Structure-function relationships in human Class III alcohol dehydrogenase (formaldehyde dehydrogenase).

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Human Class III alcohol dehydrogenase (ADH), also known as glutathione-dependent formaldehyde dehydrogenase (FDH), is crucial for detoxifying formaldehyde and metabolizing S-nitrosoglutathione (GSNO).
• FDH exhibits a random bi-bi kinetic mechanism and a preference for bulkier substrates over smaller alcohols like ethanol.
• Understanding FDH's structure-function relationship is key to elucidating its catalytic mechanisms.

Purpose of the Study:

• To provide a structural basis for the observed kinetic properties of FDH.
• To investigate the structural changes in FDH upon coenzyme and substrate binding.
• To characterize the active site zinc coordination environment in different FDH states.

Main Methods:

• X-ray crystallography was used to determine the structures of FDH complexes, including the FDH.NAD(H) binary complex.
• Structural analysis focused on domain conformation, domain movements, and active site zinc coordination.
• Comparison of apoenzyme and complex structures provided insights into catalytic mechanisms.

Main Results:

• The apoenzyme displays a semi-open domain conformation, allowing for random substrate/coenzyme addition.
• No significant domain movement occurs upon binding of NAD(H) or the substrate 12-hydroxydodecanoic acid.
• Two distinct active site zinc coordination environments were observed: one in the apoenzyme and another in the FDH.NAD(H) complex, with a shift towards Glu67.

Conclusions:

• The structural data supports the kinetic observations of random substrate addition in FDH.
• The observed changes in zinc coordination upon NAD(H) binding may facilitate substrate exchange during catalysis.
• These findings enhance our understanding of FDH's enzymatic mechanism and its role in detoxification pathways.