Crystal structure of NAD-dependent malate dehydrogenase complexed with NADP(H)

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• NAD-dependent malate dehydrogenase (tMDH) from Thermus flavus AT-62 plays a crucial role in cellular metabolism.
• Understanding coenzyme specificity is key to elucidating enzyme function and regulation.

Purpose of the Study:

• To investigate the coenzyme specificity of tMDH by determining the binding mode of NADP(H).
• To provide structural insights into the interaction between tMDH and its coenzymes.

Main Methods:

• X-ray crystallography was employed to determine the structure of the tMDH-NADP(H) complex at 1.65 Å resolution.
• Kinetic analysis was performed to study the malate-oxidizing reaction catalyzed by tMDH.

Main Results:

• The crystal structure revealed that NADP(H) binds to tMDH in a reverse orientation compared to NADH.
• Adenine of NADP(H) was observed near the catalytic center, while nicotinamide occupied the adenine binding site.
• Kinetic studies showed that NADP+ inhibits tMDH at high concentrations.

Conclusions:

• This study provides the first evidence for an alternative binding mode of nicotinamide coenzymes in a single enzyme.
• The findings highlight the flexibility of tMDH in accommodating different coenzyme forms.
• The observed binding mode has implications for understanding enzyme-coenzyme interactions and specificity.