensitivity was attained.

Study of antibody-antigen interaction through site-directed mutagenesis of the VH region of a hybrid phage-antibody fragment

An important aspect of the study of antibody structure-function relationships involves analysis of natural or synthetic mutations of antigen-combining sites. The anti-hen egg lysozyme monoclonal antibody HyHEL-10 has been a focus for antibody structure-function studies. We have displayed on bacteriophage of a hybrid single chain Fv, containing the light chain variable region of HyHEL-10 and the heavy chain variable region of a structurally related but functionally distinct antibody, AS32. By using a combination of site-directed mutagenesis, complementary determining region grafting and molecular modeling, we have identified a number of contact and non-contact residues that are important in the affinity of HyHEL-10 for lysozyme. In particular, the heavy chain variable region framework residue at position 94 was shown to be an important determinant of high-affinity binding. The phage display approach eliminates the need for purification of antibodies and, when used in combination with polymerase chain reaction for variable region sequence mutagenesis, facilitates the rapid generation and characterization of mutant antibodies.

Synthesis of alpha-helix-forming peptides by gene engineering methods and their characterization by circular dichroism spectra measurements

Two kinds of peptides which were considered to form alpha-helices were designed and characterized. One was "alpha(3)-peptide' with 21 residues comprising three repeats of the seven-residue sequence Leu-Glu-Thr-Leu-Ala-Lys-Ala. This peptide appeared to be amphipathic due to a hydrophobic surface of Leu residues and a hydrophilic surface of Lys and Glu residues, thus forming a bundle structure. The other was "alpha(3)-GPRRG-alpha(3) peptide' with 47 residues in which two alpha(3)-peptides were connected by the five-residue sequence Gly-Pro-Arg-Arg-Gly. The genes encoding these peptides were fused to the adenylate kinase gene via a methionine codon. The resulting fused protein was expressed as an inclusion body, and the peptides were purified after cleavage with BrCN. The stability of the peptides in various buffers was then examined by measuring their circular dichroism spectra. The alpha(3)-peptide showed concentration-dependent stabilization of the alpha-helix. Sedimentation equilibrium ultracentrifugation indicated that it formed a bundle structure composed of four polypeptide chains, and a dimer intermediate during oligomerization was also detected by analytical gel-filtration. The stability of the alpha(3)-peptide was decreased by shifting the pH to 2 or 12, due to electrostatic repulsion of charged residues. Thus, the alpha(3)-peptide was stabilized by increasing the ionic strength, particularly in acidic or alkaline buffer, through the masking of the repulsion by high salt concentration. In buffer of neutral pH and a high salt concentration, the alpha(3)-peptide at high concentration formed visible aggregates, due possibly to the exposed hydrophobic surfaces of the alpha-helical bundles. On the other hand, alpha(3)-GPRRG-alpha(3) peptide did not show concentration-dependent reversible dissociation and association. It was shown to exist as a trimer even at low concentration, indicating very tight association of the alpha(3)-GPRRG-alpha(3) peptide. In contrast to the alpha(3)-peptide, the alpha(3)-GPRRG-alpha(3) peptide was very stable at various pH values and salt concentrations. This seemed to be due to increased hydrophobic interactions resulting from the increase in the number of seven-residue repeats from three to six, even though each group of three repeats was separated by a five-residue sequence.

A stable phage-display system using a phagemid vector: phage display of hen egg-white lysozyme (HEL), Escherichia coli alkaline, phosphatase, and anti-HEL monoclonal antibody, HyHEL10

A stable expression system for displaying the pIII fusion protein on the surface of a filamentous phage was constructed. A phagemid pIII display vector, pLUCK, was constructed by inserting the gene encoding the pIII fusion protein in the opposite direction to that of the lac promoter of pTZ18U. Using this phage display system, two enzymes, hen egg-white lysozyme (HEL) and E. coli alkaline phosphatase, and the single-chain Fv fragment of anti-HEL monoclonal antibody HyHEL10, could be stably and functionally displayed. Northern and primer extension analyses showed that a small amount of the sense mRNA encoding pIII-fused HEL was transcribed from the minor phage promoter located in the region encoding the C-terminus of pIII. Repressed expression of the pIII fusion protein can lead to the display of a wide range of proteins on filamentous phages without the need for strict expression conditions.

