In vivo properties of an IgG3-IL-2 fusion protein. A general strategy for immune potentiation

In this report, we describe a strategy for enhancing the immunogenicity of a wide variety of Ags by linking them to IL-2 via an IgG3-IL-2 fusion protein with high affinity for a convenient hapten Ag, dansyl (DNS; N,N-dimethyl-1-aminonaphthalene-5-sulfonyl chloride). This fusion protein, anti-DNS-IgG3-IL-2, combines the functional characteristics of its constituents and has pharmacokinetic properties that are greatly improved over those of IL-2 and a previously described IgG1-IL-2 fusion. The molecule is intact and recoverable from the blood of mice hours after i.p. injection and reaches distant organs throughout the animal. The 7-h in vivo half-life of this molecule is much longer than that of IL-2, addressing a major obstacle in the application of IL-2 to human diseases, including cancer and AIDS. Additionally, the Ab's specificity for the hapten dansyl and the convenient chemistry of dansyl provide a means to link IL-2 to virtually any molecule of interest without the complexities and uncertainties of making IL-2 fusions with each molecule individually. Using hapten-conjugated-BSA (DNS-BSA) as a model Ag we show that the Ab response elicited by anti-DNS-IgG3-IL-2-bound DNS-BSA-Sepharose injected into mice is increased over that of DNS-BSA-Sepharose or anti-DNS-IgG3-bound DNS-BSA-Sepharose. Anti-DNS-IgG3-IL-2 also increased the Ab response to soluble DNS-BSA after a booster injection. This system should be useful in testing the ability of IL-2 to potentiate the immune response to Ag and in screening a large number of potential Ags for use in vaccines. The dramatically improved pharmacokinetics should also overcome one of the major difficulties in applying IL-2 to the treatment of human disease, its short half-life.

Mapping myosin-binding sites on actin probed by peptides that inhibit actomyosin interaction

A 2-kDa peptide (2K peptide) which was derived from the neck region of porcine aorta smooth muscle myosin heavy chain binds to actin competitively with skeletal myosin subfragment 1 (S1) in the absence of ATP and inhibits acto-S1 ATPase activity [Katoh, T. and Morita, F. (1993) J. Biol. Chem. 268, 2380-2388]. Using this and other peptides, myosin-binding sites on actin were mapped and their functions were studied. The 2K peptide inhibited the acto-S1 ATPase activity without inhibiting the binding of S1 to actin in the presence of ATP. On the other hand, the dansylated 2K peptide (DNS-2K peptide) inhibited not only the acto-S1 ATPase activity but also the binding of S1 to actin in the presence of ATP. Then, DNS-2K peptide was crosslinked to actin with 1-ethyl-3[3-(dimethylamino)propyl] carbodiimide. Amino acid composition and sequencing analyses of the fluorescent lysylendopeptidase-peptides of the crosslinked product indicated that DNS-2K peptide was crosslinked to acidic residues within residues 1-18 (Asp1, Glu2, Asp3, Glu4, and/or Asp11), 19-50 (Asp25), and 85-113 (Glu99 or Glu100) of actin. A competition experiment for the crosslinking with unlabeled 2K peptide showed that the crosslinking to residues 85-113 of actin was specific for DNS-2K peptide. In addition, isolated actin peptide 85-113 was found to show the competitive inhibition of actin-activated ATPase activity of S1 with respect to actin. These results suggest that the site within residues 1-28 of actin participates in the actin-activation of myosin ATPase activity, and the site within residues 85-113 of actin participates in the weak binding of myosin to actin in the presence of ATP.

Determination of L-buthionin (SR)-sulfoximine, gamma-glutamylcysteine synthetase inhibitor in rat plasma with HPLC after prelabeling with dansyl chloride

