Figure 9
Difference density at the BAFF disulfide between residues 232 and 245. The pictures are for the B chain, but the other NCS copies are similar. (a) BUSTER refinement of 1osg with TLS and NCS produces an 8σ negative difference density peak. (b) A much better fit to density is found by modelling partial disulfide-bond formation using two alternates for the Cys232 and Cys245 SG atoms. Shown in yellow is alternate `A' with a disulfide bond between the atoms. The alternate `B' marked in orange has the S atoms in a reduced form. A bound water molecule that forms three good hydrogen-bond contacts can be placed nearby. The 2Fo − Fc density is contoured at 1.2σ and the Fo − Fc difference density at 3.5σ. |