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Figure 9.
Fig. 9. Superposition of BmorPBP1 (PDB code 1DQE) and
BmorGOBP2 to show structural differences. (a) A stereo pair of
BmorPBP1 (red), BmorGOBP2 (blue with regions of greatest
difference in light blue). The disulfide bonds are yellow. The
bombykol ligand is represented as cylinders and coloured light
blue for the BmorGOBP2-bound conformation and pink for the
BmorPBP1-bound conformation. The ligand hydrogen bonding
residues Ser56 for BmorPBP1 and Arg110 for BmorGOBP2 are shown
as green cylinders. (b) (i) Enlarged and simplified view of the
major structural difference in the rear entry region (C-termini
from residue 126 and residues 25-49). Features are coloured as
described above. A potentially important stabilising hydrogen
bonding network has been included for BmorPBP1 (Tyr41 and Glu32,
shown as pink cylinders). The equivalent Phe41 in BmorGOBP2
(shown as blue cylinders) is buried more deeply and occupies the
space of the helix in BmorPBP1. The equivalent region of
BmorGOBP2 bulges out to occupy the space filled by the
C-terminus of BmorPBP1. (ii) Cut-away view of the ligand-binding
pocket showing the key hydrogen bonds formed with the bombykol
hydroxyl. PBP1 in red/pink and GOBP2 in blue. Hydrogen bonding
side chains are in green. (c) A representation of the possible
hydrogen bonding modes of bombykol and bombykal with hydrogen
bonds shown as dotted lines. (i) The hydroxyl of bombykol able
to form hydrogen bonds to water and to Glu98; and (ii) the
aldehyde of bombykal able to form only a single hydrogen bond to
water.
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