L-(SR)-Buthionin sulfoximine (L-(SR)-BSO) is a potent and specific inhibitor of gamma-glutamylcysteine synthetase, which catalyzes the first reaction of glutathione biosynthesis. A selective, sensitive, and simple high-performance liquid chromatographic method was developed for the determination of L-(SR)-BSO in rat plasma. After the compound was labeled with dansyl chloride (Dns-Cl) under optimal conditions, it was separated in a Zolbax-ODS column with a mobile phase that consisted of 0.01M phosphate buffer, methanol, and acetonitrile (8:1:3, v/v). The compound was detected with a fluorescence detector at an excitation wavelength of 335 nm and an emission wavelength of 525 nm using a xenon lamp. The coefficients of variation (DV) from the interassay in the low and high concentrations (10 and 500 micrograms/mL of L-(SR)-BSO in rat plasma) were 2.5 and 4.8%, respectively. The CVs from the intra-assay in the low and high concentrations were 3.2 and 5.6%, respectively. The minimum concentration of L-(SR)-BSO that could be determined was 10 micrograms/mL when 100-microL serum samples were used. The detection limit was 50 ng per injection volume. This method enables pharmacokinetic and pharmacodynamic studies in rats.

Identification of S-(2,3-dihydroxypropyl)cystein in a macrophage-activating lipopeptide from Mycoplasma fermentans

Mycoplasmas are capable of stimulating monocytes and macrophages to release cytokines, prostaglandins, and nitric oxide. The aim of this study was to characterize the chemical nature of the previously isolated [Mühlradt, P. F., & Frisch, M. (1994) Infect. Immun. 62, 3801-3807] macrophage-stimulating material "MDHM" from Mycoplasma fermentans. Mycoplasmas were delipidated, and MDHM activity was extracted with octyl glucoside and further purified by reversed-phase HPLC. Macrophage-stimulating activity was monitored by nitric oxide release from peritoneal macrophages from C3H/HeJ endotoxin low responder mice. HPLC-purified MDHM was rechromatographed on an analytic scale RP 18 column before and after proteinase K treatment. Proteinase treatment did not diminish biological activity but shifted MDHM elution toward higher lipophilicity, suggesting that the macrophage-stimulating activity might reside in the lipopeptide moiety of a lipoprotein. Proteinase K-treated MDHM was hydrolyzed, amino groups were dansylated, and the dansylated material was isolated by HPLC. Dansylated S-(2,3-dihydroxypropyl)cystein (glycerylcystein thioether), typical for Braun's murein lipoprotein, and Dns-Gly and Dns-Thr were identified by tandem mass spectrometry. These amino acids were isolated from biologically active but not from the neighboring inactive HPLC fractions. IR spectra from proteinase K-treated, HPLC-purified MDHM and those from the synthetic lipopeptide [2,3-bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-CysSerSer AsnAla were very similar. The data, taken together, indicate that lipoproteins of a nature previously detected in eubacteria are expressed in M. fermentans and that at least one of these lipoproteins and a lipopeptide derived from it constitute the macrophage-activating principle MDHM from these mycoplasmas.

Two-stage nucleotide binding mechanism and its implications to H+ transport inhibition of the uncoupling protein from brown adipose tissue mitochondria

The uncoupling protein (UCP) from brown adipose tissue mitochondria is the simplest H+ translocator known. H+ transport is regulated by fatty acids as activators and by pruine nucleotides as inhibitors. Nucleotide binding again is strongly influenced by the pH [Klingenberg, M. (1988) Biochemistry 27, 781-791]. Previously, by using fluorescent 2'-O-dansyl (DANS) derivatives of purine nucleotides, a two-stage binding mechanism was unraveled with a slow transition from a loose into a tight conformational state in the isolated UCP [Huang, S.-G., & Klingenberg, M. (1995) Biochemistry 34, 349-360]. Whereas with the unsubstituted nucleotides the transition to the tight state is nearly complete, various DANS and DAN (dimethylaminonaphthoyl) nucleotides bind more to the loose state. Here we investigated the relationships between the two-stage nucleotide binding and the inhibition of the H+ transport activity in reconstituted proteoliposomes. Further, limited tryptic digestion was used as an indicator of conformational change induced by the nucleotide binding in the isolated protein. The inhibition of H+ transport activity in reconstituted UCP proteoliposomes correlated only with the fraction of tight state of nucleotide binding. Unsubstituted nucleotides (ATP, GTP, and ADP) as well as DANSGTP inhibit fully the H+ transport, whereas DANSATP and DANSADP inhibit only to about 50%, and DANSAMP is nearly ineffective. Even for the loose conformational state the nucleotide derivatives exhibit considerable affinity. This allows DANSAMP to replace prebound ATP from UCP and relieve the inhibition of H+ transport by reversing the distribution of UCP from the tight into the loose conformational state. The pH dependence of the fraction of nucleotide binding in the tight state correlates closely with the pH dependence of the degree of H+ transport inhibition. Titration with DANS nucleotides of UCP incorporated into phospholipid vesicles revealed that over 70% of binding sites had an affinity comparable with that for the isolated UCP while the remaining sites displayed substantially lower affinity, due to nonhomogeneity of the reconstituted system. The sensitivity against trypsin digestion is inversely correlated with the fraction of nucleotide binding in the tight state. Whereas unsubstituted nucleotides and DANSGTP protect strongly against trypsinolysis, DANSATP and DANSADP do only partially, and DANSAMP does not at all. The counteracting influences of the DANS substitution are shown with DANSAMP, which has an affinity comparable to that of DANSATP or DANSADP but cannot form the tight inhibited complex. These data show that nucleotide binding only in the tight state is associated with a strong conformational change, which further causes an inhibition of H+ transport. In conclusion, UCP can exist in a loose noninhibited and a tight inhibited conformational state. The equilibrium between these two conformations is shifted to the tight state with unsubstituted nucleotides but remains to variable degrees in the loose state with DANS and DAN derivatives. The DANS group hinders progressively the transition to the tight state as the binding affinity of the underlying nucleotide decreases.

