Biology Reference
In-Depth Information
4.15
Calmodulin-Like Proteins as Ca
2+
Sensors
Some CaM-like proteins are also involved in calcium signaling system. Typical
CaMs are highly similar to animal CaM, whereas CaM-like proteins share 50-75 %
identity to typical CaM and have CaM activity. A calmodulin-like protein, Hra32,
involved in defense response has been detected in bean. The predicted Hra32 prod-
uct contains four putative EF-hand calcium-binding domains that are separated by a
spacing of nine amino acids (Jakobek et al.
1999
).
Arabidopsis
CaM8 is a CaM-like
protein. This protein can function as a CaM in Ca
2+
binding, but it appears to interact
with a more limited set of target proteins compared with typical CaM isoforms
(Zielinski
2002
).
A tomato gene (
APR34
) encoding a CaM -like protein has been characterized.
APR134
-like genes (
CML42
and
CML43
) have been isolated from Arabidopsis.
The
CML43
gene was rapidly induced in disease-resistant
Arabidopsis
leaves.
Overexpression of
CML43
in
Arabidopsis
accelerated the hypersensitive response
(Chiasson et al.
2005
), suggesting the role of the CAM-like protein in plant immune
response.
Centrins are CaM-like proteins with four Ca
2+
-binding EF-hand motifs
(Lecourieux et al.
2006
). Centrins have been found to be associated with cytoskel-
eton and a role in microtubule severing and cytoskeleton reorganization has been
shown (Lecourieux et al.
2006
). Arrangement of microtubules and microfi laments
was found to play an important role in the expression of nonhost resistance in barley
(Kobayashi et al.
1997
). A rapid and Ca
2+
-dependent disruption of microtubular
cytoskeleton is associated with disease resistance-associated cell death in a fungal
elicitor-treated tobacco cells (Binet et al.
2001
).
CCD-1
mRNA accumulates rapidly
in elicitor-treated wheat cells (Takezawa
2000
).
CCD-1
encodes a 14-kDa Ca
2+
-
binding protein that shares homology with the C-terminal half domain of centrin
(Takezawa
2000
). These studies showed that centrins are involved in disease resis-
tance responses and in Ca
2+
signaling.
Some CaM proteins have additional non-CaM domains and they are called CaM-
related proteins (Luan et al.
2002
). Petunia CaM53 is a CaM-related protein. It has
CaM activity but it contains a polybasic C-terminal domain that is not found in typi-
cal CaMs. This extra domain in CaM53 regulates the cellular localization
(Rodriguez-Concepcion et al.
1999
).
4.16
Calcineurin B-Like Proteins as Ca
2+
Sensors
Another family of Ca
2+
sensors consists of proteins similar to both the regulatory
B-subunit of calcineurin and the neuronal Ca
2+
sensor in animals and these Ca
2+
sensors are called calcineurin B-like (CBL) proteins (Luan et al.
2002
; Batisti
ć
et al.
2008
; Hashimoto et al.
2012
). Calcineurin is a Ca
2+
/calmodulin-dependent
protein phosphatase belonging to PP2B type (Kudla et al.
1999
; Trewavas
1999
).
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