Apple domain (IPR000177)

Short name: Apple

Overlapping homologous superfamilies


Domain relationships


Plasma kallikrein (EC: and coagulation factor XI (EC: 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 [PMID: 1998666] that three disulphide 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
                     .....x     x.....
Apart from the cysteines, there are a number of other conserved positions in the apple domain. The apple domains of plasma prekallikrein are known to mediate its binding to high molecular weight kininogen [PMID: 8662705], the apple domains of factor XI bind to factor XIIa, platelets, kininogen, factor IX and heparin [PMID: 9632702].

GO terms

Biological Process

GO:0006508 proteolysis

Molecular Function

GO:0005515 protein binding

Cellular Component

GO:0005576 extracellular region

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE patterns