Solution structure of the zinc finger domain of human RNF144A ubiquitin ligase

Dynamic regulation of Monascus azaphilones biosynthesis by the binary MrPigE-MrPigF oxidoreductase system

Monascus azaphilones (MAs) have been extensively applied as natural food coloring agents. MAs are classified into three categories: yellow MAs (YMAs), orange MAs (OMAs), and red MAs with various biological activities. However, the exact biosynthetic mechanism of OMAs and YMAs are not thoroughly elucidated. Firstly, we identified four DNA-binding residues of transcription factor MrPigB and constructed a multi-site saturation mutagenesis library of MrPigB. Then, comparative metabolite and gene expression of the mutants revealed that two oxidoreductases MrPigE and MrPigF were responsible for the formation of YMAs and OMAs. Finally, the in vitro and in vivo assays demonstrated the opposite roles of MrPigE and MrPigF in conversion of OMAs to YMAs. To our knowledge, this is the first report of a binary oxidoreductase system for dynamic regulation of fungal secondary metabolite biosynthesis. Broadly, our work also demonstrates the transcription factor engineering strategy for elucidating the biosynthetic pathway of secondary metabolite. KEY POINTS: • MrPigE converts orange Monascus azaphilones to yellow Monascus azaphilones • MrPigF oxidizes intermediates to afford orange Monascus azaphilones • MrPigE and MrPigF constitute a binary system in Monascus azaphilones biosynthesis.

Solution structure of the zinc finger domain of human RNF144A ubiquitin ligase

RNF144A is involved in protein ubiquitination and functions as an ubiquitin-protein ligase (E3) via its RING finger domain (RNF144A RING). RNF144A is associated with degradation of heat-shock protein family A member 2 (HSPA2), which leads to the suppression of breast cancer cell proliferation. In this study, the solution structure of RNF144A RING was determined using nuclear magnetic resonance. Moreover, using a metallochromic indicator, we spectrophotometrically determined the stoichiometry of zinc ions and elucidated that RNF144A RING binds two zinc atoms. This structural analysis provided the position and range of the active site of RNF144A RING at the atomic level, which contributes to the creation of artificial RING fingers having the specific ubiquitin-conjugating enzyme (E2)-binding capability.