Biology Reference
In-Depth Information
4.19.3
Stimulation of CDPK Activity by 14-3-3 Proteins
14-3-3 proteins have been shown to modulate the activity of CPDK signal trans-
duction pathways. The 14-3-3 proteins are given this nomenclature based on their
chromatography and electroprofi les. The CDPK isoform CPK1 from
Arabidopsis
thaliana
is stimulated almost twofold by three different 14-3-3 proteins (Camoni
et al.
1998b
), suggesting that 14-3-3 proteins may modulate the activity of CDPK
signal transduction pathways in plants. Protein kinases and phosphatases are
regulated by 14-3-3 proteins (Ferl
2004
). 14-3-3 proteins specifi cally bind and
activate the
Arabidopsis thaliana
enzyme AtCPK1 in vitro in the presence of Ca
2+
(Camoni et al.
1998b
). The 14-3-3 proteins play a role in the completion of signal
transduction events. Phosphorylation may tag the proteins for association with
14-3-3 and the subsequent binding of 14-3-3s may complete the signal-induced
changes in the protein activity (Ferl
2004
). 14-3-3 proteins occur as homo- and
heterodimers in vitro and in vivo and these dimers may mediate interaction
between pairs of associated proteins (Jones et al.
1995
). It has been shown that
14-3-3 proteins bind to phosphorylated Ser residues present within one of a small
number of consensus sequences found in many of the proteins with which they
interact (Yaffe et al.
1997
).
4.19.4
Enhancement of CDPK Activity by Phospholipids
Specifi c phospholipids enhance in vitro substrate phosphorylation by CDPKs
(Farmer and Choi
1999
; Szczegielniak et al.
2000
). Certain phospholipids,
including phosphatidic acid, phosphatidylserine, and phosphatidylinositol, act as
second messengers and enhanced the CDPK activity (Farmer and Choi
1999
). In
the presence of Ca
2+
, specifi c phospholipids enhance phosphorylation by CDPKs
by 2-30 times above that observed with Ca
2+
alone (Harper et al.
1993
; Farmer and
Choi
1999
). Both phosphatidylinositol and lyso-phosphatidylcholine increase
substrate phosphorylation by CPK1 from
Arabidopsis
, while only phosphati-
dylinositol enhances the CDPK autophosphorylation (Binder et al.
1994
).
A binding site for phosphatidylinositol has been detected in the N terminus of
CPK1 (Binder et al.
1994
).
4.19.5
CDPKs Target Proteins Involved in Immune Signaling
System
CDPKs target several proteins involved in immune signaling systems (Fig.
4.8
).
CDPKs are involved in activation of various Ca
2+
-permeable channels in plant
cell plasma membrane. Arabidopsis CDPKs CPK6 and CPK3 have been shown
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