Specific amyloid β clearance by a catalytic antibody construct

Classical immunization methods do not generate catalytic antibodies (catabodies), but recent findings suggest that the innate antibody repertoire is a rich catabody source. We describe the specificity and amyloid β (Aβ)-clearing effect of a catabody construct engineered from innate immunity principles. The catabody recognized the Aβ C terminus noncovalently and hydrolyzed Aβ rapidly, with no reactivity to the Aβ precursor protein, transthyretin amyloid aggregates, or irrelevant proteins containing the catabody-sensitive Aβ dipeptide unit. The catabody dissolved preformed Aβ aggregates and inhibited Aβ aggregation more potently than an Aβ-binding IgG. Intravenous catabody treatment reduced brain Aβ deposits in a mouse Alzheimer disease model without inducing microgliosis or microhemorrhages. Specific Aβ hydrolysis appears to be an innate immune function that could be applied for therapeutic Aβ removal.

Physiological IgM class catalytic antibodies selective for transthyretin amyloid

Peptide bond-hydrolyzing catalytic antibodies (catabodies) could degrade toxic proteins, but acquired immunity principles have not provided evidence for beneficial catabodies. Transthyretin (TTR) forms misfolded β-sheet aggregates responsible for age-associated amyloidosis. We describe nucleophilic catabodies from healthy humans without amyloidosis that degraded misfolded TTR (misTTR) without reactivity to the physiological tetrameric TTR (phyTTR). IgM class B cell receptors specifically recognized the electrophilic analog of misTTR but not phyTTR. IgM but not IgG class antibodies hydrolyzed the particulate and soluble misTTR species. No misTTR-IgM binding was detected. The IgMs accounted for essentially all of the misTTR hydrolytic activity of unfractionated human serum. The IgMs did not degrade non-amyloidogenic, non-superantigenic proteins. Individual monoclonal IgMs (mIgMs) expressed variable misTTR hydrolytic rates and differing oligoreactivity directed to amyloid β peptide and microbial superantigen proteins. A subset of the mIgMs was monoreactive for misTTR. Excess misTTR was dissolved by a hydrolytic mIgM. The studies reveal a novel antibody property, the innate ability of IgMs to selectively degrade and dissolve toxic misTTR species as a first line immune function.

Metal-dependent amyloid β-degrading catalytic antibody construct

Catalytic antibodies (catabodies) that degrade target antigens rapidly are rare. We describe the metal-dependence of catabody construct 2E6, an engineered heterodimer of immunoglobulin light chain variable domains that hydrolyzes amyloid β peptides (Aβ) specifically. In addition to the electrophilic phosphonate inhibitor of serine proteases, the metal chelators ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline completely inhibited the hydrolysis of Aβ by catabody 2E6. Formation of catabody-electrophilic phosphonate inhibitor adducts was unaffected by EDTA, suggesting that the metal exerts a favorable effect on a catalytic step after the initial catabody nucleophilic attack on Aβ. The EDTA inactivated catabody failed to disaggregate fibrillar Aβ, indicating the functional importance of the Aβ hydrolytic activity. Treating the EDTA-inactivated catabody with Zn(2+) or Co(2+) restored the Aβ hydrolytic activity, and Zn(2+)-induced catabody conformational transitions were evident by fluorescence emission spectroscopy. The studies reveal the absolute catabody dependence on a metal cofactor.

Antibodies to a superantigenic glycoprotein 120 epitope as the basis for developing an HIV vaccine

