{PDOC00262}
{PS00290; IG_MHC}
{BEGIN}
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* Immunoglobulins and major histocompatibility complex proteins signature *
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The basic structure  of immunoglobulin (Ig) [1] molecules is a tetramer of two
light chains  and two heavy chains linked  by disulfide  bonds.  There are two
types of  light chains:  kappa and lambda,  each composed of a constant domain
(CL) and a variable domain (VL).  There are five types of heavy chains: alpha,
delta, epsilon,  gamma  and  mu,  all consisting of a variable domain (VH) and
three (in alpha,  delta  and  gamma)  or  four (in  epsilon and  mu)  constant
domains (CH1 to CH4).

The major histocompatibility complex  (MHC) molecules  are made of two chains.
In class I [2] the alpha  chain is composed of three  extracellular domains, a
transmembrane   region   and a   cytoplasmic tail.   The  beta  chain (beta-2-
microglobulin) is  composed of a single extracellular domain. In class II [3],
both the  alpha and the beta chains are composed of two extracellular domains,
a transmembrane region and a cytoplasmic tail.

It is  known  [4,5]    that  the  Ig  constant  chain  domains  and   a single
extracellular   domain   in each  type  of  MHC   chains are related.    These
homologous domains  are  approximately    one    hundred amino  acids long and
include a conserved intradomain disulfide bond.  We developed  a small pattern
around the C-terminal cysteine involved  in  this  disulfide bond which can be
used to detect these category of Ig related proteins.

-Consensus pattern: [FY]-{L}-C-{PGAD}-[VA]-{LC}-H
                    [The C is involved in a disulfide bond]
-Sequences known to belong to this class detected by the pattern:
 Ig heavy chains type Alpha C region  : All, in CH2 and CH3.
 Ig heavy chains type Delta C region  : All, in CH3.
 Ig heavy chains type Epsilon C region: All, in CH1, CH3 and CH4.
 Ig heavy chains type Gamma C region  : All, in CH3 and also CH1 in some cases
 Ig heavy chains type Mu C region     : All, in CH2, CH3 and CH4.
 Ig light chains type Kappa C region  : In all CL except rabbit and Xenopus.
 Ig light chains type Lambda C region : In all CL except rabbit.
 MHC class I alpha chains : All,  in   alpha-3  domains,   including   in  the
 cytomegalovirus MHC-1 homologous protein [6].
 Beta-2-microglobulin     : All.
 MHC class II alpha chains: All, in alpha-2 domains.
 MHC class II beta  chains: All, in beta-2 domains.
-Other sequence(s) detected in Swiss-Prot: 89.
-Last update: April 2006 / Pattern revised.

[ 1] Gough N.
     Trends Biochem. Sci. 6:203-205(1981).
[ 2] Klein J., Figueroa F.
     Immunol. Today 7:41-44(1986).
[ 3] Figueroa F., Klein J.
     Immunol. Today 7:78-81(1986).
[ 4] Orr H.T., Lancet D., Robb R.J., Lopez de Castro J.A., Strominger J.L.
     "The heavy chain of human histocompatibility antigen HLA-B7 contains
     an immunoglobulin-like region."
     Nature 282:266-270(1979).
     PubMed=388231
[ 5] Cushley W., Owen M.J.
     Immunol. Today 4:88-92(1983).
[ 6] Beck S., Barrell B.G.
     "Human cytomegalovirus encodes a glycoprotein homologous to MHC
     class-I antigens."
     Nature 331:269-272(1988).
     PubMed=2827039; DOI=10.1038/331269a0;

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