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gene to sequence an anti-idiotypic abzyme with ß-lactamase-like activity that could have a linkage with autoimmune diseases
UPRES A 6022 Génie enzymatique et cellulaire, Université de Technologie de Compiègne, BP 20529, 60205 Compiegne Cedex, France
1Correspondence: UPRES A 6022 Génie enzymatique et cellulaire, Université de Technologie de Compiègne, BP 20529, 60205 Compiegne Cedex, France. E-mail: lndebat{at}belgacom.net
| ABSTRACT |
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gene to bypass aberrant V
(abV
) produced by
MOPC-21-derived hybridomas. Sequences obtained are compared in the
GenBank database. The VH and V
genes present some important sequence
homology with autoantibodies suggesting a direct relationship between
catalytic anti-idiotypic antibody and autoimmunity.Débat, H.,
Avalle, B, Chose, O., Sarde, C.-O., Friboulet, A., Thomas, D.
Overpassing an aberrant V
gene to sequence an anti-idiotypic abzyme
with ß-lactamase-like activity that could have a linkage with
autoimmune diseases.
Key Words: catalytic antibody autoantibody aberrant kappa chain
| INTRODUCTION |
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We have developed a strategy aiming at eliciting antibodies that mimic
the active sites of enzymes. As proposed by Jerne (11)
,
anti-idiotypic antibodies can recognize some determinants of the
combining site of an antibody (Ab1) contacting the original antigen.
This concept was successfully applied from enzymatic active sites in
order to obtain anti-idiotypic antibodies mimicking the enzymatic
function of acetylcholinesterase (12
, 13)
and
beta-lactamase (14)
.
We report the universal cloning of antibody 9G4H9 displaying a
beta-lactamase-like activity, bypassing an aberrant
transcript
(abV
) first described by Carroll et al.
(15)
. The cloning presented some difficulties inherent in
the procedure used to obtain monoclonal antibodies (mAb). Indeed,
almost all mAb are isolated from hybridomas (16)
. This
method for producing antibodies has many advantages, especially the
ability to produce large amounts of pure antibody from ascitic fluids.
However, the hybridoma technology cannot be used directly to prepare
mutants in experiments designed to improve the catalytic activity of
the abzyme or to probe its mechanism (17)
. The presence of
aberrant transcript mRNA is also a major problem. In this report, we
present a strategy to bypass the abV
gene by taking
advantage of specific immunoglobulin leader sequence and framework 1
region information. These sequences are sufficiently variable and
homogeneous to take some primer sets to amplify the immunoglobulin
light chain of interest secreted by the hybridoma cells.
The nucleotide sequence of the variable domain of the heavy and the light chain gene of the 9G4H9 mAb was obtained and compared to database sequence. A tight homology with autoantibodies involved in autoimmune disease was observed. The possible link between autoimmunity and the appearance of catalytic anti-idiotypic antibodies are discussed.
| MATERIALS AND METHODS |
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DNA manipulations
Restriction enzymes (2 U/reaction) and ligation enzyme (5
U/reaction) were purchased from Eurogentec (Brussels, Belgium). Plasmid
DNA isolation was performed from overnight cultures with a QIAprep Spin
Plasmid Kit (Qiagen S.A., Courtaboeuf Cedex, France). DNA fragments
were purified by using the Geneclean III kit (BIO 101, Ozyme, Paris,
France) according to the manufacturers instructions.
First-strand cDNA synthesis of variable heavy (VH) and light
(V
) chain genes
In preparing polymerase chain reaction (PCR) amplification, the
cDNA synthesis reaction was performed with the SuperScriptTMII
RNAseH- Reverse Transcriptase (Gibco BRL, Grand
Island, N.Y.) using a specific primer for the heavy chain of
immunoglobulin G2b or kappa light chain. In a typical 20 µl
transcription reaction mixture, 1 µg of mRNA in water was first
annealed with 2 pmol of the 3'VH primer (primer 15, Table 1
) or the 3' V
primer (primer 1, Table 1
) at 70°C for 5 min in two
different tubes. The mixture was adjusted at room temperature with 50
mM Tris-HCl pH 8.3 containing 75 mM KCl, 3 mM
MgCl2, 1 mM DTT, and 500 µM each
deoxyribonucleoside triphosphate (dNTP) at neutral pH. The mixture is
incubated at 42°C for 2 min and 200 U of SuperScriptTMII was added.
