PLANT PHYSIOLOGY , Vol 111, Issue 3 857-865, Copyright © 1996 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
A Calcium and Free Fatty Acid-Modulated Protein Kinase as Putative Effector of the Fusicoccin 14-3-3 Receptor
PCJ. Van der Hoeven, M. Siderius, HAAJ. Korthout, A. V. Drabkin and A. H. De Boer
Faculty of Biology, Department of Molecular and Cellular Biology, Vrije Universiteit Amsterdam, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands (P.C.J.V.d.H., H.A.A.J.K., A.H.D.B.)
A protein kinase that is activated by calcium and cis-unsaturated fatty
acids has been characterized from oat (Avena sativa L.) root plasma
membranes. The kinase phosphorylates a synthetic peptide with a motif
(-R-T-L-S-) that can be phosphorylated by both protein kinase C (PKC) and
calcium-dependent protein kinase (CDPK)-type kinases. Calphostin C and
chelerythrine, two PKC inhibitors, completely inhibited the kinase activity
with values of inhibitor concentration for 50% inhibition of 0.7 and 30
[mu]M, respectively. At low Ca2+ concentrations cis-unsaturated fatty acids
(linolenic acid, linoleic acid, arachidonic acid, and oleic acid)
stimulated the kinase activity almost 10-fold. The two inhibitors of the
kinase, calphostin C and chelerythrin, strongly reduced the fusicoccin
(FC)-induced H+ extrusion, and the activators of the kinase, the
cis-unsaturated fatty acids, prevented [3H]FC binding to the FC 14-3-3
receptor. CDPK antibodies cross-reacted with a 43-kD band in the plasma
membrane and in a purified FC receptor fraction. A polypeptide with the
same apparent molecular mass was recognized by a synthetic peptide that had
a sequence homologous to the annexin-like domain from barley 14-3-3. The
possibility of the involvement of a kinase, with properties from both CDPK
and PKC, and a phospholipase A2 in the FC signal transduction pathway is
discussed.
