Temperature dependence of the enzyme-substrate recognition mechanism

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Hyperthermophilic enzymes offer unique insights into protein stability and function at extreme temperatures.
• Alpha-aminotransferases are crucial enzymes involved in amino acid metabolism.
• Understanding enzyme dynamics is key to protein engineering and drug discovery.

Purpose of the Study:

• To determine the crystal structure of liganded alpha-aminotransferase from the hyperthermophile Pyrococcus horikoshii.
• To investigate the enzyme's domain movement upon binding of an acidic substrate, glutamate.
• To compare the structural dynamics with homologous enzymes from mesophilic and moderately thermophilic organisms.

Main Methods:

• X-ray crystallography was employed to determine the three-dimensional structure of the enzyme-substrate complex.
• Structural analysis focused on domain orientation and flexibility upon ligand binding.
• Comparative structural analysis was performed with related enzymes from Thermus thermophilus and Escherichia coli.

Main Results:

• The crystal structure of liganded Pyrococcus horikoshii alpha-aminotransferase showed minimal domain movement, primarily a small alpha-helical shift.
• The omega-carboxyl group of glutamate was recognized by Tyr70 without side-chain movement.
• Enzymes with higher thermophilicity exhibited progressively smaller domain movements upon substrate binding.

Conclusions:

• The study reveals a correlation between increased thermophilicity and reduced domain flexibility in alpha-aminotransferases.
• This principle of reduced domain movement in thermophilic enzymes may be a general phenomenon applicable to other enzyme families.
• The findings provide valuable structural insights for designing thermostable enzymes.