Phosphorylation of caldesmon by myosin light chain kinase increases its binding affinity for phosphorylated myosin filaments.

TitlePhosphorylation of caldesmon by myosin light chain kinase increases its binding affinity for phosphorylated myosin filaments.
Publication TypeJournal Article
Year of Publication2010
AuthorsSobieszek, A, Sarg, B, Lindner, H, Seow, CY
JournalBiol Chem
Volume391
Issue9
Pagination1091-104
Date Published2010 Sep
ISSN1437-4315
KeywordsAnimals, Binding Sites, Calmodulin-Binding Proteins, Muscle Contraction, Muscle, Smooth, Vascular, Myosin-Light-Chain Kinase, Myosins, Phosphoproteins, Phosphorylation, Protein Binding, Turkeys
Abstract

Phosphorylation of myosin by myosin light chain kinase (MLCK) is essential for smooth muscle contraction. In this study we show that caldesmon (CaD) is also phosphorylated in vitro by MLCK. The phosphorylation is calcium- and calmodulin (CaM)-dependent and requires a MLCK concentration close to that found in vivo. On average, approximately 2 mol P(i) per mol of CaD are incorporated at Thr-626 and Thr-693, with additional partial phosphorylation at Ser-658 and Ser-702. The phosphorylation rate for CaD is 20- to 50-fold slower than that for filamentous myosin; faster relative rates were obtained with CaD added to purified actomyosin or myosin preparations containing endogenous MLCK/CaM complex. Addition of CaM also augmented CaD phosphorylation. We further demonstrate that [³²P] labeled CaD binds much more readily to phosphorylated filamentous myosin than to unphosphorylated myosin. For actomyosin, CaD binding affinity doubles after myosin phosphorylation, without a significant change in binding stoichiometry (approx. one CaD per myosin molecule). Unphosphorylated CaD is ineffective in competing with the phosphorylated protein for the binding site(s) on myosin filaments. The ATPase activity of reconstituted actomyosin is inhibited by unphosphorylated CaD, and this inhibition was removed by CaD phosphorylation. Our results suggest that CaD phosphorylation plays a role in modifying actomyosin interaction in vivo, particularly during prolonged muscle activation.

DOI10.1515/BC.2010.105
Alternate JournalBiol. Chem.
PubMed ID20536391
Grant ListMT-13271 / / Canadian Institutes of Health Research / Canada