High-performance liquid chromatographic assay for tryptase based on the hydrolysis of dansyl-vasoactive intestinal peptide

A rapid, sensitive, semiautomated method to measure the activity of mast cell-derived tryptase has been developed. The assay is based on the tryptase-mediated hydrolysis of vasoactive intestinal peptide that was modified to include an N-terminal dansyl reporter group. Tryptase cleaves vasoactive intestinal peptide (VIP) producing two major and two minor products. Full-length VIP was separated from the proteolysis products by reverse-phase (C18) chromatography. The amount of each product as well as the amount of full-length substrate remaining was determined using an in-line fluorescence detector. As little as 0.5 pmol of peptide could be detected. Predominant cleavages were after Arg-14 and Lys-20 with minor cleavages after Lys-15 and Lys-21. The hydrolysis of VIP at Arg-14 was slightly affected by the presence of the dansyl group at the N-terminus. While the Km value was unaffected, the kcat value decreased, yielding a kcat/Km ratio that was eightfold lower. The addition of calcium chloride to the reaction mixture resulted in a slight decrease in the kcat/Km ratio. Cleavage of dansyl-VIP by tryptase was completely inhibited by DesPro2-Arg15-Aprotinin.

High-performance liquid chromatographic evaluation of biogenic amines in foods. An analysis of different methods of sample preparation in relation to food characteristics

Biogenic amines are compounds formed by amino acid decarboxylation in fermented foods. Most of the methods for amine determination involve acid extraction followed by a liquid-liquid purification step. The different parameters which can influence amine recoveries are considered; experience with different foods such as cheese, fish and meat preserves are reported and for each of them the optimized analytical procedure is described. Data concerning recovery and repeatability of the method are also reported and the various factors that influence amine extraction are discussed. The possibility of applying direct derivatization without any other purification step is also considered.

Mutations of recombinant rat liver fatty acid-binding protein at residues 102 and 122 alter its structural integrity and affinity for physiological ligands

Rat liver fatty acid-binding protein (FABP) is able to accommodate a wide range of non-polar anions in addition to long-chain fatty acids. This property means that the liver protein is functionally different from other FABPs from intestine, muscle and adipose tissue that have a more restricted ligand specificity and stoichiometry. The availability of crystal structures for the latter proteins has highlighted the importance of two arginine residues that are involved in the binding of the fatty acid carboxylate. Only one of these arginine residues, arginine-122, is conserved in liver FABP, whereas the other arginine, at position 102, is replaced by a threonine. In order to gain further insight into the nature of ligand interactions with liver FABP these key residues (102 and 122) have been changed by site-directed mutagenesis. The results with an R122Q mutant highlight the critical role of this arginine in determining ligand affinity, while similar but less dramatic effects were observed with the T102Q mutant. The double mutant T102Q/R122Q was expressed but had lost the ability to bind fluorescent ligands. It is concluded that Arg-122 plays a role in accommodating the carboxylate group of at least one fatty acid. It is proposed that physiological ligands with more bulky headgroups, such as lysophospholipids, acyl-CoA and mono-olein, bind with the headgroups in a solvent-exposed location near the portal region of the protein. The portal region is suggested to be more flexible in the mutants (R122Q and to a lesser extent T102Q). The net result is that the ligand specificity of the R122Q mutant changes to that of a protein with enhanced affinity for acyl-CoA, lysophospholipids and mono-olein.

