What question did this study set out to answer?

To investigate the kinetics of smooth-muscle caldesmon phosphorylation and evaluate how this modification alters its interaction with actin, calmodulin, and actomyosin Mg2+-ATPase activity.

June 1, 1987Biochemical JournalOpen Access

The effects of phosphorylation of smooth-muscle caldesmon

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Population

In vitro smooth muscle protein system

Comparison

Phosphorylation of caldesmon vs Unphosphorylated caldesmon

Design

Preclinical

Authors

PNP K NgaiKane Biotech (Canada)MWMichael P. WalshUniversity College Dublin

Discussion

Member takes

Implication

Suggests caldesmon phosphorylation regulates smooth muscle; leaves open relevance to human cardiovascular function.

Key Points

To investigate the kinetics of smooth-muscle caldesmon phosphorylation and evaluate how this modification alters its interaction with actin, calmodulin, and actomyosin Mg2+-ATPase activity.
Assessed in vitro phosphorylation kinetics of free and actin-, tropomyosin-, or thin-filament-bound caldesmon by endogenous Ca2+/calmodulin-dependent protein kinase.
Reconstituted actomyosin Mg2+-ATPase assays with actin, myosin, tropomyosin, calmodulin, and myosin light-chain kinase to compare the inhibitory actions of phosphorylated versus unphosphorylated caldesmon.
Measured actin-binding stoichiometry and calcium-dependent release of both caldesmon states in the presence of Ca2+/calmodulin.
Endogenous kinase rapidly phosphorylated caldesmon to approximately 1 mol of phosphate per mol of protein within 5 minutes in reconstituted systems.
Unphosphorylated caldesmon substantially inhibited actin-activated myosin Mg2+-ATPase, whereas phosphorylated caldesmon exerted no inhibitory effect whether modified prior to or during the ATPase reaction.
Caldesmon displayed maximal actin binding of 1:9.5 for unphosphorylated and 1:11.7 for phosphorylated forms, with Ca2+/calmodulin releasing 100% of phosphorylated caldesmon (half-maximal release at 0.11 µM Ca2+) versus 62% of unphosphorylated caldesmon (half-maximal release at 0.16 µM Ca2+).

Structured PICO

Population

In vitro smooth muscle protein system (caldesmon, actin, myosin, tropomyosin, calmodulin, myosin light-chain kinase)

Intervention

Phosphorylation of caldesmon

Comparator

Unphosphorylated caldesmon

Outcome

Actin-activated myosin Mg2+-ATPase activity and binding properties to actinsurrogate

Phosphorylation of smooth-muscle caldesmon prevents its inhibitory action on actomyosin Mg2+-ATPase, suggesting a regulatory mechanism for smooth muscle contraction.

Cite This Study

Ngai et al. (1987) studied this question.

synapsesocial.com/papers/6a7f31abfc226ad0a00dfbd2 https://doi.org/10.1042/bj2440417

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The effects of phosphorylation of smooth-muscle caldesmon

Discussion

Member takes

Implication

Key Points

Structured PICO

Cite This Study

The effects of phosphorylation of smooth-muscle caldesmon

Discussion

Member takes

Implication

Key Points

Structured PICO

Cite This Study

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