Resolving the fungal velvet domain architecture by Aspergillus nidulans VelB.

Velvet transcription factors are found throughout the fungal kingdom and share a common velvet domain with a fold similar to that of animal NF-κB. They act as homodimeric or heterodimeric master regulators of fungal secondary metabolism, development, and differentiation. A comparison of velvet domains from 4,999 fungal velvet proteins revealed a conserved overall architecture, including an N-terminal DNA-binding region of approximately 30 amino acids and a C-terminal dimerization region of about 100 amino acids. The dimerization region comprises α- and β-subunits separated by a linker region. A detailed analysis of the velvet domain in Aspergillus nidulans VelB identified glycine (glycine 240) and leucine (leucine 331) residues in the dimerization region as critical for interactions with velvet proteins. These core amino acid residues are conserved and also essential for the function of VeA or VosA, which corroborates their general importance in functional fungal velvet domains. Functional studies of VelB dimerization linkers suggest its tolerance for length shortening. These findings enhance our understanding of the working mechanisms of fungal velvet regulators.IMPORTANCEFungi, as relatives of animals within Opisthokonta, are closely connected to human life through interactions such as food, pathogenicity, and medicines. Similar to animals, fungi have developed NF-κB-like velvet family regulators to respond to various environmental and internal signals. Velvet regulators form homo- or heterodimers in implementing different functional roles. However, the molecular mechanism by which velvet proteins interact remains incompletely understood. In this study, we found a common architecture of fungal velvet domains and resolved the dimerization region using Aspergillus nidulans VelB as a paradigm. The growing understanding of the fungal velvet regulatory network may help to control fungi for pathogenic and industrial purposes and shed light on the general mechanisms shared with the animal NF-κB system in cellular responses to stimuli.