Fig. 3
Comparison of open and closed conformation of PrBP/δ. a Apo-PrBP/δ in “open” conformation. Apo-PrBP/δ in open conformation is shown as ribbon representation with a cavity-surface (cyan/orange). A β-sheet extension is formed due to β-strand 6 interaction based on the crystallographic interface of apo-PrBP/δ (orange) with N-terminus of the symmetry related apo-PrBP/δ molecule (cyan). b PrBP/δ in “closed” conformation. In the crystal structure complex of PrBP/δ with its displacement factor Arl2 a very similar β-sheet extension is formed in which the β-strand 6 of PrBP/δ (green) interacts with β2 strand of Arl2 (purple). Phe50 of Arl2 (highlighted in pink) (c) seems to induce a rotameric shift of Phe94 in PrBP/δ. For both apo-PrBP/δ (“open” conformation) and Arl2-bound PrBP/δ (“closed” conformation) this extension of the β-sheet with β6 is observed. c Superposition of the apo-PrBP/δ in “open” (orange) and PrBP/δ-Arl2-bound in closed (green) conformation. Closure of the PrBP/δ cavity is apparently induced by the Phe50 of Arl2 that might induce a cascade of side chain shifts of several residues such as Phe94, Trp105 and Arg61. These shifts allow formation of a new hydrogen bonding network including the residues Arg61, Gln78, Glu88, and Trp90 in the “close” conformation that are additionally responsible for the size reduction of the cavity. In contrast the distance between Arg61 and Glu88 is ~10 Å in the “open” conformation of apo-PrBP/δ
