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Updated: Aug 1, 2026

Defining Substrate Specificities for Lipase and Phospholipase Candidates
Published on: November 23, 2016
A structural account of substrate and inhibitor specificity differences between two naphthol reductases
D I Liao1, J E Thompson, S Fahnestock
1Experimental Station, DuPont Central Research and Development, Wilmington, Delaware 19880, USA. der-ing.liao@usa.dupont.com
Two fungal reductases, 4HNR and 3HNR, show distinct specificities for naphthol substrates and pyroquilon inhibitors. C-terminal residues in these enzymes determine these differences in fungal melanin biosynthesis.
Area of Science:
- Biochemistry
- Structural Biology
- Mycology
Background:
- Fungal melanin biosynthesis involves naphthol reduction reactions mediated by short chain dehydrogenase/reductases.
- 1,3,8-trihydroxynaphthalene reductase (3HNR) is targeted by the commercial fungicide pyroquilon.
Purpose of the Study:
- To determine the X-ray structure of 1,3,6,8-tetrahydroxynaphthalene reductase (4HNR) complexed with NADPH and pyroquilon.
- To compare the substrate and inhibitor specificities of 4HNR with 3HNR.
- To elucidate the structural basis for the differing specificities of these two enzymes.
Main Methods:
- X-ray crystallography of 4HNR-NADPH-pyroquilon complex at 1.5 A resolution.
- Comparative analysis with the 1.7 A resolution structure of 3HNR-NADPH-pyroquilon complex.
- Molecular modeling of substrates 1,3,8-trihydroxynaphthalene (3HN) and 1,3,6,8-tetrahydroxynaphthalene (4HN) in enzyme active sites.
Main Results:
- The sequences of 4HNR and 3HNR are 46% identical and share the same fold.
- 4HNR-NADPH complex shows 30-fold lower affinity for pyroquilon than 3HNR-NADPH complex due to unfavorable C-terminal interactions.
- Modeling explains the enzyme's preference for 4HN over 3HN and differences in substrate specificity based on C-terminal residue interactions.
Conclusions:
- C-terminal residues of 4HNR (Ile282) and 3HNR (Met283) are key determinants of both inhibitor and substrate specificities.
- Structural insights into naphthol reductases can inform fungicide development targeting fungal melanin biosynthesis.
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