A molecular model of phosphorylation-based activation and potentiation of tarantula muscle thick filaments
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Authors
Brito, ReicyAlamo, Lorenzo
Lundberg, Ulf
Guerrero, Jose R.
Pinto, Antonio
Sulbaran, Guidenn
Gawinowicz, Mary Ann
Craig, Roger W.
Padrón, Raúl
UMass Chan Affiliations
Department of Cell BiologyDocument Type
Journal ArticlePublication Date
2011-11-18Keywords
ActinsAnimals
Calcium
Cell Migration Assays
Microscopy, Electron
Models, Molecular
Muscles
Myosin-Light-Chain Kinase
Myosins
Phosphorylation
Serine
Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Spiders
Cell Biology
Metadata
Show full item recordAbstract
Myosin filaments from many muscles are activated by phosphorylation of their regulatory light chains (RLCs). To elucidate the structural mechanism of activation, we have studied RLC phosphorylation in tarantula thick filaments, whose high-resolution structure is known. In the relaxed state, tarantula RLCs are ~50% non-phosphorylated and 50% mono-phosphorylated, while on activation, mono-phosphorylation increases, and some RLCs become bi-phosphorylated. Mass spectrometry shows that relaxed-state mono-phosphorylation occurs on Ser35, while Ca(2+)-activated phosphorylation is on Ser45, both located near the RLC N-terminus. The sequences around these serines suggest that they are the targets for protein kinase C and myosin light chain kinase (MLCK), respectively. The atomic model of the tarantula filament shows that the two myosin heads ("free" and "blocked") are in different environments, with only the free head serines readily accessible to kinases. Thus, protein kinase C Ser35 mono-phosphorylation in relaxed filaments would occur only on the free heads. Structural considerations suggest that these heads are less strongly bound to the filament backbone and may oscillate occasionally between attached and detached states ("swaying" heads). These heads would be available for immediate actin interaction upon Ca(2)(+) activation of the thin filaments. Once MLCK becomes activated, it phosphorylates free heads on Ser45. These heads become fully mobile, exposing blocked head Ser45 to MLCK. This would release the blocked heads, allowing their interaction with actin. On this model, twitch force would be produced by rapid interaction of swaying free heads with activated thin filaments, while prolonged exposure to Ca(2+) on tetanus would recruit new MLCK-activated heads, resulting in force potentiation.Source
J Mol Biol. 2011 Nov 18;414(1):44-61. Epub 2011 Sep 17. Link to article on publisher's siteDOI
10.1016/j.jmb.2011.09.017Permanent Link to this Item
http://hdl.handle.net/20.500.14038/27669PubMed ID
21959262Related Resources
Link to Article in PubMedae974a485f413a2113503eed53cd6c53
10.1016/j.jmb.2011.09.017