Failure to induce synthesis of neutralizing Abs to the CD4 binding determinant (CD4BD) of gp120, a central objective in HIV vaccine research, has been alternately ascribed to insufficient immunogen binding to Abs in their germline V region configuration expressed as BCRs, insufficient adaptive mutations in Ab V regions, and conformational instability of gp120. We employed peptide analogs of gp120 residues 421-433 within the CD4BD (CD4BD(core)) to identify Abs produced without prior exposure to HIV (constitutive Abs). The CD4BD(core) peptide was recognized by single-chain Fv fragments from noninfected humans with lupus that neutralized genetically diverse strains belonging to various HIV subtypes. Replacing the framework region (FR) of a V(H)4-family single-chain Fv with the corresponding V(H)3-family FRs from single-chain Fv JL427 improved the CD4BD(core) peptide-binding activity, suggesting a CD4BD(core) binding site outside the pocket formed by the CDRs. Replacement mutations in the FR site vicinity suggested the potential for adaptive improvement. A very small subset of serum CD4BD(core)-specific serum IgAs from noninfected humans without autoimmune disease isolated by epitope-specific chromatography neutralized the virus potently. A CD4BD(core)-specific, HIV neutralizing murine IgM with H and L chain V regions (V(H) and V(L) regions) free of immunogen-driven somatic mutations was induced by immunization with a CD4BD(core) peptide analog containing an electrophilic group that binds B cells covalently. The studies indicate broad and potent HIV neutralization by constitutive Abs as an innate, germline-encoded activity directed to the superantigenic CD4BD(core) epitope that is available for amplification for vaccination against HIV.

Constant domain-regulated antibody catalysis

Some antibodies contain variable (V) domain catalytic sites. We report the superior amide and peptide bond-hydrolyzing activity of the same heavy and light chain V domains expressed in the IgM constant domain scaffold compared with the IgG scaffold. The superior catalytic activity of recombinant IgM was evident using two substrates, a small model peptide that is hydrolyzed without involvement of high affinity epitope binding, and HIV gp120, which is recognized specifically by noncovalent means prior to the hydrolytic reaction. The catalytic activity was inhibited by an electrophilic phosphonate diester, consistent with a nucleophilic catalytic mechanism. All 13 monoclonal IgMs tested displayed robust hydrolytic activities varying over a 91-fold range, consistent with expression of the catalytic functions at distinct levels by different V domains. The catalytic activity of polyclonal IgM was superior to polyclonal IgG from the same sera, indicating that on average IgMs express the catalytic function at levels greater than IgGs. The findings indicate a favorable effect of the remote IgM constant domain scaffold on the integrity of the V-domain catalytic site and provide a structural basis for conceiving antibody catalysis as a first line immune function expressed at high levels prior to development of mature IgG class antibodies.

Toward effective HIV vaccination: induction of binary epitope reactive antibodies with broad HIV neutralizing activity

We describe murine monoclonal antibodies (mAbs) raised by immunization with an electrophilic gp120 analog (E-gp120) expressing the rare ability to neutralize genetically heterologous human immunodeficiency virus (HIV) strains. Unlike gp120, E-gp120 formed covalent oligomers. The reactivity of gp120 and E-gp120 with mAbs to reference neutralizing epitopes was markedly different, indicating their divergent structures. Epitope mapping with synthetic peptides and electrophilic peptide analogs indicated binary recognition of two distinct gp120 regions by anti-E-gp120 mAbs, the 421-433 and 288-306 peptide regions. Univalent Fab and single chain Fv fragments expressed the ability to recognize both peptides. X-ray crystallography of an anti-E-gp120 Fab fragment revealed two neighboring cavities, the typical antigen-binding cavity formed by the complementarity determining regions (CDRs) and another cavity dominated by antibody heavy chain variable (V(H)) domain framework (FR) residues. Substitution of the FR cavity V(H) Lys-19 residue by an Ala residue resulted in attenuated binding of the 421-433 region peptide probe. The CDRs and V(H) FR replacement/silent mutation ratios exceeded the ratio for a random mutation process, suggesting adaptive development of both putative binding sites. All mAbs studied were derived from V(H)1 family genes, suggesting biased recruitment of the V gene germ line repertoire by E-gp120. The conserved 421-433 region of gp120 is essential for HIV binding to host CD4 receptors. This region is recognized weakly by the FR of antibodies produced without exposure to HIV, but it usually fails to induce adaptive synthesis of neutralizing antibodies. We present models accounting for improved CD4-binding site recognition and broad HIV neutralizing activity of the mAbs, long sought goals in HIV vaccine development.

