Prospects for a better vaccine against tuberculosis

There have been many new promising approaches to developing human vaccines against tuberculosis (TB). Advances in gene and antigen identification, availability of genome sequences, a greater understanding of immune mechanisms in resistance to TB, the development of adjuvants and delivery systems to stimulate T-cell immunity, and increased funding from public and private agencies are some of the reasons for progress in this area. Dozens of vaccine candidates have been tested in animal models in recent years, and several of these are poised to move into clinical trials in the next several years. Thus, there is renewed optimism for the potential of developing new and improved TB vaccines.

Expression, refolding and crystallization of the OpcA invasin from Neisseria meningitidis

OpcA is an integral outer membrane from the Gram-negative pathogen Neisseria meningitidis that plays a role in adhesion of meningococci to host cells. The protein was overexpressed in Escherichia coli in an insoluble form and a procedure developed for refolding by rapid dilution from denaturant into detergent solution. The refolded material was identical to native OpcA isolated from meningococci, as judged by overall molecular weight, migration on SDS-PAGE and reaction against monoclonal antibodies. Both native and recombinant OpcA crystallized under similar conditions to give an orthorhombic crystal form (P2(1)2(1)2), with unit-cell parameters a = 96.9, b = 46.3, c = 74.0 A. Complete data sets of reflections were collected from native and refolded OpcA to 2.0 A resolution.

Inhibition of Borrelia burgdorferi-tick interactions in vivo by outer surface protein A antibody

Borrelia burgdorferi outer surface protein (Osp) A is preferentially expressed by spirochetes in the Ixodes scapularis gut and facilitates pathogen-vector adherence in vitro. Here we examined B. burgdorferi-tick interactions in vivo by using Abs directed against OspA from each of the three major B. burgdorferi sensu lato genospecies: B. burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii. Abs directed against B. burgdorferi sensu stricto (isolate N40) destroy the spirochete and can protect mice from infection. In contrast, antisera raised against OspA from B. afzelii (isolate ACA-1) and B. garinii (isolate ZQ-1) bind to B. burgdorferi N40 but are not borreliacidal against the N40 isolate. Our present studies assess whether these selected OspA Abs interfere with B. burgdorferi-tick attachment in a murine model of Lyme disease with I. scapularis. We examined engorged ticks that had fed on B. burgdorferi N40-infected scid mice previously treated with OspA (N40, ACA-1, ZQ-1, or mAb C3.78) or control Abs. OspA-N40 antisera or mAb C3.78 destroyed B. burgdorferi N40 within the engorged ticks. In contrast, treatment of mice with OspA-ACA-1 and OspA-ZQ-1 antisera did not kill B. burgdorferi N40 within the ticks but did effectively interfere with B. burgdorferi-I. scapularis adherence, thereby preventing efficient colonization of the vector. These studies show that nonborreliacidal OspA Abs can inhibit B. burgdorferi attachment to the tick gut, highlighting the importance of OspA in spirochete-arthropod interactions in vivo.

Transmission of Borrelia garinii OspA serotype 4 to BALB/c mice by Ixodes ricinus ticks collected in the field

In Europe, Borrelia garinii OspA serotype 4 has been isolated from the cerebrospinal fluid of patients but, up to now, has never been identified among culture isolates from Ixodes ricinus ticks. This information raises the question of whether OspA serotype 4 is transmitted by I. ricinus in nature. In the present study, I. ricinus nymphs collected in an area of endemicity in southern Germany were allowed to feed on mice. Cultivation of ear biopsy specimens showed that six of seven B. garinii-infected mice were infected by OspA serotype 4. In contrast, very few B. garinii OspA serotype 4 organisms were isolated directly from the ticks which infected the mice; most isolates were B. afzelii. The infected mice transmitted mainly OspA serotype 4 to xenodiagnostic ticks, preferentially in combination with B. afzelii.