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of human parotid salivary proteins: comparison of dansylation, coomassie blue R-250 and silver detection methods

Detection of human parotid salivary proteins by dansylation and UV-transillumination after sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) has been compared with Coomassie Blue R-250 and silver staining procedures. Dansylation gives superior results in terms of both resolution and sensitivity, especially with basic proline-rich proteins (PRPs).

Myosin-induced changes in F-actin: fluorescence probing of subdomain 2 by dansyl ethylenediamine attached to Gln-41

Actin labeled at Gln-41 with dansyl ethylenediamine (DED) via transglutaminase reaction was used for monitoring the interaction of myosin subfragment 1 (S1) with the His-40-Gly-42 site in the 38-52 loop on F-actin. Proteolytic digestions of F-actin with subtilisin and trypsin, and acto-S1 ATPase measurements on heat-treated F-actin revealed that the labeling of Gln-41 had a stabilizing effect on subdomain 2 and the actin filaments. DED on Gln-41 had no effect on the values of K(m) and Vmax of the acto-S1 ATPase and the sliding velocities of actin filaments in the in vitro motility assays. This suggests either that S1 does not bind to the 40-42 site on actin or that such binding is not functionally important. The binding of monoclonal antidansyl IgG to DED-F-actin did not affect acto-S1 binding in the absence of nucleotides, indicating that the 40-42 site does not contribute much to rigor acto-S1 binding. Myosin-induced changes in subdomain 2 on actin were manifested through an increase in the fluorescence of DED-F-actin, a decrease in the accessibility of the probe to collisional quenchers, and a partial displacement of antidansyl IgG from actin by S1. It is proposed that these changes in the 38-52 loop on actin originate from S1 binding to other myosin recognition sites on actin.

Isocratic high-performance liquid chromatographic method for quantitative determination of lysine, histidine and tyrosine in foods

A method for the quantitative determination of lysine, histidine and tyrosine in foods based on pre-column derivatization with 5-dimethylaminonaphthalene-1-sulfonyl chloride (DnsCl) and reversed-phase liquid chromatography has been developed. Derivatization conditions, including DnsCl concentration, time, temperature, and buffer solution were studied. To establish the reliability of the proposed liquid chromatographic (LC) method, the precision and accuracy of the analyses were evaluated using samples of casein and lysozyme.

Conformational changes in subdomain 2 of G-actin: fluorescence probing by dansyl ethylenediamine attached to Gln-41

Gln-41 on G-actin was specifically labeled with a fluorescent probe, dansyl ethylenediamine (DED), via transglutaminase reaction to explore the conformational changes in subdomain 2 of actin. Replacement of Ca2+ with Mg2+ and ATP with ADP on G-actin produced large changes in the emission properties of DED. These substitutions resulted in blue shifts in the wavelength of maximum emission and increases in DED fluorescence. Excitation of labeled actin at 295 nm revealed energy transfer from tryptophans to DED. Structure considerations and Cu2+ quenching experiments suggested that Trp-79 and/or Trp-86 serves as energy donors to DED. Energy transfer from these residues to DED on Gln-41 increased with the replacement of Ca2+ with Mg2+ and ATP with ADP. Polymerization of Mg-G-actin with MgCl2 resulted in much smaller changes in DED fluorescence than divalent cation substitution. This suggests that the conformation of loop 38-52 on actin is primed for the polymerization reaction by the substitution of Ca2+ with Mg2+ on G-actin.