The reaction was incubated 50 min at 42°C and inactivated by heating
at 70°C for 15 min. cDNA was purified to be used as a template to the
5' RACE procedure or PCR amplification.
|
Amplification of the VH and light chain (V
) genes using the 5'
RACE-PCR method
The method used was first described by Frohman et al.
(22)
. Terminal deoxynucleotidyl transferase (TdT;
Amersham, Little Chalfont, U.K.) was first used to add a poly(dG) tail
to the 3' end to the first-strand cDNA. To a microcentrifuge tube on
ice, 20 µl of cDNA template was added to 10 µl of 5x TdT reaction
buffer (5 mM 2-mercaptoethanol, 500 mM of sodium cacodylate pH 7.2, 40
mM MgCl2, 0.125% BSA, and 850 µg/ml activated
calf thymus DNA), 5 µl of a 10x MnCl2 buffer
(1 M sodium cacodylate, pH 7.2, 20 mM MnCl2, and
1 mM DTT), 0.8 µl of a solution of dGTP 25 mM, 14.2 µl of water and
20 U of TdT. The tube was incubated for 10 min at 37°C and the
reaction was terminated by adding 10 µl of 0.2 M EDTA.
The homopolymeric tailing cDNA (5 µl) was purified and amplified
using one primer specific for framework 4 domain of the heavy IgG2b
gene studied (primer 17, Table 1
) or for framework 4 domain of the
light chain gene (primer 3, Table 1
) and one specific to the
homopolymeric tail (primer 2, Table 1
). Amplification was carried out
in 10 mM Tris-HCl buffer pH 8.3 containing 50 mM KCl; 2 mM
MgCl2, 200 µM each dNTP, 100 pmol of primer
(primer 2, Table 1
) that anneals to the poly(dG) tail, 100 pmol of
primer 3 (Table 1)
specific to the
light chain, or primer 17 (Table 1)
specific to the IgG2b heavy chain genes, and the cDNA template in a
total volume of 100 µl. Reaction mixture were overlaid with mineral
oil (Sigma Chemical, St. Louis, Mo.) and heated at 94°C for 6 min
before addition of 2.5 units of the AmpliTaq Gold DNA polymerase
(Perkin Elmer, Norwalk, Conn.). The PCR products were then cycled 30
times as follows: denatured for 1 min at 94°C, annealed for 1 min at
58°C, and extended for 1 min at 72°C in a Thermocycler (Perkin
Elmer). An additional 6 min extension at 72°C was performed and then
reactions were held at 4°C. Reaction products were electrophoresed
through 1% agarose gels (Eurogentec) and visualized with ethidium
bromide (Sigma Chemical). The DNA band of interest was excised and
purified.
Cloning and sequencing of the VH and V
genes
PCR products were digested with the corresponding restriction
enzyme, purified, cloned into pBluescript II KS (+) (Stratagene, San
Diego, Calif.; Ozyme), and transformed into competents
Escherichia coli JM109 cells according to the method
described by Sambrook et al. (19)
. Transformants were
selected on solid Luria-Bertani medium containing 50 µg
ml-1 ampicillin. Sequencing of the cDNA was
performed by GenomeExpress (CEA Grenoble, France). The numbering of
residues and determination of the complementary defining region (CDR)
position was according to Kabat et al. (23)
.
Sequence alignments
Sequence alignment analysis was carried out using the French
Server BISANCE. The homologies between our sequences and the database
sequences in EMBL/GenBank/DDBJ were determined by CLUSTAL W program
(24)
.
Nucleotide sequence accession numbers
The nucleotide sequences of the variable regions V
and VH of
the 9G4H9 catalytic antibody presented in this study have been assigned
accession numbers aj277812 and aj277813,
respectively, by EMBL.
| RESULTS |
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chain gene of 9G4H9
light chain, we first used the
5'RACE-PCR strategy to clone the gene. Among the 27 clones sequenced,
we obtained only the aberrant
light chain (abV
). This
abV
was previously described by Carroll et al.
(15)
was derived from the fusion partner SP2/0 used
to make hybridoma with splenocytes from mice immunized. Indeed, SP2/0
was used in the case of the generation of Ab2, the 9G4H9 catalytic
antibody with a beta-lactamase activity (14)
transcript is variable and
may exceed levels of the productive light chain mRNA.
This problem was solved by using the same 3' end toward primer of the
antibody V
domain (primer 3, Table 1
) and the collection of 5' end
toward primers that hybridize to the leader sequences of mouse
light chains (primers 10 to 14, Table 1
) (25)
. Results
obtained were approved using a unique set of VL gene family-specific
primers described by Nicholls et al. (26)
(primer 4 to 9,
Table 1
) that hybridize to the framework 1. These primers were chosen
because they were different enough from the 5' end of the
abV
to obtain 9G4H9 cDNA light chain. Results of PCR
amplification are shown in Fig. 1
. Figure 1A
shows amplification with the primers that
hybridize to the leader sequences of mouse
chain (25)
.
Five primers were tested: MKVP2, the control that hybridizes with the
leader sequence of the aberrant
light chain, and four primers
(MKVP1, 6, 8, 11) different enough from the MKVP2 leader sequence. The
results show a sharp DNA band at the predicted size of 400 ± 20
pb with MKVP2 and a good amplification with MKVP6. No amplification
with the others primers (MKVP1, 8, 11) was obtained. MKVP6 was largely
different from MKVP2 and thus might have amplified the 9G4H9 mRNA. This
result demonstrates that the level of abV
mRNA is clearly
higher than 9G4H9 mRNA in the hybridoma cells as demonstrated by
Carroll et al. (15)
. MKVP6 amplified fragment was purified
and cloned in pBluescript II SK (+), sequenced, and analyzed. The
sequence is presented in Fig. 2
and corresponds to a functional
light chain. To confirm that this
sequence amplification is the only sequence expressed corresponding to
9G4H9 catalytic antibody, we consecutively tested 6 primers to the
framework 1 previously described by Nicholls et al. (26)
(primers 4 to 9, Table 1
) paired with the same primer to the toward 3'
end (primer 3, Table 1
). The results in Fig. 1B
show
different levels of amplification according to the primer used. The
primers in lane 1, 3, 4, and 5 (VL-I/III, VL-IIb, VL-Va, and VL-5b),
which hybridize with abV
sequence, show a high level of
amplification with a DNA band at the predicted size of 350 ± 20
pb. The amplification level in lane 2 and 6 is low. These amplification
fragments were purified, restricted, and cloned into pBluescript II SK
(+) and the sequences were analyzed. Of all the sequences analyzed,
only the sequence obtained by amplification with the primer
VL-IIb was different from abV
. This sequence
corresponds to the same sequence previously obtained with primer MKVP6
and is shown in Fig. 2
(accession number aj277812 in
EMBL/GeneBank/DDJB databases).
|
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Cloning and sequencing of the VH gene of 9G4H9
The variable domain of the heavy chain VH was cloned after
first-strand cDNA synthesis (primer 15, Table 1
) and 5'RACE-PCR
amplification from a total mRNA preparation of hybridoma cells. PCR was
performed with a 5' end toward primer (primer 16, Table 1
) and a 3' end
toward primer (primer 17, Table 1
). Unique amplification products were
obtained (Fig. 3
) at the predicted size of 400 ± 40 pb modulated by the size of the
homopolymeric tail and the hybridization site of the corresponding
primer (primer 16, Table 1
) used to perform the PCR amplification. Each
PCR product was inserted into the pBluescript II SK (+) plasmid and DNA
sequencing was performed. The nucleotide sequence of the VH domain of
the 9G4H9 antibody was obtained, and the deduced amino acid sequence is
given in Fig. 4
. The corresponding accession number to EMBL/GenBank/DDBJ is
aj277813.
|
|
Sequence alignment of VH and V
gene of 9G4H9 to database
sequences
The VH and V
sequences were compared with other sequences
in the data bank. The best homology sequences are shown in Fig. 5
. All the mouse origin sequences present an important homology with our
heavy (at least 86%) or light (at least 92%) variable chains and are
involved in a catalytic or anti-idiotypic mechanism.