Effects of amino acid substitutions in the hydrophobic core of alpha-lactalbumin on the stability of the molten globule state

Five mutant alpha-lactalbumins, with one or two amino acid substitution(s) in the B helix, were engineered to examine the relation between the stability of the molten globule state and the hydrophobicity of these amino acids. The mutation sites (Thr29, Ala30 and Thr33) have been chosen on the basis of comparison of the amino acid sequences of goat, bovine and gunea pig alpha-lactalbumin, in which the guinea pig protein shows a remarkably more stable molten globule than the other proteins. The recombinant proteins were expressed Escherichia coli and then purified and refolded efficiently to produce the active proteins. The stability of the molten globule state of these engineered proteins has been investigated by urea-induced unfolding transition under an acidic condition (pH 2.0), where the molten globule state is stable in the absence of urea. The results show that the molten globule state is stabilized by the amino acid substitutions which raise the hydrophobicity of the residues, suggesting that the hydrophobic core in a globular protein plays an important role in the stability of the molten globule state. The change in stabilization free energy of the molten globule state caused by each amino acid substitution has been evaluated, and molecular mechanisms of stabilization of the molten globule state are discussed.

Human cystatin A is inactivated by engineered truncation. The NH2-terminal region of the cysteine proteinase inhibitor is essential for expression of its inhibitory activity

A series of NH2-terminal truncated forms of human cysteine proteinase inhibitor, cystatin A, was prepared by genetic engineering using Escherichia coli harboring mutated genes. Each variant of cystatin A was efficiently expressed as a fused protein with porcine adenylate kinase and released by CNBr degradation after exchange of the sole inner Met to Leu. The mutant cystatin A lacking an amino-terminal Met residue (called standard variant starting from Ile2, CystA2-98(M65L) showed the same inhibitory activity as authentic one isolated from human epidermis. Two-residue truncation scarcely influenced the activity, but further truncations deleting Pro3 and beyond conservative Gly4 and Gly5 caused a remarkable decrease of their inhibitory activity. But little effect was observed by a substitution of Pro3 with Leu. The loss of the activity by amino-terminal truncation was compensated slightly by engineered substitution of Gly75 with His on a second loop. In the two-dimensional 15N-1H HSQC NMR spectrum, four-residue truncation was found to cause changes in the chemical shifts of Val47 and Val48, which locate on a first loop and consist of a conservative QVVAG sequence. Furthermore, the truncation led to a change in fluorescence spectroscopic behavior of Trp75, which was introduced as a probe on the second loop. Fluorescence intensity of the Trp of the truncated (5-98) form was more affected by heating than the active standard variant. Conversely, fluorescence of Trp75 in 2-98 form was more quenched by acrylamide than the 5-98 variant. Thus, the amino-terminal region of cystatin A is essential for the expression of its inhibitory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of Tyr residues in the contact region of anti-lysozyme monoclonal antibody HyHEL10 for antigen binding

It has been shown that Tyr residues are unusually localized in the regions of antibodies responsible for contact with antigens (Padlan, E. A. (1990) Proteins Struct. Funct. Genet. 7, 112-124). In order to clarify the role of these Tyr residues in antigen binding, the interaction between hen egg white lysozyme (HEL) and its monoclonal antibody HyHEL10, whose structure has been well studied in complex with its antigen, was investigated. Four Tyr residues in the VH chain (HTyr-33, HTyr-50, HTyr-53, and HTyr-58) were replaced with Ala, Leu, Phe, or Trp, and the interactions between these mutant Fv fragments and HEL were studied by inhibition assay of the enzymatic activity of HEL and isothermal titration calorimetry. Twelve mutant Fv fragments could be expressed, but two mutants (HY50W and HY58W) could not be obtained in the Escherichia coli expression system, and a further two mutants (HY33A and HY50A) could not be purified by affinity chromatography. It was shown by inhibition assay that Tyr residues at each mutated site made positive contributions to the interaction to different degrees. Thermodynamic studies showed that the role of Tyr residues in antigen binding was to obtain enthalpic energy. The roles of Tyr residues in antibody HyHEL10 for the association with antigen, HEL, can be summarized as follows: 1) formation of hydrogen bonds by the hydroxyl group, 2), creating more favorable interactions through the aromatic ring and decreasing the entropic loss upon binding, and 3) allowing hydrophobic interaction through the side chain. The four Tyr residues studied here were found to play significant roles in the association in various ways.

