Dihydrodipicolinate synthase from Thermotoga maritima

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Dihydrodipicolinate synthase (DHDPS) is a key enzyme in the lysine biosynthesis pathway in bacteria and plants.
• This pathway is essential for producing lysine, an amino acid vital for protein synthesis.
• DHDPS is typically feedback inhibited by lysine, regulating its own production.

Purpose of the Study:

• To investigate the structural and functional properties of DHDPS from the thermophilic bacterium Thermotoga maritima.
• To understand the basis for its enhanced stability compared to mesophilic counterparts.
• To explore its feedback inhibition characteristics.

Main Methods:

• Enzyme activity assays at high temperatures and in denaturing conditions (urea).
• Sedimentation analysis to determine quaternary structure.
• Comparison of active site and subunit interface residues with Escherichia coli DHDPS.

Main Results:

• Thermotoga maritima DHDPS demonstrated exceptional stability, retaining activity after incubation at 90°C or in 8 M urea.
• The enzyme exists as a tetramer with a molar mass of 133 kDa.
• Structural differences at the subunit interface, including cysteine residues forming a disulfide bond, contribute to its stability.
• Unlike E. coli DHDPS, the thermophilic enzyme was not inhibited by (S)-lysine.

Conclusions:

• The enhanced heat and chemical stability of T. maritima DHDPS is attributed to increased inter-subunit contacts and potentially disulfide bond formation.
• The lack of lysine feedback inhibition suggests that this regulatory mechanism evolved later in the bacterial lineage.
• These findings provide insights into enzyme adaptation to extreme environments and the evolution of metabolic pathways.