|
The VH sequences noted by the accession numbers musikcls,
mmu6946, and u00940 correspond to antibodies that
are involved in autoimmune diseases (27
28
29)
. The first VH
sequence was described in mice that spontaneously develop a systemic
lupus erythematous-like disease. The second sequence mmu6946
was previously described in spontaneous murine B cell tumors, and the
authors have demonstrated that the sequence is closely similar to
antibodies found in corresponding human diseases. The third homologous
sequence u00940 corresponds to a nucleic acid binding
antibody from autoimmune mice-derived, bacteriophage-displayed
libraries. Among the other sequences that present a high level of
similarity with the VH domain of 9G4H9 sequence
aj277813, the VH sequence musig4c11a corresponds
to a stimulatory anti-idiotypic antibody that induces different
anti-phosphorylcholine responses (30)
. The
musigaza sequence corresponds to the gamma chain mRNA
V region of a catalytic antibody with chorismate mutase activity
(31)
and the a27941 sequence corresponds to
humanized and chimeric monoclonal antibodies from a patent (no
reference).
When the V
domain of 9G4H9 is compared to the GenBank database
sequences, we also obtain an important homology with the V
gene
indirectly [(af087033 (32)
] or directly
involved in natural autoimmune processes
[af045515, no reference; mmu92070
(33)
; af045509, no reference;
musigkcsc (34)
; and af057543
(35)
].
| DISCUSSION |
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mRNA and cloning a functional antibody
light chain
chain cDNA sequences from hybridoma cells having
SP2/O as a parent cell. This cell line has been selected from MOPC-21
myeloma for its nonexpression of the normal
by different mutation
and rearrangement chains (37)
sequence of 9G4H9 catalytic
antibody, but only an aberrant transcript abV
that had an
aberrant VJ recombination site (15
chains and have a
wild-type leader signal sequence and FR-1. Many groups reported its
preferential amplification by RT-PCR when attempting to clone the light
chain of hybridomas derived from B cells fused to this fusion partner
(26
. They used a specific RNase H digestion of this V
pseudogene mRNA. The specific digestion was directed by an antisense
oligonucleotide (5' GTAAGCTCCCTAATGTGCTG 3'), which can only bind to
the abV
mRNA and not to the unknown sequence of the V
domain of the clone of interest. RNase H can then specifically digest
the abV
mRNA in the resulting double-stranded RNA-DNA
hybrid (45)
domain sequence, but 45% of homology between this antisense
oligonucleotide and the right V
sequence of kappa light V
of
9G4H9 was sufficient to destroy all mRNA (data not shown). The trouble
arises from the temperature of 42°C used for the specific digestion
by RNase H. This temperature is too low to permit a specific annealing.
Therefore, the successful and general application of PCR to the rapid
cloning of variable regions of rearranged immunoglobulin genes requires
a careful design of universal primers. This system functions by
taking advantage of the finding that mammalian light and heavy chains
of immunoglobulins contain conserved regions, adjacent to the
hypervariable CDR. Thus, appropriately designed oligonucleotide
degenerated primer sets allow these regions to be specifically
amplified by PCR (25
, 46
47
48)
. To develop a set of
compatible primers for mouse antibodies, several laboratories pooled
and aligned the murine antibody sequences collected in the Kabat
database (23)
. These primers can be based on either the
immunoglobulin leader region (amino acids -20 to -13) or the
framework region 1 (FR-1) (amino acids 17 or 8). Similar sequences
were grouped, and putative primer sequences were then compared to the
pooled sequences, and the best fit primer sequence was selected.
This process was repeated until all the sequences were evaluated. This
allowed optimization of the degenerate primers to cover 5' end
immunoglobulin DNA sequences as much as possible for PCR amplification.
In attempt to solve the problems outlined above, we have used a simple
PCR-based technique for cloning and sequencing the V
sequence of
9G4H9 catalytic antibody by using two steps of PCR amplification to
confirm the rightness of the sequence cloned. The first step uses a
degenerated oligonucleotide primers set described by Jones and Bendig
(25)
that hybridizes to the mouse immunoglobulin leader
sequences of
light chain (primers 10 to 14, Table 1
), paired with a
primer that hybridizes to the framework 4 to performed a PCR
amplification. The second step confirms the first results by using the
degenerated primers covering the framework 1 region.
