Putative calmodulin-binding domains in aflatoxin biosynthesis-regulatory proteins.

The inhibition of aflatoxin production by trifluoperazine, an anticalmodulin (CaM) agent and the relevance of Ca(2+)/CaM-dependent phosphorylation and dephosphorylation during aflatoxin biosynthesis was previously reported. To identify proteins that may be regulated by CaM, an in silico analysis for putative CaM-binding domains (CaMBDs) in the aflatoxin-related proteins of Aspergillus parasiticus was performed using the CaM target database. Interestingly, the key regulators of aflatoxin biosynthesis such as AflR and AflJ contained predicted CaMBDs at their C-termini. Furthermore, potential phosphorylation sites for CaM-kinase II were present within these CaMBDs. In addition to other aflatoxin biosynthesis enzymes--such as Vbs, DmtA and OmtA, and the VeA protein (known to regulate the expression of AflJ and AflR)--also showed the presence of putative CaMBDs. Although the present report reaffirms earlier observations on CaM-mediated regulation of aflatoxin biosynthesis, it also opens new avenues for identifying the specific targets of CaM and elucidating the exact mechanism of initiation and regulation of aflatoxin biosynthesis.