Characterization of gp120 hydrolysis by IgA antibodies from humans without HIV infection

Antibody hydrolysis of the superantigenic gp120 site and HIV-1 neutralization was studied as a potential anti-HIV mechanism in uninfected humans. gp120 hydrolysis by purified serum and salivary antibodies was determined by electrophoresis and peptide sequencing, the proteolytic mechanism was analyzed using electrophilic peptide analogs, and viral neutralization was studied using peripheral blood mononuclear cells as hosts. Polyclonal and monoclonal IgA but not IgG preparations selectively catalyzed the cleavage of HIV gp120 at rates sufficient to predict biologically relevant protection against the virus. The IgA hydrolytic reaction proceeded by noncovalent recognition of gp120 residues 421-433, a component of the superantigenic site of gp120, coordinated with peptide bond cleavage via a serine protease-like mechanism. The Lys-432-Ala-433 bond was one of the cleavage sites. Infection of peripheral blood mononuclear cells by a primary isolate of HIV was neutralized by the IgA but not IgG fractions. The neutralizing activity was specifically inhibited by an electrophilic inhibitor of the catalytic activity. The existence of catalytic IgAs to gp120 in uninfected humans suggests their role in resistance to HIV.

Naturally occurring catalytic antibodies: evidence for preferred development of the catalytic function in IgA class antibodies

IgG class antibodies express catalytic activities rarely and at very low levels. Here, we studied polyclonal IgA and IgG preparations from healthy human sera and saliva for the ability to hydrolyze model peptidyl-aminomethylcoumarin (peptide-AMC) substrates. These substrates permit objective evaluation of the catalytic potential of the antibody classes with minimal effects of noncovalent interactions occurring at sites remote from the reaction center. The IgA preparations hydrolyzed Glu-Ala-Arg-AMC at rates 3-orders of magnitude greater than IgG preparations from the same individuals. The cleavage occurred preferentially on the C terminal side of a basic residue. The activity was confirmed using monoclonal IgAs isolated from patients with multiple myeloma. Active site-directed inhibitors of serine proteases inhibited the catalytic activity and were bound irreversibly by the IgA, suggesting the involvement of a serine protease-like mechanism similar to that utilized by previously described IgM antibodies. These observations suggest that mechanisms underlying B cell clonal selection favor the retention and improvement of catalytic activity in the IgA, but not the IgG compartment of the immune response.

Towards Covalent Vaccination

Rare monoclonal antibodies (Abs) can form irreversible complexes with antigens by enzyme-like covalent nucleophile-electrophile pairing. To determine the feasibility of applying irreversible antigen inactivation by Abs as the basis of vaccination against microbes, we studied the polyclonal nucleophilic Ab response induced by the electrophilic analog of a synthetic peptide corresponding to the principal neutralizing determinant (PND) of human immunodeficiency virus type-1 (HIV) gp120 located in the V3 domain. Abs from mice immunized with the PND analog containing electrophilic phosphonates (E-PND) neutralized a homologous HIV strain (MN) approximately 50-fold more potently than control Abs from mice immunized with PND. The IgG fractions displayed binding to intact HIV particles. HIV complexes formed by anti-E-PND IgG dissociated noticeably more slowly than the complexes formed by anti-PND IgG. The slower dissociation kinetics are predicted to maintain long-lasting blockade of host cell receptor recognition by gp120. Pretreatment of the anti-PND IgG with a haptenic electrophilic phosphonate compound resulted in more rapid dissociation of the HIV-IgG complexes, consistent with the hypothesis that enhanced Ab nucleophilic reactivity induced by electrophilic immunization imparts irreversible character to the complexes. These results suggest that electrophilic immunization induces a sufficiently robust nucleophilic Ab response to enhance the anti-microbial efficacy of candidate polypeptide vaccines.

