Figure 4. The loss of two hydrogen bonds as a result of the shift in the SXN motif contributes to disordering of the 74–90 region in Cys¹¹⁵-modified PBP 5.

In this stereo view, wild-type PBP 5 is represented by a grey backbone and side chains, whereas 2ME-modified PBP 5 is shown in orange. In wild-type PBP 5, there are two potential hydrogen bonds (shown as dashed lines) that link the SXN motif with the 74–90 region, which is fully ordered. In 2ME-modified PBP 5, these bonds are absent due to the shift in residues 106–111 induced by the 2ME alkylating Cys¹¹⁵, and their loss is hypothesized to lead to destabilization and disordering of the 74–90 loop. Residues that differ significantly in position between the two structures are coloured grey for wild-type and orange for 2ME-modified PBP 5. This Figure was prepared with MOLSCRIPT [47] and RASTER3D [48].