Developing a nontypeable Haemophilus influenzae (NTHi) vaccine

There is a current high demand for nontypable Haemophilus influenzae (NTHi) vaccines. Various options for the composition of such vaccines are possible. Decisions about the vaccine composition have to take into account the antigenic variability of NTHi, so even complex immunogens such as whole bacteria would preferentially have a tailor-made antigenic composition. We will present a summary of NTHi vaccine development, describing research efforts from SmithKline Beecham and other laboratories. Currently, major (P1, P2, P4, P5) and minor (P6, D15, TbpA/B, ellipsis) outer membrane proteins, LPS, adhesins (HMW, Hia, pili, P5) are being studied. Preclinical results with LPD, P5 (LB1) and OMP26 from our laboratories will be described including the use of animal models of otitis and lung infection.

Attachment of Borrelia burgdorferi within Ixodes scapularis mediated by outer surface protein A

Borrelia burgdorferi outer surface protein (Osp) A has been used as a Lyme disease vaccine that blocks transmission: OspA antibodies of immune hosts enter ticks during blood feeding and destroy spirochetes before transmission to the host can occur. B. burgdorferi produce OspA in the gut of unfed Ixodes scapularis ticks, and many spirochetes repress OspA production during the feeding process. This preferential expression suggests that OspA may have an important function in the vector. Here we show that OspA mediates spirochete attachment to the tick gut by binding to an I. scapularis protein. The binding domains reside in the central region and COOH-terminus of OspA. OspA also binds to itself, suggesting that spirochete-spirochete interactions may further facilitate adherence in the gut. OspA-mediated attachment in the tick provides a possible mechanism for how stage-specific protein expression can contribute to pathogenesis during the B. burgdorferi natural cycle.

Passive transfer of antiserum specific for immunogens derived from a nontypeable Haemophilus influenzae adhesin and lipoprotein D prevents otitis media after heterologous challenge

We recently determined that passive transfer of serum directed against a synthetic peptide called LB1 or a recombinant fusion protein immunogen [LPD-LB1(f)(2,1,3)] could prevent otitis media after challenge with a homologous nontypeable Haemophilus influenzae (NTHI) isolate. NTHI residing in the nasopharynx was rapidly cleared from this site, thus preventing it from ascending the eustachian tube and inducing otitis media in chinchillas compromised by an ongoing viral upper respiratory tract infection. While LB1 is based solely on one NTHI adhesin, the latter immunogen, LPD-LB1(f)(2,1,3), was designed to incorporate two NTHI antigens shown to play a role in the pathogenesis of otitis media; lipoprotein D (LPD) and the P5-homologous fimbrin adhesin. The design of LPD-LB1(f)(2,1,3) also accommodated for the recently demonstrated existence of three major groupings, based on amino acid sequence diversity, in the third surface-exposed region of P5-fimbrin. LPD-LB1(f)(2,1,3) was thus designed to potentially confer broader protection against challenge by diverse strains of NTHI. Chinchillas were passively immunized here with serum specific for either LB1 or for LPD-LB1(f)(2,1,3) prior to challenge with a member of all three groups of NTHI relative to diversity in region 3. The transferred serum pools were also analyzed for titer, specificity, and several functional activities. We found that both serum pools had equivalent ability to mediate C'-dependent killing and to inhibit adherence of NTHI strains to human oropharyngeal cells. When passively transferred, both serum pools significantly inhibited the signs and incidence of otitis media (P </= 0.01) induced by any of the three challenge isolates. Despite providing protection against disease, the ability of these antisera to induce total eradication of NTHI from the nasopharynx was not equivalent among NTHI groups. These data thus suggested that while early, complete eradication of NTHI from the nasopharynx was highly protective, reduction of the bacterial load to below a critical threshold level appeared to be similarly effective.

Protection against development of otitis media induced by nontypeable Haemophilus influenzae by both active and passive immunization in a chinchilla model of virus-bacterium superinfection

