Details

Autor(en) / Beteiligte

• Füller, Janis J.
• Röpke, René
• Krausze, Joern
• Rennhack, Kim E.
• Daniel, Nils P.
• Blankenfeldt, Wulf
• Schulz, Stefan
• Jahn, Dieter
• Moser, Jürgen

Titel

Biosynthesis of Violacein, Structure and Function of l-Tryptophan Oxidase VioA from Chromobacterium violaceum

Ist Teil von

• The Journal of biological chemistry, 2016-09, Vol.291 (38), p.20068-20084

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2016

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• Violacein is a natural purple pigment of Chromobacterium violaceum with potential medical applications as antimicrobial, antiviral, and anticancer drugs. The initial step of violacein biosynthesis is the oxidative conversion of l-tryptophan into the corresponding α-imine catalyzed by the flavoenzyme l-tryptophan oxidase (VioA). A substrate-related (3-(1H-indol-3-yl)-2-methylpropanoic acid) and a product-related (2-(1H-indol-3-ylmethyl)prop-2-enoic acid) competitive VioA inhibitor was synthesized for subsequent kinetic and x-ray crystallographic investigations. Structures of the binary VioA·FADH2 and of the ternary VioA·FADH2·2-(1H-indol-3-ylmethyl)prop-2-enoic acid complex were resolved. VioA forms a “loosely associated” homodimer as indicated by small-angle x-ray scattering experiments. VioA belongs to the glutathione reductase family 2 of FAD-dependent oxidoreductases according to the structurally conserved cofactor binding domain. The substrate-binding domain of VioA is mainly responsible for the specific recognition of l-tryptophan. Other canonical amino acids were efficiently discriminated with a minor conversion of l-phenylalanine. Furthermore, 7-aza-tryptophan, 1-methyl-tryptophan, 5-methyl-tryptophan, and 5-fluoro-tryptophan were efficient substrates of VioA. The ternary product-related VioA structure indicated involvement of protein domain movement during enzyme catalysis. Extensive structure-based mutagenesis in combination with enzyme kinetics (using l-tryptophan and substrate analogs) identified Arg64, Lys269, and Tyr309 as key catalytic residues of VioA. An increased enzyme activity of protein variant H163A in the presence of l-phenylalanine indicated a functional role of His163 in substrate binding. The combined structural and mutational analyses lead to the detailed understanding of VioA substrate recognition. Related strategies for the in vivo synthesis of novel violacein derivatives are discussed.