Regulation of aflatoxin production by Ca super(2+)/calmodulin-dependent protein phosphorylation and dephosphorylation

• Published in: FEMS microbiology letters 2000-02, Vol.183 (2), p.215-219
• Main Author: Jayashree, T
• Format: Article
• Language: English
• Subjects: Aspergillus parasiticus; sodium lauryl sulfate
• ISSN: 0378-1097
• DOI: 10.1016/S0378-1097(99)00642-4

To elucidate Ca super(2+)-mediated regulation of aflatoxin production, the status of Ca super(2+)/calmodulin-dependent protein phosphorylation and dephosphorylation was investigated employing toxigenic and non-toxigenic strains of Aspergillus parasiticus. Incubation of cytoplasmic extracts with [ gamma - super(32)P]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 non-toxigenic strain (SRRC 255). Aflatoxin 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 Ca super(2+)/calmodulin-dependent protein kinase was susceptible to dose-dependent inhibition by aflatoxin. 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.