Active site loop difference
that relates to the presence of Asp257
in DHQS vs Asn270 in ValA. Shown are residues 269–278 of ValA
(purple) and residues 256–264 of DHQS (cyan, PDB entry 1DQS) after the proteins
have been overlaid as in Figure 5. H-Bonding
interactions (dashed lines) involving the loop residues and associated
waters are shown. In DHQS, the Asp257 carboxylate receives H-bonds
directly or indirectly (via water) from four backbone nitrogens (from
Arg259, Gly261, Gly262, and Arg264). In ValA, the Asn270 side chain
amide directly or indirectly makes H-bonds with two backbone nitrogens
(from Trp272 and Glu275) and two backbone oxygens (from Gln275 and
Arg277).