Dissection of protein-carbohydrate interactions in mutant hen egg-white lysozyme complexes and their hydrolytic activity

Trp62 in the binding subsite B of hen egg-white lysozyme shows general features often observed in protein-carbohydrate interactions including a stacking interaction and a hydrogen bonding network with water molecules. A previous report by our group showed that the perturbation of these interactions by substitution of Trp62 with tyrosine or phenylalanine affects the substrate binding modes and also enhances the hydrolytic activity. In order to elucidate the relationship between structural and functional changes of these protein-carbohydrate interactions, the Trp62Tyr and Trp62Phe mutants complexed with the substrate analogue, (GlcNAc)3, were analyzed at 1.8 A resolution by X-ray crystallography. The overall structures of the mutant enzymes are indistinguishable from that of the wild type enzyme. Although the wild-type enzyme binds (GlcNAc)3 in only one binding mode (A-B-C), the Trp62Tyr mutant binds (GlcNAc)3 in two binding modes (A-B-C, B-C-D) and the Trp62Phe mutant has an even weaker binding mode. The aromatic rings of Tyr62 and Phe62 maintain their interactions with the carbohydrate molecules, but make fewer stacking interactions with the GlcNAc in the B site than the wild-type enzyme does. The hydroxyl group of Tyr62 interacts weakly with a water molecule which mediates hydrogen bonding in the GlcNAc residues in the B and C sites. The C-6 hydroxyl group of the GlcNAc residue in the C site rotates around the C-5-C-6 bond to complete the hydrogen bond network in the Trp62Tyr mutant-(GlcNAc)3 complex. On the other hand, this hydrogen bonding network does not form in the Trp62Phe mutant-(GlcNAc)3. In addition to these structural studies, the kinetic parameters of the hydrolysis of 4-methylumbelliferyl N-acetyl-chitotriose, ((GlcNAc)3-MeU), have been determined in order to further characterize the enzymatic properties of these mutant lysozymes. This demonstrates that the modulation of the hydrogen bonding network, including the flexible part of the carbohydrate and water molecules and/or the slight reduction of stacking interaction in the B site, alters the binding mode toward the carbohydrate and induces an enhancement of the hydrolytic activity.

A gene encoding a cytochrome c oxidase-like protein is located closely to the cytochrome c-553 gene in the anaerobic bacterium, Desulfovibrio vulgaris (Miyazaki F)

The gene encoding cytochrome c-553 from Desulfovibrio vulgaris (Miyazaki F) was cloned using a synthetic oligodeoxyribonucleotide probe. The nucleotide sequence indicated that cytochrome c-553 was synthesized as a precursor protein with an NH2-terminal signal sequence of 23 residues. In the cloned DNA fragment, there are three other open reading frames whose products have 191, 157, 541 amino acid residues, respectively. The putative ORF-4 product is highly homologous with the cytochrome c oxidase subunit I from various organisms.

Escape of red blood cells through gaps in glomerular basement membrane in a patient with mixed connective tissue disease

Hematuria in patients with glomerulonephritis seems to result from the passage of red blood cells through anatomical gaps in the glomerular basement membrane. However, such morphological evidence has rarely been demonstrated. A patient with mixed connective tissue disease associated with membranous glomerulonephritis is described in whom the renal biopsy specimen showed an escape of red blood cells through a gap in the basement membrane. These findings support the morphological basis of hematuria in glomerulonephritis.

