Aldo-keto reductases 7A subfamily: A mini review

Aldo-keto reductase-7A (AKR7A) subfamily belongs to the AKR superfamily and is associated with detoxification of aldehydes and ketones by reducing them to the corresponding alcohols. So far five members of ARK7A subfamily are identified: two human members-AKR7A2 and AKR7A3, two rat members-AKR7A1 and AKR7A4, and one mouse member-AKR7A5, which are implicated in several diseases including neurodegenerative diseases and cancer. AKR7A members share similar crystal structures and protein functional domains, but have different substrate specificity, inducibility and biological functions. This review will summarize the research progress of AKR7A members in substrate specificity, tissue distribution, inducibility, crystal structure and biological function. The significance of AKR7A members in the occurrence and development of diseases will also be discussed.

Trp266 determines the binding specificity of a porcine aflatoxin B₁ aldehyde reductase for aflatoxin B₁-dialdehyde

Aflatoxin B₁ (AFB₁) is a severe threat to human and animal health. The aflatoxin B₁ aldehyde reductase (AFAR) family specifically catalyzes AFB₁-dialdehyde, a toxic metabolic intermediate of AFB₁, producing a nontoxic dialcohol. Although several AFARs have been found and characterized, the binding specificity of the family for AFB₁-dialdehyde remains unclear. Herein, according to the published sequence, we cloned a porcine AFAR gene. Recombinant porcine AFAR was expressed and purified from Escherichia coli as hexa-histidine tagged fusion protein. Using the cloned porcine AFAR as a model, site-directed mutagenesis combined with high performance liquid chromatography studies revealed that the substitution of Trp266 with Ala resulted in almost complete loss of catalytic activity for AFB₁-dialdehyde. Interestingly, the substitution of Met86 with Ala exhibited an obviously increased activity to the dialdehyde. Based on these results and by using molecular docking simulations, this work provides a structural explanation for why the AFAR family exhibits high specificity for AFB₁-dialdehyde. The Trp266 residue in porcine AFAR plays a critical role in stabilizing the binding of AFB₁-dialdehyde in the active pocket through the hydrophobic interaction of the side-chain indole ring of Trp266 with the fused coumarin rings of the dialdehyde molecule. The enhanced activity of M86A may be attributed to the formed π-π stacking interaction between Trp266 and the dialdehyde. In addition, other hydrophobic residues (e.g. Phe and Trp) around the dialdehyde molecule also stabilize the substrate binding. The findings may contribute to understanding the substrate specificity of the AFAR family for AFB₁-dialdehyde.