Biomedical Engineering Reference
In-Depth Information
Tabl e 8. 1.
Regulatory proteins of contraction. Caldesmon can be sequestered away from actin by
calcium-calmodulin complexes; it is phosphorylated by PKC.
CMC
SMC
Troponin
Caldesmon
8.1.5
Caldesmon
Binding partners of caldesmon include actin, Ca
2
+
-calmodulin, myosin, tropo-
myosin, and phospholipids. Caldesmon also binds caltropin [
706
] and tubulin [
707
].
Alternatively spliced transcript variants generate diverse isoforms.
Caldesmon is implicated in the regulation of actomyosin interactions in smooth
myocytes as well as non-myocytes (Table
8.1
). Caldesmon precludes the ATPase
activity of myosin in smooth myocytes, in addition to the regulation of non-myocyte
contraction.
Caldesmon reversibly binds to
F
actin and actin-tropomyosin filaments. In
particular, the interaction of high-molecular-weight caldesmon
hMW
with actin-
tropomyosin filaments hinders myosin ATPase activity. Calmodulin binds to
caldesmon
hMW
at activating calcium concentrations, thereby hampering the
interaction of caldesmon
hMW
with actin-tropomyosin to activate the myosin ATPase
activity and cause contraction.
Mitogen-activated protein kinase that is regulated by protein kinase-C phospho-
rylates caldesmon, especially under smooth myocyte stretching [
708
].
8.1.6
Calponin
Calponin is a calcium- and calmodulin-binding protein that prevents the
Mg
AT P a s e
activity of myosin in smooth myocytes [
709
]. Calponin also connect to tropomyosin,
independently of Ca
2
+
, but links to calmodulin in the presence of Ca
2
+
ion
(Table
8.2
). Calponin is phosphorylated by protein kinase-C and Ca
2
+
-calmodulin-
dependent protein kinase CamK2 to relieve calponin inhibition of myosin.
8.2
Glycocalyx
Heparan sulfate proteoglycans of the glycocalyx (thickness 5-11
[
711
]), such
as syndecan-1 and -4, can cooperate with integrins to launch cell spreading and
assembly of focal adhesions and stress fibers.
In humans, calmodulin-like protein is a multifunctional calcium sensor that can regulate the Ca
2
+
-
induced Ca
2
+
release.
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