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Contenuto archiviato il 2022-12-23

Regulation of smooth muscle thin filaments by caldesmon phosphorylation

Obiettivo

Smooth muscle contractility is controlled by regulatory proteins associated with the myosin and acting filaments. Whilst activation of myosin by Ca2+ dependent phosphorylation is the primary regulator in all smooth muscles, tonic smooth muscles (e.g. vascular smooth muscle, airway smooth muscle) are also regulated by the 'chemoreceptor' pathway, which involves cell signalling kinases and phosphorylation of target nuclear and cytoplasmic proteins. Caldesmon is the regulatory protein of the thin filaments; it inhibits contractile activity and it is regulated by Ca2+-calmodulin and also by phosphorylation. The Moscow laboratory has recently established that at least 90% of caldesmon phosphorylation in vivo is due to MAP kinase. In mammalian caldesmon there are three potential MAP kinase sites: Thr730, Ser759 and Ser799 (absent in chicken). Whilst much investigation has been concentrated on the effects of Ser759 phosphorylation, recent results form the Moscow lab indicate that in vivo the predominant site of phosporylation in PdBu-stimulated arterial smooth muscle is probably Thr730, however there may be more additional N-terminal sites.
It is proposed to study the physiological, functional and structural consequences of caldesmon phosphorylation. The initial task of this study will be to determine accurately the in vivo phosphorylation sites of caldesmon under physiological stimulation.

The assignment of sites will be confirmed by phosphorylating deletion mutants of caldesmon containing just one of the identified sites with MAP kinase in vitro. It is then planned to develop a phosphospecific antibody to each site to monitor intracellular interactions of caldesmon and the level of agonist-stimulated phosphorylation of caldesmon. This will be used to explore the contribution of site-specific phosphorylation in regulation of smooth muscle contraction/relaxation by caldesmon.
The functional effects of Thr730 phosphorylation on actomyosin interaction will be investigated in vitro by ATPase and in vitro motility assays using well-characterised deletion mutants of caldesmon. Specific phosphorylation will be achieved by making Ser/Thr>Ala point mutants. It is expected that phosphorylation will reduce inhibitory function and interaction with Ca2+-calmodulin and that this will primarily affect the cooperativity of the regulated thin filament. The effects of phosphorylation on the structure of caldesmon domain 4 will be determined by high-resolution protein NMR and the effect on caldesmon-actin interaction will be studied by heteronuclear NMR, SPR and by the unique method of Dr Borovikov, which detects conformational changes in actin molecules in ghost fibres, which have an intact actin filament lattice. The functional effects of caldesmon phosphorylation on contractility in a more physiological system will be tested in chemically skinned smooth muscle fibres by replacing native caldesmon with recombinant caldesmon deletion mutants and specifically phosphorylated caldesmon mutants.

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Coordinatore

Imperial College of Science Technology and Medicine
Contributo UE
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Indirizzo
Dovehouse Street
N6 6NT London
Regno Unito

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