Members of this family assume an OB fold, which consists of a highly curved five-stranded beta-sheet that closes on itself to form a beta-barrel. OB3 has a pronounced groove formed by one face of the curved sheet and is demarcated by two loops, one between beta 1 and beta 2 and another between beta 4 and beta 5, which allows for strong ssDNA binding [1].

1: BRCA2 function in DNA binding and recombination from a BRCA2-DSS1-ssDNA structure. Yang H, Jeffrey PD, Miller J, Kinnucan E, Sun Y, Thoma NH, Zheng N, Chen PL, Lee WH, Pavletich NP; Science 2002;297:1837-1848. PMID:12228710