   4.3.1.1 | in an unliganded state and in complex with L-aspartate at 2.4 and 2.6 A resolution, respectively. AspB forces the bound substrate to adopt a high-energy, enediolate-like conformation that is stabilized, in part, by an extensive network of hydrogen bonds between residues Thr101, Ser140, Thr141, and Ser319 and the substrate's beta-carboxylate group. Substrate binding induces a large conformational change in the SS loop, residuesG317SSIMPGKVN326, from an open conformation to one that closes over the active site. In the closed conformation, the strictly conserved SS loop residue Ser318 is at a suitable position to act as a catalytic base, abstracting the Cbeta proton of the substrate in the first step of the reaction mechanism. The small C-terminal domain of AspB plays an important role in controlling the conformation of the SS loop |
