ANTIBODIES BINDING ANTIGENS - Analytical Molecular Biology - page 4

Each sequence consists of approximately 214 amino acid residues as listed
from the N-terminal to the C-terminal. The sequences of the first 107 amino
acid residues of the three proteins were different, and Hilschmann and Craig
designed that portion of these proteins as the variable region. On the other
hand, the remaining 107 amino acid residues, i.e. from position 108 to 214,
had the same sequence except possibly two or three positions. Thus, that
portion was known as the constant region. They made a crucial prediction,
i.e. the variable and constant regions of the same protein were coded by two
different genes.
To sequence the heavy chains of immunoglobulins or antibodies, they have
to be isolated from serum myeloma proteins of patients suffering from
multiple myeloma. That was achieved about five years later. They are in
general about twice as long as the light chains. For example, one of the first
completely sequenced heavy chains, EU (Edelman et al ., 1969), has 446
amino acid residues. Another, OU (Putman et al ., 1973), has 576 residues.
The N-terminal quarter of these sequences are highly varied as the N-
terminal half of the light chains. The remaining three-quarter of the heavy
chain can roughly be divided into three similar regions. Between the first
and second regions, there is usually a short segment rich in Cys residues
known as the hinge region.
A schematic representation of an antibody molecule is shown in Fig. 1-2
(see, for example, Kabat et al ., 1991). It consists of two heavy and two light
chains. As discussed before, the light chain can be divided into a variable,
V L , and a constant, C L , region, while the heavy chain into V H , C H 1, hinge,
C H 2 and C H 3 regions. In some cases, the hinge region is absent, and there is
an additional C H 4 region. Amino acid residues are numbered from the N-
terminal ends. Nearly every researcher has a different numbering system.
However, alignment will be very important to further analyze these
sequences. We are thus going to use the Kabat numbering system (Kabat et
al ., 1991) which has been generally adopted by many investigators in this
field.
Each of us can produce two different types of light chain constant regions,
known as kappa or and lambda or Their genes are located on two
different chromosomes, 2p11 (Malcolm et al ., 1982) and 22q11 (Erikson et
al ., 1981; Emanuel et al ., 1985) respectively. We can also produce several
different heavy chain constant regions, known as etc. and some
minor variations of these. Their genes are all located consecutively on the
same chromosome, 14q32 (Croce et al ., 1979; McBride et al ., 1982).