Figure 7.

Trimerization of CcScsC. (a) Side view of the crystallographic trimer with the three protomer chains represented as surfaces and cartoons coloured orange, magenta and green. The trimer is approximately 80 Å in width. It is held together via interaction of the N-terminal α-helices (red box). (b) Close-up of the trimerization domain viewed from the side [red box in (a)] including electrostatic interactions between Asp8 and Lys14, Arg16 and Glu28, and Glu24 and Lys36. (c) Top view of the crystallographic trimer and (d) close-up of the inside of the trimerization domain [red box in (c)]. The interior of the trimer is lined with hydrophobic residues, including leucines (Leu19 and Leu26 are shown as sticks). The surface of each protomer is outlined in black, demonstrating the tight packing of the residues inside the helices. The positions of the active sites on the CcScsC C2S protomers are indicated with filled magenta circles. Models are shown as a combination of cartoon and surface representations and important residues are shown as sticks and labelled in (b) and (d). Electrostatic interactions are shown as dashed lines.