Regulation of aflatoxin production by Ca2+/calmodulin-dependent protein phosphorylation and dephosphorylation

To elucidate Ca2--mediated regulation of anatoxin production, the status of Ca2+/calmodulin-dependent protein phosphorylation and dephosphorylation was investigated employing toxigenic and non-toxigenic strains of Aspergillus parasiticus. Incubation of cytoplasmic extracts with [gamma-P-32]ATP followed by SDS-PAGE and autoradiography revealed total absence of protein phosphorylation during periods corresponding to aflatoxin production in the toxigenic strain (NRRL 2999). In contrast, protein phosphorylation was unaffected in the nontoxigenic strain (SRRC 255). Anatoxin production in the toxigenic strain was also accompanied by enhanced (26-fold) activity of calcineurin (calmodulin-dependent protein phosphatase 2B) concomitant with a lowered (6-fold) activity of calmodulin-dependent protein kinase. In addition, the in vitro activity of Ca2+/calmodulin-dependent protein kinase was susceptible to dose-dependent inhibition by anatoxin. Since calcineurin remains active in the absence of phosphorylation by calmodulin-dependent protein kinase, it is suggested that calcineurin-mediated dephosphorylation of regulatory enzymes ensures continued production of aflatoxins. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.