Towards site-directed covalent vaccination: HIV neutralization by antibodies to an electrophilic gp120 V3 peptide (47.38)

We observed recently that antibodies (Abs) to an analog of full-length HIV gp120 analog containing electrophilic phosphonate groups located at Lys (E-gp120) form stable immune complexes characterized by very slow dissociation and resistance to denaturants. We hypothesize that the unusual stability is due to the partial covalent character of the complexes, mediated by enhanced Ab nucleophilic reactivity developing in response to electrophilic immunization. Here we tested the feasibility of inducing an epitope-specific nucleophilic Ab response on-demand using as immunogen the electrophilic analog of the principal neutralizing determinant of HIV gp120 (E-PND). Murine IgG Abs raised to E-PND and non-electrophilic PND displayed binding to intact HIV particles. Complexes of HIV with anti-E-PND IgG dissociated ~25-times slower than the complexes with anti-PND IgG. Anti-E-PND IgG neutralized HIV more potently than anti-PND IgG, determined using a T cell line assay (difference in IC50, ~50-fold). The slower dissociation kinetics can be expected to maintain long-lasting blockade of gp120 recognition by host receptors, resulting in superior HIV neutralization. These results suggest the utility of electrophilic immunization to enhance the protective efficacy of site-specific humoral immunity against peptide antigens.

Adaptive development of catalytic antibodies to the gp120 superantigenic site in lupus and HIV infected patients (44.43)

The B cell superantigenic site of the HIV protein gp120 (gp120SAg) is important in viral entry into host cells and gp120SAg binding IgG in the preimmune repertoire reduce the risk of infection. Like the gp120SAg binding function, the innate catalytic function of antibody (Ab) variable domains is subject to deterioration during B cell maturation, and gp120SAg binding Abs are not produced appreciably following infection. We report the selection of catalytic single chain Fv (scFv) and light chain (L chain) clones from the Ab repertoire of patients with lupus, a condition involving increased production of gp120SAg binding Abs. The Ab fragments were isolated by covalent phage selection using electrophilic gp120 analogs. Several selected fragments cleaved gp120 via a nucleophilic mechanism coordinated with noncovalent recognition of gp120(421–433), determined by electrophoretic assays. Certain clones neutralized HIV infection in cultured peripheral blood mononuclear cells (low μg/ml potency), including two scFv clones that neutralized primary clade B, C and D strains. In contrast to lupus patients, studies on polyclonal IgG and IgA from HIV infected patients did not support the presence of an amplified Ab response to gp120SAg. IgAs from a minority of infected subjects with no progression to AIDS 5.5 years following seroconversion displayed increased gp120 hydrolysis compared to rapid progressors (P<0.0001). These data suggest catalytic Abs as a protective anti-viral mechanism and open the way to considerations of immunogens that stimulate catalytic immunity as candidate vaccines.

Towards irreversible HIV inactivation: stable gp120 binding by nucleophilic antibodies

Conventional antibodies react with antigens reversibly. We report the formation of unusually stable complexes of HIV gp120 and nucleophilic antibodies raised by immunization with an electrophilic HIV gp120 analog (E-gp120). The stability of the complexes was evident from their very slow dissociation in a nondenaturing solvent (approximate t(1/2) 18.5 days) and their resistance to dissociation by a denaturant commonly employed to disrupt noncovalent protein-protein binding (sodium dodecyl sulfate). Kinetic studies indicated time-dependent and virtually complete progression of the antibody-gp120 complexes from the initial noncovalent state to a poorly dissociable state. The antibodies to E-gp120 displayed improved covalent reactivity with an electrophilic phosphonate probe compared to control antibodies, suggesting their enhanced nucleophilicity. One of the stably binding antibodies neutralized the infectivity of CCR5-dependent primary HIV strains belonging to clades B and C. These findings suggest the feasibility of raising antibodies capable of long-lasting inactivation of antigens by electrophilic immunization.