Three separate studies, two involving active-immunization regimens and one involving a passive-transfer protocol, were conducted to initially screen and ultimately more fully assess several nontypeable Haemophilus influenzae outer membrane proteins or their derivatives for their relative protective efficacy in chinchilla models of otitis media. Initial screening of these antigens (P5-fimbrin, lipoprotein D, and P6), delivered singly or in combination with either Freund's adjuvant or alum, indicated that augmented bacterial clearance from the nasopharynx, the middle ears, or both anatomical sites could be induced by parenteral immunization with P5-fimbrin combined with lipoprotein D, lipoprotein D alone, or the synthetic chimeric peptide LB1 (derived from P5-fimbrin), respectively. Data from a second study, wherein chinchillas were immunized with LB1 or lipoprotein D, each delivered with alum, again indicated that clearance of nontypeable H. influenzae could be augmented by immunization with either of these immunogens; however, when this adjuvant was used, both antibody titers in serum and efficacy were reduced. A third study was performed to investigate passive delivery of antisera directed against either LB1, lipoprotein D, nonacylated lipoprotein D, or a unique recombinant peptide designated LPD-LB1(f)2,1,3. The last three antiserum pools were generated by using the combined adjuvant of alum plus monophosphoryl lipid A. Passive transfer of sera specific for LB1 or LPD-LB1(f)2,1,3 to adenovirus-compromised chinchillas, prior to intranasal challenge with nontypeable H. influenzae, significantly reduced the severity of signs and incidence of otitis media which developed (P </= 0.001). Collectively, these data indicate the continued merit of further developing LB1 and LPD-LB1(f)2,1,3 as components of vaccines for otitis media.

The outer surface protein A (OspA) vaccine against Lyme disease: efficacy in the rhesus monkey

The efficacy of an outer surface protein A (OspA) vaccine in three different formulations was investigated in the rhesus monkey. The challenge infection was administered using Ixodes scapularis ticks that were infected with the B31 strain of Borrelia burgdorferi. Protection was assessed against both infection and disease, by a variety of procedures. Some of the animals were radically immune suppressed, as an attempt to reveal any putative low level infection in the vaccinated animals. The significant difference found between the spirochaetal infection rates of ticks that had fed on vaccinated vs. control monkeys, lack of seroconversion in the vaccinated animals, and the absence of spirochaetal DNA in the skin of vaccinated animals in the weeks following the challenge, indicate that vaccinated monkeys were protected against tick challenge. The post-mortem immunohistochemical and polymerase chain reaction analyses, however, suggest that these monkeys may have undergone a low-level infection that was transient.

Immunization with a polyvalent OspA vaccine protects mice against Ixodes ricinus tick bites infected by Borrelia burgdorferi ss, Borrelia garinii and Borrelia afzelii

Sequence variability of the outer surface protein (Osp) A among Borrelia burgdorferi sl species suggests that a monovalent OspA vaccine may not protect against the various Borrelia present in Eurasia. Here, we confirmed that a monovalent recombinant OspA (rOspA) vaccine does not protect mice against Ixodes ricinus mediated infection with B. burgdorferi ss, Borrelia garinii and Borrelia afzelii. However, when mice were vaccinated with a cocktail of various rOspA from these three species, they were protected, and all challenge ticks that fed on them were cleared of their spirochetes. These results showed that a multiple OspA antigens vaccine, compatible with human use, was very efficient at protecting mice against B. burgdorferi ss, B. garinii, and B. afzelii.

Reactivity with a specific epitope of outer surface protein A predicts protection from infection with the Lyme disease spirochete, Borrelia burgdorferi

The response to recombinant vaccines for Lyme disease was studied to determine serum antibody levels effective in protecting against tick-transmitted infection. Data presented here demonstrate a significant correlation between antibody to an epitope on outer surface protein A (OspA) and protection against infection with Borrelia burgdorferi in canines and mice. A competitive enzyme-linked immunosorbent assay was developed to measure antibody to a site on OspA, defined by monoclonal antibody LA-2. Comparison of LA-2 titers against infection of canines and mice following vaccination and challenge established a predicted value for LA-2 titers. The statistical relationship between serum antibody levels and protection was calculated by logistic regression analysis. The statistical model predicted that an LA-2 titer of 0.32 microg equivalents (eq) per ml correlated to an 80% predicted probability of protection for both mice and dogs. This value was used to classify mice and dogs as to their protected status at the time of tick exposure. The LA-2 cutoff titer (0.32 microg eq/ml) correctly classified all dogs (n = 13) and mice (n = 44) that failed to become infected. By contrast, 20 of 22 dogs and 28 of 31 mice with titers of less than 0.32 microg eq/ml became infected. On the basis of these results, we conclude that an LA-2 titer is a reliable indicator of immune status for estimating immune protection following use of OspA-based vaccines for B. burgdorferi sensu stricto.

