Found in tandem repeats of about 90 amino acids, the apple domain has six conserved cysteines arranged in three disulfide bonds: first to sixth, second to fifth, and third to fourth cysteines. The domain is aptly named for the two-dimensional representation generated when the disulfides are linked. In addition to the cysteines, there are a number of other conserved positions in the apple domain.

Schematic diagram of the apple domain.

Note that the disulfides are numbered according to their appearance in the sequence

The first apple domain from human factor XI