Investigation of active form of catalytic antibody light chain 41S-2-L

We have raised a monoclonal antibody (41S-2) against the conserved sequence, RGPDRPEGIEEEGGERDRD, of human immunodeficiency virus type1 (HIV-1) envelope gp41. That antibody light chain (41S-2-L) cleaves gp41-derived peptide (TPRGPDRPEGIEEEGGERDRD; TP41-1) with a characteristic biphasic profile composed of induction and active phases. It is considered that the conformation of 41S-2-L is changed, by such as induced fitting, to move to active phase to decompose the antigenic peptide during the induction phase. In order to investigate what happens to 41S-2-L in the induction and active phase, the cleavage reaction of the peptide by 41S-2-L was examined in detail from the viewpoint of kinetic and spectroscopic analysis. The kinetic data showed that the preferable conformational transition of 41S-2-L took place by the unimolecular reaction of 41S-2-L in the induction phase. UV-vis and fluorescence spectroscopic analysis suggested that the conformational transition leads to the generation of aggregates of 41S-2-L in the reacting solution, which causes the huge enhancement of the catalytic activity of 41S-2-L. The nuclei of the aggregates may be formed in the induction phase. The aggregates and soluble 41S-2-L are considered to be in chemical equilibrium during the cleavage reaction of the antigen.

Broadly distributed nucleophilic reactivity of proteins coordinated with specific ligand binding activity

Covalent nucleophile-electrophile interactions have been established to be important for recognition of substrates by several enzymes. Here, we employed an electrophilic amidino phosphonate ester (EP1) to study the nucleophilic reactivity of the following proteins: albumin, soluble epidermal growth factor receptor (sEGFR), soluble CD4 (sCD4), calmodulin, casein, alpha-lactalbumin, ovalbumin, soybean trypsin inhibitor and HIV-1 gp120. Except for soybean trypsin inhibitor and alpha-lactalbumin, these proteins formed adducts with EP1 that were not dissociated by denaturing treatments. Despite their negligible proteolytic activity, gp120, sEGFR and albumin reacted irreversibly with EP1 at rates comparable to the serine protease trypsin. The neutral counterpart of EP1 reacted marginally with the proteins, indicating the requirement for a positive charge close to the electrophilic group. Prior heating resulted in altered rates of formation of the EP1-protein adducts accompanied by discrete changes in the fluorescence emission spectra of the proteins, suggesting that the three-dimensional protein structure governs the nucleophilic reactivity. sCD4 and vasoactive intestinal peptide (VIP) containing phosphonate groups (EP3 and EP4, respectively) reacted with their cognate high-affinity binding proteins gp120 and calmodulin, respectively, at rates exceeding the corresponding reactions with EP1. Reduced formation of EP3-gp120 adducts and EP4-calmodulin adducts in the presence of sCD4 and VIP devoid of the phosphonate groups was evident, suggesting that the nucleophilic reactivity is expressed in coordination with non-covalent recognition of peptide determinants. These observations suggest the potential of EPs for specific and covalent targeting of proteins, and raise the possibility of nucleophile-electrophile pairing as a novel mechanism stabilizing protein-protein complexes.

Catalytic antibody light chain capable of cleaving a chemokine receptor CCR-5 peptide with a high reaction rate constant

A monoclonal antibody (MAb), ECL2B-2, was obtained by immunizing a peptide possessing a part of a sequence of a chemokine receptor, CCR-5, which is present as a membrane protein on the macrophage surface, and which plays an important role in human immunodeficiency virus (HIV) infection. From the DNA and the deduced amino acid sequences of the light and heavy chains of ECL2B-2 MAb, molecular modeling was conducted to calculate the steric conformation of the antibody. Modeling suggested that the structure of ECL2B-2 could possess one or two catalytic triad(s), composed of Asp(1), Ser(27a) (or Ser(27e)), and His(93) (or His(27d)), in the light chain of ECL2B-2. The three amino acid residues, Asp(1), Ser(27a), and His(93), are identical to those of catalytic antibody light chains such as VIPase and i41SL1-2. The light chain of ECL2B-2 MAb degraded the antigenic peptide CCR-5 within about 100 h. Surprisingly, the light chain had a very high catalytic reaction rate constant (k(cat)) of 2.23 min(-1), which is greater by factors of tens to hundreds than those of natural catalytic antibodies obtained previously. The heavy chain of ECL2B-2 MAb, which has no catalytic triad because of a lack of His residue, did not degrade the CCR-5 peptide.