Evaluation of the safety, reactogenicity and immunogenicity of three recombinant outer surface protein (OspA) lyme vaccines in healthy adults

The safety, reactogenicity and immunogenicity of three candidate Lyme vaccines based on recombinant outer surface protein (OspA) presented in either lipidated or unlipidated forms, were assessed in 300 seronegative volunteers. Subjects received three doses of one of the three formulations at monthly intervals and were evaluated for antibody levels and the presence of symptoms after each dose. All formulations proved to be safe, the majority of local reactions being reported as mild, and all general symptoms were perceived to be either-mild or moderate in intensity. No subject refused a subsequent vaccine dose. All subjects were tested for both anti-OspA IgG and LA-2 equivalent antibodies up until day 84. All three vaccines induced an immune response but subjects who received lipoprotein OspA had the highest anti-OspA IgG and LA-2 equivalent GMTs after each dose and this was also true for the subset of subjects tested on day 180. The lipoprotein OspA group also had the largest number of subjects who remained seropositive for anti-OspA IgG antibodies. As the lipoprotein formulation produced the strongest immune response, with symptoms which were acceptable to all the vaccinees, we suggest further development of this vaccine.

Efficacy of human Lyme disease vaccine formulations in a mouse model

Although immunization with recombinant outer surface protein A (OspA) appears to protect mice against infection by the agent of Lyme disease, all reported experiments have involved formulations that would not be suitable for use in humans or have not used realistic challenges. This study was designed to determine whether vaccines prepared and used in a phase I human trial, including one currently being used for a phase II trial in sites with endemic Borrelia burgdorferi, conferred protection in the C3H/HeJ mouse model. The challenge was ticks collected from a major site of the trial. None of the vaccinated mice became infected or developed disease, whereas 60% of unvaccinated mice became infected. Spirochetes were destroyed within the guts of virtually all recovered challenge ticks. These preparations of recombinant OspA effectively induced immunity to protect mice from Lyme disease when bitten by ticks collected from a field trial site.

The Lyme disease vaccine candidate outer surface protein A (OspA) in a formulation compatible with human use protects mice against natural tick transmission of B. burgdorferi

Development of a vaccine for the Lyme disease spirochete, Borrelia burgdorferi, has focused on the bacterial lipoprotein, major outer surface protein A (OspA). With few exceptions, testing of OspA vaccines in animal models has involved challenge with needle inoculation of cultured spirochetes. Recombinant OspA proteins from two OspA divergent strains of B. burgdorferi were tested for their vaccine potential in three different strains of mice challenged with laboratory reared ticks with a high rate of B. burgdorferi infection. All formulations of the B. burgdorferi sensu stricto derived OspA vaccine protected all strains of mice when challenged by ticks infected with an OspA homologous strain of the spirochete, whereas heterologous OspA from B. afzelii did not protect. Furthermore, ticks feeding on protected mice had reduced OspA levels compared to unvaccinated controls.

Simultaneous presence of different Borrelia burgdorferi genospecies in biological fluids of Lyme disease patients

Oligonucleotide primers based on Borrelia burgdorferi sensu lato ospA gene sequences have been designed for use in the PCR to type all (SL primers) or each (GI to GIII primers) of the B. burgdorferi sensu lato genospecies involved in Lyme disease. These genospecies-specific primers were then used in the PCR on 24 biological fluids collected from 18 neuroborreliosis patients. Among the samples tested, 20 contained DNA from Borrelia garinii, 11 contained DNA from B. burgdorferi sensu stricto, and 10 contained DNA from Borrelia afzelii. In toto, 10 patients appeared to have been infected by a single genospecies and 8 were infected by more than one Lyme disease-associated genospecies. Serum specimens from six patients were absorbed with heterologous antigens and tested by Western blotting (immunoblotting). In four cases, residual immunodetection revealed specific epitopes of genospecies also detected by PCR; in two of them, the concordant results indicated pluri-infection of the patients. In the other two cases, Western blotting showed specific antibodies for two genospecies of Borrelia, while PCR detected DNA from only one. In summary, the data underscored the relatively high prevalence of pluri-infections in Lyme disease and confirmed the association of B. garinii with neuroborreliosis.