Contribution to antibody-antigen interaction of structurally perturbed antigenic residues upon antibody binding

For elucidating the contribution of structurally perturbed antigenic residues upon antibody binding to antigen-antibody interaction, the interaction between hen egg white lysozyme (HEL) and HyHEL10 Fv fragment, which is one of several monoclonal antibodies against HEL and structurally well defined (Padlan, E.A., Silverton, E. W., Sheriff, S., Cohen, G. H., Smith-Gill, S. J., and Davies, D. R. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 5938-5942), was investigated. Asp-101 and Trp-62 of HEL, whose conformations are perturbed by the binding of antibody HyHEL10 in this interaction, were replaced with Gly, and the resulting interactions were studied by assay of the inhibition of the lysozyme activity with the Fv fragment and by titration calorimetry. The results can be summarized as follows. 1) It was possible to prepare the fully functional Fv fragment of HyHEL10 using a secretory expression system in Escherichia coli. Its inhibition profile for HEL activity was almost indistinguishable from that of HyHEL10 IgG, and the contribution of enthalpy to driving the interaction was shown to be significant. 2) A thermodynamic study of the interaction between the D101G mutant HEL and the Fv fragment revealed that, although the negative enthalpy change was smaller than that for the wild type, the Gibbs energy was almost identical to that of the wild type, which resulted from the smaller entropy loss. 3) Study of the interaction between the W62G mutant HEL and this Fv fragment indicated that the rotation of the Trp-62 indole ring upon binding of the antibody made an enthalpic contribution to antibody-antigen interaction, although Trp-62 of HEL was proposed not to be the direct contact residue in the HyHEL10.HEL complex. 4) From these results, it was confirmed experimentally that structural perturbations of antigenic residues upon antibody binding of antigen would contribute to the gain of enthalpic energy, in spite of partial offset by entropic loss, and to driving the interaction.

Effect of the order of antibody variable regions on the expression of the single-chain HyHEL10 Fv fragment in E. coli and the thermodynamic analysis of its antigen-binding properties

In order to physically stabilize the Fv fragment of anti-lysozyme monoclonal antibody, HyHEL10, the variable domains were linked covalently with a flexible linker. A marked difference in the level of expression in E. coli was observed between VH-linker-VL (scFvHL) and VL-linker-VH (scFvLH). The highly expressed scFvLH was purified by a single step of affinity chromatography from the culture supernatant with a typical yield of 3-5 mg per liter of culture. This HyHEL10 scFvLH showed reduced binding activity toward its antigen, HEL, in comparison with Fv. Thermodynamic study showed that this reduced activity was due to entropic loss upon binding to its antigen, although this interaction between scFvLH and its antigen was enthalpically favorable.

Secretory production of chicken ovomucoid domain 3 by Escherichia coli and alteration of inhibitory specificity toward proteases by substitution of the P1 site residue

Ovomucoids are commonly present in bird egg white and exhibit inhibitory activity toward various serine proteases. To investigate the structure-function relationship of ovomucoid domain 3, we established a secretory expression system for the chicken ovomucoid domain 3 (OMCHI3)-encoding gene in Escherichia coli by ligating it downstream from the tac promoter and signal peptide of E. coli alkaline phosphatase. E. coli JM105 was transformed with the resulting plasmid and induced with 1 mM isopropyl-beta-D-thiogalactopyranoside (IPTG). The mature OMCHI3 was detected in the culture supernatant, and was purified to homogeneity by three-step chromatography. Amino-acid sequence analysis showed that processing by the signal peptidase was carried out exactly at the expected site. Measurements of circular dichroism spectra and inhibitory activity indicated that OMCHI3 was produced in the properly folded form. Furthermore, site-specific replacement of the Ala residue at the P1 site with Met or Lys resulted in acquisition of inhibitory activity toward chymotrypsin or trypsin, respectively, indicating that the P1 site is the predominant determinant for inhibitory specificity.

Substrate specificity of tRNA (adenine-1-)-methyltransferase from Thermus thermophilus HB27

tRNA (adenine-1-)-methyltransferase was purified to homogeneity from an extreme thermophile, Thermus thermophilus HB27, by several steps of column chromatographies. The molecular weight of this enzyme was about 60,000 as analyzed by SDS polyacrylamide gel electrophoresis. Km for E. coli tRNA(2Glu) was 100 nM and that for the methyl group donor, S-adenosyl-L-methionine, was 7.8 microM. The substrate specificity of the enzyme was investigated by using T7 RNA polymerase transcripts and tRNA fragments obtained by partial digestion with RNases. The enzyme was able to transfer the methyl group to the 3'-half fragment of E. coli initiator tRNA, however, the extent of methylation was elevated by more than five times when the 5'-half fragment was added and annealed to the 3'-half. This indicates that the main recognition site of the enzyme is within the 3'-half region of tRNA molecule, while the tertiary interaction between the T-loop and the D-loop is very effective for the adequate methylation reaction.