Catalytic features of monoclonal antibody i41SL1-2 subunits

A monoclonal antibody (mAb), i41SL1-2, was obtained by immunizing the peptide of complementarity-determining region-1 (CDRL-1: RSSKSLLYSNGNTYLY) of a super catalytic antibody light chain, 41S-2-L, capable of enzymatically destroying the gp41 molecule of the HIV-1 envelope. From the DNA and the deduced amino acid sequences of the light and heavy chain of i41SL1-2 mAb, molecular modeling was conducted that suggested that both subunits of i41SL1-2 mAb possess catalytic triads in their structures. Especially the light chain of i41SL1-2 mAb possesses a characteristic catalytic triad composed of Asp(1), Ser(27A), and His(93), whose positions are identical to the catalytic antibody light chain, VIPase, of S. Paul and colleagues (see text). The antibody gene of i41SL1-2 light chain and VIPase belong to the same germline, bd2, suggesting that the discrete germline inherently possesses catalytic activity. Both light and heavy chains of i41SL1-2 mAb degraded the antigenic peptide CDRL-1 within 47 and 57 h, respectively. The catalytic reaction constant (kcat) of the light and heavy chain was 6.1 x 10(-1) and 6.2 x 10(-1) min(-1), respectively. These are high values for the natural catalytic antibodies reported so far. The catalytic efficiency (kcat/Km) of the light and heavy chain was 3.1 x 10(5) and 4.9 x 10(4) M(-1) min(-1), respectively. The first cleaved bond of the antigenic peptide by subunits of i41SL1-2 mAb was between Arg(1) and Ser(2) in the sequence of CDRL-1, suggesting a serine protease character.

Toward selective covalent inactivation of pathogenic antibodies: a phosphate diester analog of vasoactive intestinal peptide that inactivates catalytic autoantibodies

We report the selective inactivation of proteolytic antibodies (Abs) to an autoantigen, the neuropeptide vasoactive intestinal peptide (VIP), by a covalently reactive analog (CRA) of VIP containing an electrophilic phosphonate diester at the Lys(20) residue. The VIP-CRA was bound irreversibly by a monoclonal Ab that catalyzes the hydrolysis of VIP. The reaction with the VIP-CRA proceeded more rapidly than with a hapten CRA devoid of the VIP sequence. The covalent binding occurred preferentially at the light chain subunit of the Ab. Covalent VIP-CRA binding was inhibited by VIP devoid of the phosphonate diester group. These results indicate the importance of noncovalent VIP recognition in guiding Ab nucleophilic attack on the phosphonate group. Consistent with the covalent binding data, the VIP-CRA inhibited catalysis by the recombinant light chain of this Ab with potency greater than the hapten-CRA. Catalytic hydrolysis of VIP by a polyclonal VIPase autoantibody preparation that cleaves multiple peptide bonds located between residues 7 and 22 essentially was inhibited completely by the VIP-CRA, suggesting that the electrophilic phosphonate at Lys(20) enjoys sufficient conformational freedom to react covalently with Abs that cleave different peptide bonds in VIP. These results suggest a novel route to antigen-specific covalent targeting of pathogenic Abs.

Endopeptidase character of monoclonal antibody i41-7 subunits

We prepared six anti-idiotypic monoclonal antibodies (mAbs) against parent 41S-2 mAb whose light chain is a super catalytic antibody (41S-2-L) capable of degrading targeted HIV-1gp41 molecule. Out of the obtained six mAbs, i41-7 mAb showed the strongest affinity to the parent 41S-2 mAb. The three dimensional structure of i41-7 mAb was created by molecular modeling using the deduced amino acid sequence of the light and heavy chain of i41-7 mAb. It suggests that the light and heavy chain possess catalytic triad-like structure composed of Ser, His and Asp in their conformations. Both chains of i41-7 mAb could cleave peptide bond of some peptides such as a polypeptide, TP41-1 (TPRGPDRPEGIEEEGGERDRD), as anticipated. The cleaving reaction advanced in accordance with Michaelis-Menten equation. The catalytic efficiency (kcat/Km) of light and heavy chain was 9.1 x 10(3) and 1.7 x 10(4) M(-1) x min(-1), respectively, while the intact i41-7 mAb did not exhibit any catalytic activity. The first cleaved bond of the TP41-1 peptide by the light chain was between 14E and 15G in the sequence. It was revealed that both light and heavy chains had endopeptidase characteristics.