Vaccination against Lyme disease caused by diverse Borrelia burgdorferi

Diversity and mutations in the genes for outer surface proteins (Osps) A and B of Borrelia burgdorferi sensu lato (B. burgdorferi), the spirochetal agent of Lyme disease, suggests that a monovalent OspA or OspB vaccine may not provide protection against antigenically variable naturally occurring B. burgdorferi. We now show that OspA or OspB immunizations protect mice from tick-borne infection with heterogeneous B. burgdorferi from different geographic regions. This result is in distinct contrast to in vitro killing analyses and in vivo protection studies using syringe injections of B. burgdorferi as the challenge inoculum. Evaluations of vaccine efficacy against Lyme disease and other vector-borne infections should use the natural mode of transmission and not be predicated on classification systems or assays that do not rely upon the vector to transmit infection.

Assignment of Borrelia burgdorferi strains G25 and VS461 to the Borrelia garinii and Borrelia afzelii genospecies, respectively: a comparison of OspA protein sequences

The nucleotide sequence encoding the Outer Surface Protein A (OspA) from two Borrelia burgdorferi sensu lato isolates, G25 and VS461, has been determined. On the basis of a phylogenetic analysis, strains G25 and VS461 were respectively assigned to the B. garinii and B. afzelii genospecies. Comparative analysis of OspA proteins from 26 different B. burgdorferi sensu lato strains involved in Lyme disease indicated a higher heterogeneity in the B. garinii genospecies than in the two other genospecies, B. burgdorferi sensu stricto and B. afzelii.

Tick transmission of Borrelia burgdorferi to inbred strains of mice induces an antibody response to P39 but not to outer surface protein A

Natural tick transmission of infection by Borrelia burgdorferi induces a very different serum antibody response than needle inoculation of spirochetes. We present data, obtained by using the mouse model, that show that the OspA response was barely detectable, whereas all animals developed significant anti-P39 titers after exposure to B. burgdorferi-infected ticks.

Immunization of mice by recombinant OspA preparations and protection against Borrelia burgdorferi infection induced by Ixodes ricinus tick bites

The wide distribution of Borrelia burgdorferi, the spirochete causing Lyme borreliosis, represents a human health hazard in many areas of the world. Vaccination has been proposed as an effective prevention strategy. Vaccination experiments were conducted with preparations of recombinant outer surface protein A (OspA) derived from Borrelia burgdorferi strain ZS7. Mice received three doses (1 microgram each) of the antigens adsorbed to aluminum hydroxide. A strong immune response to the vaccine antigen was observed. Mice were challenged after immunization, using Ixodes ricinus nymphal ticks infected with Borrelia burgdorferi strain ZS7. Infection was investigated by ear biopsy culture, xenodiagnosis with uninfected larvae and serological response to Borrelia burgdorferi antigens. All unimmunized control animals were found to be infected, while all immunized animals were found to be protected against infection by Borrelia burgdorferi. In addition, most adult ticks derived from nymphs that fed on immunized mice were found to be free of spirochetes.

Site-specific alterations in the B oligomer that affect receptor-binding activities and mitogenicity of pertussis toxin

Pertussis toxin plays a major role in the pathogenesis of whooping cough and is considered an important constituent of vaccines against this disease. It is composed of five different subunits associated in a molar ratio 1S1:1S2:1S3:2S4:1S5. The S1 subunit is responsible for the ADP-ribosyltransferase activity of the toxin. The B moiety, composed of S2 through S5, recognizes and binds to the target cell receptors and has some ADP-ribosyltransferase-independent activities such as mitogenicity. Site-directed mutagenesis of subunits S2 and S3 allowed us to identify amino acid residues involved in receptor binding. Of all the modifications generated, the deletion of Asn 105 in S2 and of Lys 105 in S3 resulted in the more drastic reduction of binding to haptoglobin and CHO cells, respectively. A holotoxin carrying both deletions presented a mitogenicity reduced to an undetectable level. The combination of these B oligomer mutations with two substitutions in the S1 subunit led to the production of a toxin analog with reduced ADP-ribosyltransferase-dependent and -independent activities including mitogenicity. As shown by immunoprecipitation with various monoclonal antibodies, the mutant holotoxin was correctly assembled and antigenically similar to the native toxin. This toxin analog induced toxin-neutralizing antibodies at the same level as the holotoxin carrying only mutations in the S1 subunit, and may therefore be considered a useful candidate for the development of a new generation vaccine against whooping cough.