Functional and structural role of a tryptophan generally observed in protein-carbohydrate interaction. TRP-62 of hen egg white lysozyme

In order to elucidate the role of the aromatic ring in recognition of the sugar ring, Trp-62 of hen egg white lysozyme, which is proposed on the basis of x-ray crystallography data to make contact with a sugar ring through van der Waals interaction, was replaced with aliphatic amino acids (Leu, Ile, Val, and Ala) and Gly by site-directed mutagenesis. In spite of the loss of the aromatic effect, these mutant lysozymes, except for the Trp-62-->Gly mutant, showed higher bacteriolytic activity than the wild-type lysozyme. Furthermore, the Trp-62-->Gly mutant still retained appreciable bacteriolytic activity. On the other hand, by these replacements, the enzymatic activities toward non-charged substrates were markedly reduced. Additionally, the side-chain structure of position 62 was found to be largely responsible for recognition of a saccharide ring in its active site cleft. NMR analysis of the Trp-62-->Leu and Trp-62-->Gly mutants indicated that the structural effects of Trp-62 replacements were localized in the loop region around position 62 and the part of the beta-sheet containing the hydrogen bonding network important for enzymatic activity. Thus, we conclude that Trp-62 not only interacts with oligosaccharide through van der Waals contact, but also maintains the local structural conformation to produce the lysozyme-oligosaccharide interaction.

Novel FMN-binding protein from Desulfovibrio vulgaris (Miyazaki F). Cloning and expression of its gene in Escherichia coli

A gene encoding a novel FMN-binding protein from Desulfovibrio vulgaris (Miyazaki F) was cloned, and its expression system was constructed in Escherichia coli. The 1.4-kilobase pair DNA fragment isolated from D. vulgaris (Miyazaki F) by double digestion with KpnI and SmaI was found to express a protein binding FMN as a prosthetic group under control of the lac promoter in E. coli. This DNA fragment contained several putative open reading frames. The partial amino acid sequence of the polypeptide portion of the purified FMN-binding protein and its tryptic peptides were completely consistent with those deduced from the nucleotide sequence of the third open reading frame in the cloned SmaI-SmaI fragment of D. vulgaris (Miyazaki F) DNA, which may include promoter and regulatory sequences. The nucleotide sequence of FMN-binding protein indicated that the protein is composed of 122 amino acids including an initiator Met residue and lacks a signal peptide for secretion. The main redox potential of the FMN-binding protein was measured as -325 mV using direct current cyclic and differential pulse voltammetric techniques and an electroreflectance method, suggesting that this FMN-binding protein functions as a redox protein like other FMN-binding proteins. Immunoblot analysis of the whole proteins from D. vulgaris (Miyazaki F) clearly indicated that this protein is expressed in this bacteria. However, the protein was found to have a primary structure distinct from those of other FMN-binding proteins and to be the smallest FMN-binding protein yet reported.

High-level expression of porcine muscle adenylate kinase in Escherichia coli: effects of the copy number of the gene and the translational initiation signals

Porcine muscle adenylate kinase (ADK) was overproduced in Escherichia coli using the expression plasmid with double A-T-G codon at the translational starting site and the Shine-Dalgarno (SD) sequence 10 bp apart from the first A-T-G. We used the expression vectors pKK223-3 and pMK2. pMK2 is about 10-20 times larger in copy number than pK223-3. For both vectors, duplication of A-T-G was effective and the quantity of the expressed ADK from the double A-T-G plasmid was 2 approximately 4-fold more than that achieved when only one A-T-G was present. The amount of the produced ADK was maximum in the case of using pMK2 with double A-T-G. The overproduced ADK formed inclusion bodies in E. coli. It was solubilized in 6 M guanidine hydrochloride and refolded. Through two steps of column chromatography, ADK was purified. It has the same amino acid composition and grossly the same activity as that reported by Schirmer et al. (1970). Its amino acid sequence of the NH2-terminal region was identical with that deduced from the cDNA sequence including the NH2-terminal methionine.