NSF-D1 and NSF-D2
Reproduced from [1].
Parallel versus antiparallel arrangement of NSF-D1 and NSF-D2. (A) 20Sm structure with 20Smtop in yellow and 20Smbot in blue. The arrow points in the direction of the rotational and translational fit carried out to compare 20Smtop with 20Smbot, and to determine the orientation of NSF-D1 with respect to NSF-D2. (B) Slice through 20Sm parallel to the symmetry axis. In the parallel arrangement of 20Smbot and 20Smtop, considerable density mismatch can be observed. The arrows point to density that does not overlap. Protrusions corresponding to the NSF-N domains are partially occupied. The inset shows a 2D projection of the difference map between 20Smbot and 20Smtop. Apart from the peaks in the region of the N domains, there are also strong peaks at the D1–D2 interface. In the antiparallel arrangement 20Smbot (blue) fits well into 20Smtop without major discrepancies between these two densities. For this arrangement, protrusions corresponding to the NSF-N domain remain unoccupied and are marked by an arrow. The difference map in the inset shows strong peaks in the region of the N domains, but not at the D1–D2 interface. (C) Fit of the NSF-D2 crystal structure into both 20Smbot and 20Smtop. The discrepancy seen between the parallel fit of the 20Smbot density into the 20Smtop density can also be seen between the NSF-D2 crystal structure and 20Smtop density. The arrows indicate density occupied in the antiparallel fit that is not occupied in the parallel fit. (D) Slice through 20Sm (yellow) at the interface between 20Smbot and 20Smtop, perpendicular to the symmetry axis. The position of the slice is marked by square brackets ] [ in (C). The NSF-D2 crystal structure fitted into the 20Smbot density is shown in light blue, and the NSF-D2 crystal structure fitted into the 20Smtop density is shown in dark blue or red for the antiparallel or parallel arrangement, respectively. The interface between 20Smbot and 20Smtop is well structured. For the antiparallel arrangement, almost the entire density is occupied and no significant discrepancies can be observed between the NSF-D2 crystal structure in 20Smbot and the NSF-D2 crystal structure in 20Smtop. The arrow points to a well-refined tube-like density that is likely to contain the N-terminus of NSF-D2 and/or the linker between NSF-D1 and NSF-D2. In the parallel arrangement, the NSF-D2 crystal structure does not fit well into 20Smtop at the interface between 20Smbot and 20Smtop. An α-helix of the NSF-D2 crystal structure that does not have a corresponding density in 20Sm is marked by a + sign. The arrows point to unoccupied density. (E) NSF-D2 crystal structures arranged in the parallel and antiparallel orientations.