Evaluation of genetic divergence among Borrelia burgdorferi isolates by use of OspA, fla, HSP60, and HSP70 gene probes

In order to assess the genetic variation of immunologically relevant structures among isolates of the Lyme disease spirochete, Borrelia burgdorferi, three chromosomal genes encoding flagellin (fla) and the heat shock proteins HSP60 and HSP70, as well as the plasmid gene encoding outer surface protein A (OspA), from 55 different European and North American strains obtained from ticks and mammal hosts have been investigated by restriction fragment length polymorphisms (RFLPs). RFLPs of fla and the HSP60 and HSP70 genes revealed two distinct banding patterns (A and B) for each of the three genes and allowed the definition of four genomic groups [AAA, BBB, BBA, and B(A/B)A] for the three chromosomal genes. On the other hand, RFLPs of the OspA gene revealed six distinct banding patterns (types I to VI) making up six independent genomic groups for the plasmid-encoded gene. Furthermore, we have sequenced the chromosomal HSP60 gene from B. burgdorferi ZS7 and the plasmid-encoded OspA gene from two strains, ZQ1 and 19857. Alignment of the deduced HSP60 amino acid sequence from B. burgdorferi ZS7 (genomic group AAA) to a previously published HSP60 sequence derived from strain ACA-1, which according to the proposed classification is in a different genomic group (BBA), revealed a sequence identity of > 99%. Similar alignments of the OspA sequence of strain ZQ1 to those of other isolates that were published previously revealed sequence identities of between 70 and 94% among strains of distinct OspA genomic groups. These data indicate the existence of a restricted number of species-specific subgroups and clearly show that genotypic variation is much more pronounced for the OspA gene than for fla and the HSP60 and HSP70 genes. A phylogenetic tree constructed on the basis of distance matrix analyses of 12 OspA sequences supports the proposed classification of genomic groups of B. burgdorferi.

Effect of site-directed mutagenic alterations on ADP-ribosyltransferase activity of the A subunit of Escherichia coli heat-labile enterotoxin

Previous studies of the S1 subunit of pertussis toxin, an NAD(+)-dependent ADP-ribosyltransferase, suggested that a small amino-terminal region of amino acid sequence similarity to the active fragments of both cholera toxin and Escherichia coli heat-labile enterotoxin represents a region containing critical active-site residues that might be involved in the binding of the substrate NAD+. Other studies of two other bacterial toxins possessing ADP-ribosyltransferase activity, diphtheria toxin and Pseudomonas exotoxin A, have revealed the presence of essential glutamic acid residues vicinal to the active site. To help determine the relevance of these observations to activities of the enterotoxins, the A-subunit gene of the E. coli heat-labile enterotoxin was subjected to site-specific mutagenesis in the region encoding the amino-terminal region of similarity to the S1 subunit of pertussis toxin delineated by residues 6 through 17 and at two glutamic acid residues, 110 and 112, that are conserved in the active domains of all of the heat-labile enterotoxin variants and in cholera toxin. Mutant proteins in which arginine 7 was either deleted or replaced with lysine exhibited undetectable levels of ADP-ribosyltransferase activity. However, limited trypsinolysis of the arginine 7 mutants yielded fragmentation kinetics that were different from that yielded by the wild-type recombinant subunit or the authentic A subunit. In contrast, mutant proteins in which glutamic acid residues at either position 110 or 112 were replaced with aspartic acid responded like the wild-type subunit upon limited trypsinolysis, while exhibiting severely depressed, but detectable, ADP-ribosyltransferase activity. The latter results may indicate that either glutamic acid 110 or glutamic acid 112 of the A subunit of heat-labile enterotoxin is analogous to those active-site glutamic acids identified in several other ADP-ribosylating toxins.