Formation of membrane domains created during the budding of vesicular stomatitis virus. A model for selective lipid and protein sorting in biological membranes

Vesicular stomatitis virus buds from domains of the plasma membrane that have a unique protein and lipid composition. Fluorescence digital imaging microscopy and resonance energy transfer were used to determine how the two viral envelope-associated proteins, the G and the M proteins, could alter the lateral distribution of lipids in large unilamellar vesicles and form domains. The G protein formed large domains in vesicles containing phosphatidic acid but not with phosphatidylserine, while the M protein formed domains enriched in both acidic phospholipids. Domains enriched in sphingomyelin were observed only when both the G protein and the M protein were present in vesicles containing phosphatidic acid. Phosphatidylcholine and gramicidin (chosen to represent a host membrane protein) were excluded from the domains. Cholesterol was induced to partition into the domains only in vesicles containing phosphatidic acid and sphingomyelin along with both of the proteins. Phosphatidylethanolamine was not enriched or depleted in the domains. Domains of similar composition were formed using vesicles made from dioleoylphospholipids and the lipids extracted from BHK-21 plasma membranes, indicating that the fatty acid composition was not as important as the polar head groups of the phospholipids. The phospholipid and cholesterol compositions of the domains formed by the G and the M proteins in vesicles were very similar to the composition of the viral envelope, suggesting that the domains represent the areas in the plasma membrane where the virus buds. This study provides a model for selective lipid and protein sorting that occurs in biological membranes.

Epitope mapping for monoclonal antibody against human surfactant protein A (SP-A) that alters receptor binding of SP-A and the SP-A-dependent regulation of phospholipid secretion by alveolar type II cells

Surfactant protein A (SP-A) is a lung-specific glycoprotein in pulmonary surfactant and has a collagen like sequence on its N-terminal. SP-A has been shown to function as an inhibitor of phospholipid secretion by primary culture of alveolar type II cells via cell surface receptor(s) for SP-A. In a previous report, we showed that the C-terminal non-collagen like domain of human SP-A possessed the biological activities, and that a monoclonal antibody against human SP-A, PE10, abolished the biological activity of SP-A (Murata et al. (1993) Biochem. J. 291, 71-76). In the present study, we investigated an epitope of SP-A for PE10. Western blot analysis with fragmented peptides of human SP-A generated by both lysyl endopeptidase and BrCN showed that PE10 reacted with the peptide corresponding with Glu202 to the C-terminal but that it lacked the ability to bind to the peptide corresponding with Tyr208 to the C-terminal. The antibodies against a synthetic peptide (P1) corresponding with Glu202 to Asn217 of human SP-A inhibited the binding of PE10 to SP-A, suggesting that a similar site was recognized by both PE10 and anti-P1 antibodies. Anti-P1 antibodies as well as PE10 suppressed the biological activity of SP-A. A direct interaction between P1 and rat lung membranes, or between P1 and alveolar type II cell membranes was shown from the measurement of the fluorescence emission spectra of dansyl-labeled P1. These results suggest that an area contiguous to or near the region from Glu202 to Met207 of SP-A is important for expressing the biological activities.

A mechanism for posttranslational modifications of proteins by yeast protein farnesyltransferase

Protein farnesyltransferase catalyzes the alkylation of cysteine in C-terminal CaaX sequences of a variety of proteins, including Ras, nuclear lamins, large G proteins, and phosphodiesterases, by farnesyl diphosphate (FPP). These modifications enhance the ability of the proteins to associate with membranes and are essential for their respective functions. The enzyme-catalyzed reaction was studied by using a series of substrate analogs for FPP to distinguish between electrophilic and nucleophilic mechanisms for prenyl transfer. FPP analogs containing hydrogen, fluoromethyl, and trifluoromethyl substituents in place of the methyl at carbon 3 were evaluated as alternative substrates for alkylation of the sulfhydryl moiety in the peptide dansyl-GCVIA. The analogs were alternative substrates for the prenylation reaction and were competitive inhibitors against FPP. A comparison of kcat for FPP and the analogs with ksolv, the rate constants for solvolysis of related p-methoxybenzenesulfonate derivatives, indicated that protein prenylation occurred by an electrophilic mechanism.

Interactions of the EcoRV restriction endonuclease with fluorescent oligodeoxynucleotides

A self-complementary dodecadeoxyribonucleotide that contains the recognition sequence for the R.EcoRV ENase was synthesised with a primary amino group at its 5' terminus. The 5' amino function was labeled with the fluorescent dye 5-[dimethylamino] napthalene-1-sulfonyl chloride. The labeled oligodeoxyribonucleotide in its duplex form was shown to be a suitable substrate for kinetic studies on the ENase and that no significant dye-DNA or dye-protein interactions occurred. Finally, the binding of R.EcoRV to the labeled DNA was followed by detecting the fluorescence resonance energy transfer between the tryptophans of the protein and the fluorescent labels of the DNA.

