Phosphorylation of plant actin-depolymerising factor by calmodulin-like domain protein kinase

actin-depolymerising factor (ADF)/cofilin group of proteins are stimulus-re sponsive actin-severing proteins, members of which are regulated by reversi ble phosphorylation. The phosphorylation site on the maize ADF, ZmADF3, is Ser-6 but the kinase responsible is unknown [Smertenko et al,, Plant J. 14 (1998) 187-193]. We have partially purified the ADF kinase(s) and found it to be calcium-regulated and inhibited by N-(6-aminohesyl)-[H-3]5-chloro-1-n aphthalenesulphonamide. Immunoblotting reveals that calmodulin-like domain protein kinase(s) (CDPK) are enriched in the purified preparation and addit ion of anti-CDPK to in vitro phosphorylation assays results in the inhibiti on of ADF phosphorylation, These data strongly suggest that plant ADP is ph osphorylation by CDPK(s), a class of protein kinases unique to plants and p rotozoa. (C) 2001 Published by Elsevier Science B.V. on behalf of the Feder ation of European Biochemical Societies.