The BRCA2 helical domain adopts a helical structure, consisting of a four-helix cluster core (alpha 1, alpha 8, alpha 9, alpha 10) and two successive beta-hairpins (beta 1 to beta 4). An approximately 50-amino acid segment that contains four short helices (alpha 2 to alpha 4), meanders around the surface of the core structure. In BRCA2, the alpha 9 and alpha 10 helices pack with the BRCA2 OB1 domain through van der Waals contacts involving hydrophobic and aromatic residues, and also through side-chain and backbone hydrogen bonds. This domain binds the 70-amino acid DSS1 (deleted in split-hand/split foot syndrome) protein, which was originally identified as one of three genes that map to a 1.5-Mb locus deleted in an inherited developmental malformation syndrome.