Close contacts between the hydroxyethyl group and Asn132 and/or DW were also observed in our simulations. In carbapenemases, the Asn132 side chain can form a hydrogen bond to the carbapenem hydroxyethyl group, keeping it in the (carbapenemase-specific) Position II. The importance of avoiding steric clashes involving the hydroxyethyl group was suggested by investigations of the TEM-1 Asn132Ala mutant (PDB ID 1JVJ ). Removal of the Asn132 side chain led to less strained interactions within the carbapenem binding site and a different orientation of bound imipenem with respect to the oxyanion hole (with the carbonyl oxygen pointing into the oxyanion hole, as opposed its position in the X-ray structure of the complex with wild-type enzyme ). Positional shifts of Asn132 observed in various crystal structures, as well as the simulations performed here of the Asn132Gly substitution in BlaC, support the importance of residue 132, which indirectly influences reaction barriers .