488
Autoimmunity in Scleroderma
to anaphase. Rattner et al. reported that
autoantibodies to CENP-F were found
mainly in patients who suffered from
malignant tumors but not systemic au-
toimmune disease and rarely found them
in ‘‘classical’’ ACA-positive sera, which de-
tect CENP-A, B, and C. Its cDNA was also
isolated by immunoscreening with human
autoantibodies, while a cDNA that encoded
human CENP-E was isolated using exper-
imentally induced monoclonal antibodies
by immunization of fractionated chromo-
somal proteins. CENP-H cDNA was inci-
dentally obtained by differential display.
cDNA clones of CENP-D and -G, which
were also shown to be recognized by ACA,
have not been obtained. Although sev-
eral proteins that are not named ‘‘CENP’’
are known to exist in the centromere
region – centromere-chromatin
proteins
and centromere-associated proteins – they
are rarely targeted by ‘‘classical’’ ACA.
2.2
CENP-B and B-cell Epitopes
We start with CENP-B epitopes since its
gene was cloned at ±rst and has been
most extensively studied. CENP-B has
599 amino acid residues and an appar-
ent molecular mass of 80 kDa, larger than
the predicted molecular weight of 65 kDa.
This antigen was used for the demon-
stration of the direct interaction between
the constitutive centromeric protein and
centromeric satellite DNA (alphoid DNA).
Alphoid DNA is a long, tandemly re-
peated DNA family based on a 171 bp
fundamental monomer repeat unit. The
alphoid DNA family in humans is com-
posed of many subclasses, which share
varying degrees of sequence homology
(60–90%) and have been localized to the
primary constriction (centromere) of spe-
ci±c chromosomes. Masumoto et al. found
that the CENP-B antigen directly interacts
with an alphoid DNA and they named
the 17 bp motif required for the speci±c
binding ‘‘CENP-B box.’’ The DNA bind-
ing domain of CENP-B is located within
the N-terminal 125–amino acid region
containing 4 potential
α
-helices. On the
contrary, the C-terminus of the protein
from 541 to 599 amino acids forms a ho-
modimer by itself (Fig. 3). Thus, CENP-B
was presumed to contribute to the forma-
tion of the heterochromatin structure in
the centromere region, binding to alphoid
1
125
541
DNA
binding domain
Dimerization
domain
403
507
599
466
539
535
599
438
492
17
3
Epitope III
+
IV
Epitope II
Epitope I
Fig. 3
Functional domains and autoepitopes of CENP-B. The top rectangle represents the
full-length human CENP-B antigen. Two horizontal lined boxes show highly acidic regions.
Major autoepitopes, which are recognized by more than 50% of ACA, are shown as black
bars. Minor epitope, which is recognized by less than 50% of ACA, is shown as a white bar.
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