|French, Alfred - Al|
Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2009
Publication Date: 8/14/2009
Citation: Johnson, G.P., Peterson, L., French, A.D., Reilly, P. 2009. Twisting of glycosidic bonds by hydrolases. Carbohydrate Research. 344:2157-2166. Interpretive Summary: Understanding the mechanisms used by enzymes to break long carbohydrate molecules into their building blocks should be useful in designing new, more efficient enzymes. One feature of these breakage reactions is distortion of the ring structures of these building blocks. Another possible distortion is of the linkages between the different building blocks. That question was examined in this paper. Experimentally determined geometries of the linkages between the building blocks were compared with calculated energies from a modeling study. Some linkages were indeed found to be distorted at the location where the long molecules are broken. This work should be useful to those studying enzymes for breaking down carbohydrates, including cellulose and starch.
Technical Abstract: Patterns of scissile bond twisting have been found in crystal structures of glycoside hydrolases (GHs) that are complexed with substrates and inhibitors. To estimate the increased potential energy in the substrates that results from this twisting, we have plotted torsion angles for the scissile bonds on hybrid Quantum Mechanics::Molecular Mechanics energy surfaces. Eight such maps were constructed, including one for -maltose and three for different forms of methyl - acarviosinide to provide energies for twisting of -(1,4) glycosidic bonds. Maps were also made for -thiocellobiose and for three -cellobiose conformers having different glycon ring shapes to model distortions of -(1,4) glycosidic bonds. Different GH families twist scissile glycosidic bonds differently, increasing their potential energies from 0.5 to 9.5 kcal/mol. In general, the direction of twisting of the glycosidic bond away from the conformation of lowest intramolecular energy correlates with the position (syn or anti) of the proton donor with respect to the glycon’s ring oxygen atom. That correlation suggests that glycosidic bond distortion is important for the optimal orientation of one of the glycosidic oxygen lone pairs toward the enzyme’s proton donor.