1,3,8-Trihydroxynaphthalene reductase (THNR)

1,3,8-Trihydroxynaphthalene reductase (THNR) is a short-chain dehydrogenase/reductase (SDR) enzyme essential for the biosynthesis of 1,8-dihydroxynaphthalene (DHN) melanin in certain fungal species, including the plant pathogen Magnaporthe grisea[1][3][5][6][7][8]. The enzyme catalyzes the reduction of 1,3,8-trihydroxynaphthalene to vermelone, an intermediate in the DHN-melanin pathway, and also reduces related substrates such as tetrahydroxynaphthalene to scytalone[8]. THNR is a validated target of several commercial fungicides (notably tricyclazole, pyroquilon, and phthalide), which act by inhibiting the enzyme, thereby blocking melanin synthesis and reducing fungal pathogenicity[1][3][5][6]. Structurally, THNR is a tetrameric protein containing a dinucleotide (NADPH)-binding fold, and its deep conservation among SDR enzymes provides a basis for structure-based inhibitor design[1][3][5]. Because of its central role in melanin biosynthesis and disease, THNR is considered a key molecular target for crop protection strategies against rice blast and similar fungal infections[1][4][5][6].

Other names

Trihydroxynaphthalene reductase1,3,8-THN reductase3HNRTetrahydroxynaphthalene reductase (used interchangeably in some literature, though technically distinct)

Inhibition of enzyme activity by binding the active site, preventing reduction steps in melanin biosynthesis