Assessment of aldehyde dehydrogenase in viable cells

Cytosolic aldehyde dehydrogenase (ALDH), an enzyme responsible for oxidizing intracellular aldehydes, has an important role in ethanol, vitamin A, and cyclophosphamide metabolism. High expression of this enzyme in primitive stem cells from multiple tissues, including bone marrow and intestine, appears to be an important mechanism by which these cells are resistant to cyclophosphamide. However, although hematopoietic stem cells (HSC) express high levels of cytosolic ALDH, isolating viable HSC by their ALDH expression has not been possible because ALDH is an intracellular protein. We found that a fluorescent aldehyde, dansyl aminoacetaldehyde (DAAA), could be used in flow cytometry experiments to isolate viable mouse and human cells based on their ALDH content. The level of dansyl fluorescence exhibited by cells after incubation with DAAA paralleled cytosolic ALDH levels determined by Western blotting and the sensitivity of the cells to cyclophosphamide. Moreover, DAAA appeared to be a more sensitive means of assessing cytosolic ALDH levels than Western blotting. Bone marrow progenitors treated with DAAA proliferated normally. Furthermore, marrow cells expressing high levels of dansyl fluorescence after incubation with DAAA were enriched for hematopoietic progenitors. The ability to isolate viable cells that express high levels of cytosolic ALDH could be an important component of methodology for identifying and purifying HSC and for studying cyclophosphamide-resistant tumor cell populations.

Nature of the masking of nucleotide-binding sites in brown adipose tissue mitochondria. Involvement of endogenous adenosine triphosphate

Binding of the fluorescent nucleotide derivative 2'-O-dansyl GTP and purine nucleotides to brown adipose tissue mitochondria from hamster was studied. 2'-O-Dansyl GTP binds with enhanced fluorescence to the uncoupling protein (UCP) in the mitochondria, similar to the isolated protein. The fluorescence signal showed biphasic fast and slow increases. Treatment of the mitochondria with an anion exchanger (Dowex) increased the total fluorescence but decreased the slower phase. The biphasic fluorescence response was restored by incubation with only 1 microM ATP, indicating that residual bound ATP may be responsible for the observed slow phase. The binding of [14C]GTP and GDP also increased after Dowex treatment. The dissociation of bound [14C]ATP but not of bound [14C]ADP was slow and apparently limited the binding assays. Short incubation (5 min) resulted in a curvature of the Scatchard plot, where the 'high-affinity sites' correspond to the free UCP sites; GDP had apparently higher affinity than GTP. Dowex treatment and incubation for 60 min produced a more linear Scatchard plot. Under such conditions, one measures the maximal UCP-binding sites (1.2 mumol/g protein); GTP exhibited higher affinity (Kd = 0.64 microM) than GDP (Kd = 3.1 microM). Acute cold adaptation (40 min at 4 degrees C) of hamsters caused an increase by over 40% of [14C]GTP binding, as compared to the control warm-(28 degrees C)-adapted animals. Dowex treatment completely abolishes this unmasking/masking effect, where both mitochondria had identical binding capacity and affinity for GTP. The inhibition by purine nucleotides of H+ transport as measured by potassium-acetate-induced mitochondrial swelling was dependent on the incubation time. Diphosphates inhibited faster and triphosphates required longer incubation (10 min) but inhibited more strongly. A linear correlation between the mitochondrial swelling rate and GDP binding was observed for mitochondria with depleted endogenous ATP or with added ATP. These data indicate that residual bound ATP from the tissue is responsible for the masking phenomenon.

Reactivity of histidyl residues in D-amino acid oxidase from Rhodotorula gracilis

Incubation of D-amino acid oxidase from the yeast Rhodotorula gracilis with excess dansyl chloride at pH 6.6 and 18 degrees C caused an irreversible inactivation of D-amino acid oxidase. Benzoate, a competitive inhibitor of the enzyme, completely protected the enzyme from inactivation. The dansylated-enzyme, isolated by gel-filtration, was in part still active while the substrate specificity was altered substantially. It was completely reduced by D-alanine in anaerobiosic conditions and did stabilize the red anion semiquinone upon photochemical reduction with EDTA. The results provide evidence for the presence of essential histidyl residue(s) in the active center of the yeast enzyme.