The role of cysteine 41 in the enzymatic activities of the pertussis toxin S1 subunit as investigated by site-directed mutagenesis

The S1 subunit (Mr 28,000) of pertussis toxin expresses thiol-dependent enzymatic ADP-ribosyltransferase and NAD-glycohydrolase activities. Site-directed mutagenesis experiments were performed on the codon for Cys-41 of this subunit to investigate the role of this residue in both enzymatic activities. Deletion of Cys-41 caused a decrease in both activities below detectable levels, whereas replacement of this residue by serine, glycine, proline, or asparagine only slightly reduced the activities. The enzymatic activities of these mutants were thiol-independent. The deletion of Ser-40, adjacent to Cys-41, again caused reduction of the enzymatic activities to undetectable levels. Steady-state kinetic experiments showed that the kcat of the mutant protein in which Cys-41 was replaced by glycine was nearly identical to the kcat of the parent version. However, the Km for NAD of the mutant was significantly higher relative to that of the wild type version. These results indicate that the side-chain of Cys-41 is not essential for enzymatic activities and that Cys-41 is not involved in the rate of catalysis but is probably located at or close to the NAD-binding site. The introduction of a negative charge at position 41 through the replacement of Cys-41 by either aspartate or glutamate reduced the enzymatic activities to very low but measurable levels, suggesting a charge-charge repulsive interaction between these residues and possibly one or both of the phosphates of NAD. Cys-41 may therefore be located close to the phosphate subsite of the NAD-binding site.

Effects of mutations on enzyme activity and immunoreactivity of the S1 subunit of pertussis toxin

By introducing a series of six different substitutions at and around position 9, we investigated the structural requirements of the amino-terminal region of the S1 subunit of pertussis toxin for both enzyme activity and immunoreactivity. All mutant S1 analogs with a substitution at this location exhibited severely decreased ADP-ribosyltransferase activity (range, 400- to 2,500-fold). In contrast, alteration of arginine 58 had considerably less effect. The reactivity of the mutant molecules with monoclonal antibody 1B7 varied with the nature of the substitution. These findings indicate an absolute requirement for the presence of an arginine residue at position 9 for the maintenance of efficient ADP-ribosyltransferase activity and illustrate the specific participation of vicinal residues in the formation of the protective epitope.

Partial purification and characterization of the specific protein-lysine N-methyltransferase of YL32, a yeast ribosomal protein

YL23 and YL32 are two of the three most heavily methylated ribosomal proteins of Saccharomyces cerevisiae. Using an in vitro assay, it was determined that they are methylated by two distinct enzymes. The protein-lysine N-methyltransferase that methylates YL32 was partially purified by affinity and ion-exchange chromatography. Its molecular mass was estimated to be 82 kDa, and its isoelectric point to be 4.45. Optimum activity was expressed at pH 7.5, and the enzyme was irreversibly inactivated at pH lower than 5.0. The Km of the enzyme for AdoMet is 1.7 +/- 0.4 microM, and the Ki toward AdoHcy was 0.71 microM. Formation of epsilon-N-dimethyllysine was observed to occur in two steps via epsilon-N-monomethyllysine. Like other protein-lysine N-methyltransferases, the methylase of YL32 exhibits a high substrate specificity.

Frame-shift mutation in the lacZ gene of certain commercially available pUC18 plasmids

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Methylated proteins and amino acids in the ribosomes of Saccharomyces cerevisiae

The occurrence of methylated proteins in the ribosomes of Saccharomyces cerevisiae was investigated by tracing the transfer of radioactive methyl groups from S-adenosyl methionine, taken up by growing cells, into the protein moiety of ribosomes. It was estimated that the large subunit contained about 10 protein-bound methyl groups distributed mainly among proteins YL23, YL32 and YL1. The small subunit contained at most 2-4 methyl groups in proteins. Methyl groups could be transferred in vitro to proteins YL23 and YL32 in extracts from cultures of an S-adenosyl methionine auxotroph deprived of the methyl-group donor. In the most heavily methylated proteins the methylated amino acids formed in vitro were the same as those found in vivo (monomethyllysine and dimethyllysine in YL32; dimethyl and trimethyllsine in YL23). It is concluded that the enzymatic reaction in vitro faithfully saturates with methyl groups the target amino acids which are normally fully methylated in vivo.