The structure of BCh12 and its crystal packing interactions. (A) Stereodiagram of the structure of BCh12, secondary structure of the turn region shown on the left. Blue: the S (shorter) strand of a monomer. Purple: the L (longer) strand that forms a helix with the blue S strand. Green: the portion of the L strand of the neighboring monomer that forms a double helix with the L1–L6 region of the purple stand (see Fig. 1). (B) A global view of the unit cell in the BCh12 crystal, with monomers shown in different colors to aid in distinguishing them. (C) The blunt end stacking contact that aligns successive BCh12 dimers in the crystal along the crystallographic b-axis, and the S12–L14 contact that fixes the relative positions of parallel dimers in the c-axis direction. (D) The interaction between the adjacent dimer helices that positions neighbors in the a-axis direction.