Targeted destruction of the HIV-1 coat protein gp41 by a catalytic antibody light chain

Generation of antibodies with the ability to destroy targeted viral coat proteins or tumor antigens is an important aim in current research aimed at developing superior catalytic antibodies. To this end, we raised a monoclonal antibody against a discrete sequence of the envelope gp41, RGPDRPEGIEEEGGERDRD, which is a highly conserved sequence in many human immunodeficiency virus (HIV)-1 strains. The light chain subunit of this antibody catalytically decomposed the targeted peptide antigen. The degradation of the immunized peptide antigen by the light chain was initiated by the hydrolytic scission of the peptide bond between Glu12-Gly13, followed by the successive cleavage reactions of the additional peptic bonds into small peptides and amino acids. The decomposition by the light chain obeyed Michaelis-Menten kinetics (k(cat)/K(m) = 2. 8 x 10(5) M(-1) min(-1)). A characteristic feature of the reaction was a slow initial degradation step, followed by an increase in the rate of catalysis. Removal of the light chain by immunoadsorption at either stage of the reaction resulted in recession of catalysis. The light chain also cleaved recombinant gp41 molecule, but did not degrade proteins unrelated in the sequence to the peptide immunogen (bovine and human serum albumins).

Inhibitory effects of Rooibos tea, Aspalathus linealis, on X-ray-induced C3H10T1/2 cell transformation

Oncogenic transformation of mouse C3H10T1/2 cells induced by X-rays was suppressed in the presence of extract of Rooibos tea, Aspalathus linealis. Transformation was reduced with increased concentration of the extract, so that at an extract concentration of 10%, transformation incidence was similar to the spontaneous level. Suppression was also dependent on treatment time with the extract and was maximal when present during the entire incubation period. In contrast, green tea extract at an equitoxic concentration showed no detectable effect on transformation incidence.

Alteration of specific activity and stability of thermostable neutral protease by site-directed mutagenesis

On the basis of three-dimensional information, many amino acid substitutions were introduced in the thermostable neutral protease (NprM) of Bacillus stearothermophilus MK232 by site-directed mutagenesis. When Glu at position 143 (Glu-143), which is one of the proposed active sites, was substituted for by Gln and Asp, the proteolytic activity disappeared. F114A (Phe-114 to Ala), Y110W (Tyr-110 to Trp), and Y211W (Tyr-211 to Trp) mutant enzymes had higher activity (1.3- to 1.6-fold) than the wild-type enzyme. When an autolysis site, Tyr-93, was replaced by Gly and Ser, the remaining activities of those mutant enzymes were higher than that of the wild-type enzyme.

Estimation of Long-Chain Branching in Ethylene-Propylene Terpolymers from Infinite-Dilution Viscoelastic Properties

A method is outlined for estimation of small degrees of long-chain branching in polymers with moderately narrow molecular weight distribution (Mw/Mn<1.4). The storage and loss shear moduli, G′ and G″, are measured in dilute solution by the Birnboim-Schrag multiple-lumped resonator and extrapolated to infinite dilution, choosing a suitable solvent viscosity and frequency range such that the data lie in the terminal zone where G′ and G″ are proportional to the second and first powers of frequency, respectively. The intrinsic reduced steady-state shear compliance is determined from these data and corrected for moderate molecular weight heterogeneity (assuming a Gaussian distribution) from knowledge ofMw/Mn and the Mark-Houwink exponent a. The resulting value of S2/S12 (where S1=∑ τp/τ1, S2=∑ (τp/τ1)2, the τp's being the relaxation times and τ1 the longest one) is compared with values calculated by the Zimm-Kilb theory as evaluated by Osaki for comb polymers of regular geometry and different numbers of branch points. The method has been illustrated by measurements on four ethylene-propylene copolymers. One containing no termonomer and one containing a saturated termonomer appeared to be linear; two containing unsaturated termonomers showed small degrees of branching. The method appears to be promising for detecting from one to four branch points per molecule.