2A6N: Dihydrodipicolinate Synthase (e. Coli)- Mutant R138a

In plants and bacteria, the branch point of (S)-lysine biosynthesis is the condensation of (S)-aspartate-beta-semialdehyde [(S)-ASA] and pyruvate, a reaction catalyzed by dihydrodipicolinate synthase (DHDPS, EC It has been proposed that Arg138, a residue situated at the entrance to the active site of DHDPS, is responsible for binding the carboxyl of (S)-ASA and may additionally be involved in the mechanism of (S)-lysine inhibition. This study tests these assertions by mutation of Arg138 to both histidine and alanine. Following purification, DHDPS-R138H and DHDPS-R138A each showed severely compromised activity (approximately 0.1% that of the wild type), and the apparent Michaelis-Menten constant for (S)-ASA in each mutant, calculated using a pseudo-single substrate analysis, was significantly higher than that of the wild type. This provides good evidence that Arg138 is indeed essential for catalysis and plays a key role in substrate binding. To test whether structural changes could account for the change in kinetic behavior, the solution structure was probed via far-UV circular dichroism, confirming that the mutations at position 138 did not modify secondary structure. The crystal structures of both mutant enzymes were determined, confirming the presence of the mutations and suggesting that Arg138 plays an important role in catalysis: the stabilization of the catalytic triad residues, a motif we have previously demonstrated to be essential for activity. In addition, the role of Arg138 in (S)-lysine inhibition was examined. Both mutant enzymes showed the same IC(50) values as the wild type but different partial inhibition patterns, from which it is concluded that arginine 138 is not essential for (S)-lysine inhibition.
PDB ID: 2A6NDownload
MMDB ID: 35578
PDB Deposition Date: 2005/7/3
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.94  Å
Source Organism:
Similar Structures:
Biological Unit for 2A6N: tetrameric; determined by author
Molecular Components in 2A6N
Label Count Molecule
Proteins (4 molecules)
Dihydrodipicolinate Synthase(Gene symbol: dapA)
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB