Divergent binding mode for a protozoan BRC repeat to RAD51

Interaction of BRCA2 through ca. 30 amino acid residue motifs, BRC repeats, with RAD51 is a conserved feature of the double-strand DNA break repair process in eukaryotes. In humans the binding of the eight BRC repeats is relatively well understood, with structure of BRC4 repeat bound to human RAD51 showing how two sequence motifs, FxxA and LFDE, in the BRC repeat interact with distinct sites on RAD51. Little is known however of the interaction of BRC repeats in other species, especially in protozoans where variable number of BRC repeats are found in BRCA2 proteins. Here we have studied in detail the interactions of the two BRC repeats in Leishmania infantum BRCA2 with RAD51. We show that the LiBRC1 is a high affinity repeat with a KD of 0.29 M while LiBRC2 binds to RAD51 with a KD of 13.5 M. A crystal structure of LiBRC1 complexed with LiRAD51 revels an extended {beta}-hairpin compared to human BRC4 and shows that the equivalent of human LFDE motif is not interacting with LiRAD51. A truncation analysis of LiBRC1 confirms that a shorter repeat is sufficient for high affinity interaction and this minimal repeat is functional in inhibiting the formation of LiRAD51-ssDNA nucleofilament.