****************
* Apple domain *
****************

Plasma kallikrein (EC 3.4.21.34) and  coagulation factor XI (EC 3.4.21.27) are
two related plasma serine proteases activated  by  factor XIIA and which share
the same  domain  topology:  an  N-terminal  region  that contains four tandem
repeats of about 90 amino acids and a C-terminal catalytic domain.

The 90 amino-acid repeated domain contains 6 conserved cysteines.  It has been
shown [1,2] that three  disulfide bonds  link the first and sixth,  second and
fifth, and third and fourth cysteines. The domain can be drawn in the shape of
an apple (see below) and has been accordingly called the 'apple domain'.

                      x x x     x x x
                    x      C---C      x
                   x      x     x      x
                  x       Cx x  x       x
                  x       |  x  x       x       Schematic representation of an
                  x       Cx x  x       x       apple domain.
                   x      x     x      x
                    x     x     x     x
                     x     x x x     x
                      x             x
                        x x     x x
                           C---C
                     .....x     x.....

Apart from the  cysteines,  there are a number of other conserved positions in
the apple domain. We have developed a pattern, that spans the complete domain,
and which includes these conserved positions.

-Consensus pattern: C-x(3)-[LIVMFY]-x(5)-[LIVMFY]-x(3)-[DENQ]-[LIVMFY]-x(10)-
                    C-x(3)-C-T-x(4)-C-x-[LIVMFY]-F-x-[FY]-x(13,14)-C-x-
                    [LIVMFY]-[RK]-x-[ST]-x(14,15)-S-G-x-[ST]-[LIVMFY]-x(2)-C
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: NONE.
-Last update: June 1992 / Pattern and text revised.

[ 1] McMullen B.A., Fujikawa K., Davie E.W.
     Biochemistry 30:2050-2056(1991).
[ 2] McMullen B.A., Fujikawa K., Davie E.W.
     Biochemistry 30:2056-2060(1991).