Modeling the three-dimensional structures of bacterial aminotransferases

The refined crystallographic structure of the "closed" conformation of chicken mitochondrial aspartate aminotransferase has been used as a template for the construction of models of the two Escherichia coli aminotransferases encoded by the tyrB and aspC genes. The main results are as follows: (1) Only minor changes are required in the coordinates of the backbone atoms to accommodate the large number of substituted side chains. (2) All deletions and insertions required to allow maximum primary sequence alignment are on the solvent-accessible surface. (3) Charged residues are all located on the surface, in contact with solvent, except for certain conserved active site residues. (4) The close packing within the hydrophobic core is maintained. (5) The interactions between the subunits are maintained. (6) Modeling of tyrosine as an external aldimine into the active sites points to several residues that could be involved in determining the substrate specificities of these aminotransferases.