Chimeric Substitutions of the Actin-binding Loop Activate Dephosphorylated but Not Phosphorylated Smooth Muscle Heavy Meromyosin
| Autor: | Kathleen M. Trybus, Arthur S. Rovner, Yelena Freyzon |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Turkeys
Sp1 Transcription Factor Recombinant Fusion Proteins Molecular Sequence Data Motility macromolecular substances Myosins Spodoptera Biology Transfection Immunoglobulin light chain Biochemistry Cell Line Myosin Animals Nucleotide Amino Acid Sequence Phosphorylation Muscle Skeletal Molecular Biology Actin chemistry.chemical_classification Binding Sites Meromyosin Heavy meromyosin Myosin Subfragments Muscle Smooth Cell Biology Actins Kinetics chemistry Gizzard Avian Trans-Activators Biophysics Chickens |
| Zdroj: | Journal of Biological Chemistry. 270:30260-30263 |
| ISSN: | 0021-9258 |
| DOI: | 10.1074/jbc.270.51.30260 |
| Popis: | Regulatory light chain (RLC) phosphorylation is necessary to activate smooth muscle myosin, unlike constitutively active striated muscle myosins. Here we show that an actin-binding surface loop located at the 50/20-kDa junction contributes to this fundamental difference between myosins. Substitution of the native actin-binding loop of smooth muscle heavy meromyosin (HMM) with that from either skeletal or β-cardiac myosin caused the chimeric HMMs to become unregulated like the myosin from which the loop was derived. Dephosphorylated chimeric HMMs gained the ability to move actin in a motility assay and had 50-70% of the actin-activated ATPase activity of phosphorylated wild-type HMM. Direct binding measurements showed that the affinity of HMM for actin in the presence of MgATP was unaffected by loop substitution; thus the rate of a step other than binding is increased. Phosphorylation of the chimeras did not lead to a higher Vmax than obtained for wild-type HMM. In the absence of actin, a foreign loop did not affect nucleotide trapping. Native regulated molecules have thus evolved a loop sequence which prevents rapid product release by actin when the RLC is dephosphorylated, thereby allowing activity to be controlled by RLC phosphorylation. |
| Databáze: | OpenAIRE |
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