Structure and function of several anti-dansyl chimeric antibodies formed by domain interchanges between human IgM and mouse IgG2b

Two pairs of chimeric, domain-switched immunoglobulins with identical murine, anti-dansyl (5-dimethylaminonaphthalene-1-sulfonyl) variable domains have been generated, employing as parent antibodies a human IgM and a mouse IgG2b. The first pair of chimeric antibodies mu mu gamma mu and gamma gamma mu gamma was generated by switching the C mu 3 and C gamma 2 domains between IgM and IgG2b. The second pair of chimeras mu mu gamma gamma and gamma gamma mu mu were formed by switching both C mu 3 and C mu 4 with C gamma 2 and C gamma 3. SDS-polyacrylamide gel electrophoresis and analytical ultracentrifugation showed that over half (57 and 71%) of the two chimeric antibodies possessing the C mu 4 domain and tail piece formed disulfide-linked IgM-like polymers. In contrast, the two chimeric antibodies lacking the C mu 4 domain were almost entirely monomeric. Both monomeric chimeras had reduced ability to activate complement. The chimera gamma gamma mu gamma had no activity under any of the assay conditions, whereas mu mu gamma gamma caused only a small amount of cell lysis but was fully active in consuming complement at 4 degrees C. The polymeric chimera gamma gamma mu mu was much less active than IgM, bound C1 weakly and caused some cell lysis but consumed little complement with soluble antigen. The polymeric chimera mu mu gamma mu bound C1 strongly and was the most active antibody in all assays, even more active than the parental IgG2b and IgM antibodies; it was the only antibody that exhibited antigen-independent activity. The results suggest that C mu 3 alone does not constitute the complement binding site in IgM but requires both C mu 1-2 and C mu 4 for full activity.

Comparative thermodynamic analyses of the Fv, Fab* and Fab fragments of anti-dansyl mouse monoclonal antibody

In order to investigate the role of the constant domains on the antigen-binding property of the variable domains, we have carried out a comparative thermodynamic study of the anti-dansyl Fv, Fab* and Fab fragments that possess the identical amino acid sequence of the variable domains. The thermodynamic analyses have shown that binding constants, enthalpy changes and entropy changes are similar for the three antigen-binding fragments, whereas the thermal stability of Fab is much higher than that of Fv and Fab*. We have concluded that (i) the variable domains of the three antigen-binding fragments possess identical intrinsic capability for antigen binding and (ii) the two constant domains serve to improve the stability of the variable domains.

Fluorescent staining for proteins on polyacrylamide gels with 5-dimethylamino-1-naphthalenesulfonyl chloride (dansyl chloride)

A simple and sensitive post electrophoresis fluorescent staining technique for proteins on polyacrylamide gels using 5-dimethylamino-1-naphthalene sulfonyl chloride (dansyl chloride) has been developed. Dansyl chloride staining increases the sensitivity, 0.125 micrograms protein per band can be visualised by this technique. The staining method appears to be applicable to all types of proteins including proteoglycans.

Apolipoprotein E self-association in solution studied by non-radiative energy transfer

The self-association of human apolipoprotein E (apoE), isolated from plasma very low density lipoproteins, was studied at apoE concentrations less than 0.6 microM by non-radiative energy transfer. ApoE was separately labeled with a fluorescent donor group i.e. dansyl chloride (apoE/D) and with an acceptor i.e. fluorescein isothiocyanate (apoE/F). Mixed apoE/D:apoE/F complexes were prepared either by incubation or the donor- and of the acceptor-labeled apoE or by renaturation during dialysis of the apoE/D:apoE/F mixture pre-denatured by addition of guanidine hydrochloride or by treatment with sodium cholate. The efficiency of energy transfer E at an equimolar ratio of the donor to acceptor and a ratio of 1.9 mol fluorescein/mol protein amounted to 29.2 +/- 2.6% (n = 3). The E value increased linearly with increasing acceptor fraction in the mixture. The state of self-association of apoE as tetramers within this concentration range was confirmed by cross-linking experiments with a water-soluble bifunctional reagent. This approach can be applied to the study of protein-protein interactions in apolipoprotein-phospholipid recombinants.