Transition State Stabilization

As is the case for lysozyme and the Cel5A glycosidase, there is significant distortion of the glucosyl unit containing the glycosidic bond to be cleaved.

Figure 1.  A comparison of maltose and the "maltose" unit in the enzyme substrate complex.

Figure 2. In the case of this glycosyltransferase, it is clear that the distortion is the result of tighter binding of the transition state (=distorted maltose ring).  The transition state is stabilized by two new hydrogen bonds between the sugar residue and His 140 and Arg 227.  These hydrogen bonds can only form if the sugar ring is distorted because in its undistorted conformation steric interaction of the sugar with Asp 328  prevents proper binding.