Analysis of the V
and the VH genes of the catalytic antibody
9G4H9 displaying a beta-lactamase activity: a possible
relationship with autoimmune disease
Generation of antibodies that catalyze the opening of the
beta-lactam ring of antibiotics, naturally performed by microbial
beta-lactamases, appears to be an appropriate model to demonstrate the
relevance of the anti-idiotypic mimicry scheme. A monoclonal
anti-idiotypic antibody 9G4H9 (Ab2) was elicited by using a monoclonal
antibody 7AF9 (Ab1) specific for the beta-lactamase active site and its
catalytic activity was characterized (14)
. Analysis of the
primary sequence of the
light chain and the heavy chain fragments
did not show any significant homology with the primary structure of the
model enzyme. Thus, the anti-idiotypic abzyme active center probably
does not possess a direct imprint of its enzyme ancestor at the primary
structure level. The catalytic antibody active site seems to be a
3-dimensional copy of the beta-lactamase active site. As the catalytic
properties are different, we create in the antibody a replica of the
enzyme-active site with errors. The topological information is
conserved enough to induce Ab3 (14)
, which recognize
beta-lactamase, and to preserve the expression of catalytic residues in
a correct position and orientation necessary for functioning of the
hydrolytic machinery. As a first approach, identification of potential
residues involved in catalytic activities of 9G4H9 was performed, which
suggests that an acidic residue and a nucleophilic group are present in
9G4H9 (49)
. The molecular modeling of this 9G4H9 antibody
constructed with the Swiss-Pdb Viewer program using a homologous
antibody of known structure for the input coordinates confirms this
hypothesis (50)
. In this model, four residues in the
light chain were found correctly positioned to be involved in a
possible beta-lactam hydrolysis mechanism: Ser26, Ser28, Lys27 in
CDRL1, and Glu98 in CDRL3. This hypothesis was recently demonstrated by
Western blot and ELISA experiments, which indicate the
light chain
forms a covalent complex with the penicillin substrate
(51)
. Prior to the design and construction of the 9G4H9
scFv fragment, it was important to carefully analyze the amino acid
sequence of variable domains to determine the germline and compare
it with another antibody in the immunoglobulin database. The results
show a sequence homology with antibodies involved in catalytic process
and related in autoimmune disease. The germline of all the sequences is
the same: V
-II for light chain and VH-II for heavy chain.
Somatic mutations are observed in VH domain and V
domain by a
comparison with the germline. This indicates evidence for antigen
selectionclustering of replacement mutations in regions like that
observed in the literature (52
53
54)
. The germline
mutations observed in the 9G4H9 CDRL3 showing Ser96, Tyr55, and Glu98
seem to be crucial for inducing beta-lactamase affinity and activity.
These acidic and nucleophilic residues could have an important role in
catalytic activity. Several roles of hydrogen bonds are assigned to Tyr
residues in catalytic antibodies with esterase activity
(5)
. Three important roles in catalytic mechanisms are
described: stabilization of complex, orientation of two faces of ester
carbonyl, and interaction with water molecules, which gives rise to the
attacking hydroxide ion. In addition to the residues described in a
molecular model like Glu98 (50)
, Ser96 is very important
to the affinity of substrate and catalytic mechanism of opening of the
beta-lactam ring. The hypothesis that the
light chain is involved
in catalytic process agrees with some reports (55
56
57
58)
.
The light chain alone can also be involved in binding a substrate in
autoimmune disease (59
60
61
62)
. Mimicry of enzymatic sites by
anti-idiotypic antibodies resulting from immune regulation dysfunction
has been proposed several times to explain the appearance of abzymes in autoimmune disorders (63
64
65
66)
or discuss a
possible role in metabolism (67)
. Moreover, Tawfik et al.
(68)
and Takahashi et al. (69)
reported an
unexpectedly high occurrence of autoimmune mice to elicit catalytic
antibodies. In this report, we show a direct sequence homology
between a catalytic antibody and other autoantibodies. Thus, our
results present evidence for a correlation between the catalytic
anti-idiotypic antibodies created in laboratory made by mimic
concept and natural autoantibodies.
| ACKNOWLEDGMENTS |
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Received for publication June 23, 2000. Accepted for publication August 18, 2000.
| REFERENCES |
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