1TOE: Unliganded Structure Of Hexamutant + A293d Mutant Of E. Coli Aspartate Aminotransferase

Several mutant Escherichia coli aspartate aminotransferases (eAATases) have been characterized in the attempt to evolve or rationally redesign the substrate specificity of eAATase into that of E. coli tyrosine aminotransferase (eTATase). These include HEX (designed), HEX + A293D (design followed by directed evolution), and SRHEPT (directed evolution). The A293D mutation realized from directed evolution of HEX is here imported into the SRHEPT platform by site-directed mutagenesis, resulting in an enzyme (SRHEPT + A293D) with nearly the same ratio of k(cat)/K(m)(Phe) to k(cat)/K(m)(Asp) as that of wild-type eTATase. The A293D substitution is an important specificity determinant; it selectively disfavors interactions with dicarboxylic substrates and inhibitors compared to aromatic ones. Context dependence analysis is generalized to provide quantitative comparisons of a common substitution in two or more different protein scaffolds. High-resolution crystal structures of ligand complexes of HEX + A293D, SRHEPT, and SRHEPT + A293D were determined. We find that in both SRHEPT + A293D and HEX + A293D, the additional mutation holds the Arg 292 side chain away from the active site to allow increased specificity for phenylalanine over aspartate. The resulting movement of Arg 292 allows greater flexibility of the small domain in HEX + A293D. While HEX is always in the closed conformation, HEX + A293D is observed in both the closed and a novel open conformation, allowing for more rapid product release.
PDB ID: 1TOEDownload
MMDB ID: 29456
PDB Deposition Date: 2004/6/14
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 1TOE: dimeric; determined by author and by software (PISA,PQS)
Molecular Components in 1TOE
Label Count Molecule
Proteins (2 molecules)
Aspartate Aminotransferase(Gene symbol: aspC)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB