However, after a 3-ns molecular dynamics simulation, all the residues in our model were in the ''core'' and ''allowed'' regions. It can be seen from Fig. 2A that, like most of the other metallo-blactamases, the NDM-1 protein belongs to the a/b structural class [54] , with 3 helices and 7 b-strands. The 3 helices were exposed to the solvent. The N-terminal and C-terminal regions of NDM-1 can be superposed by a 180 degrees rotation around a central axis, indicating that the entire structure may have arisen from the duplication of a gene. It was found after superposing NDM-1 to its template structure 1ko3.pdb that the two structures share a quite similar backbone (Fig. 2B ) owe to their high sequence identity percentage. However, some a-helices and b-strands in 1ko3.pdb are not seen in the NDM-1 model because 1ko3.pdb contains 5 helices and 11 b-strands. This is due to the sequence deletion of NDM-1 in its C-terminal and N-terminal regions. It is instructive to note that such sequence deletion might make the b-lactam antibiotic drugs easier to access the binding pocket of NDM-1.