科研之友
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摘要
The binding of tropomyosin to actin and troponin-tropomyosin to actin was analyzed according to a linear lattice model which quantifies two parameters: K(o), the affinity of the ligand for an isolated site on the actin filament, and y, the fold increase in affinity when binding is contiguous to an occupied site (cooperativity). Tropomyosin-actin binding is very cooperative (y = 90-137). Troponin strengthens tropomyosin-actin binding greatly but, surprisingly, does so solely by an 80-130-fold increase in K(o), while cooperativity actually decreases. Additionally, troponin complexes containing TnT subunits with deletions of either amino acids 1-69 (troponin70-259) or 1-158 (troponin159-259) were examined. Deletion of amino acids 1-69 had only small effects on K(o) and y, despite this peptide's location spanning the joint between adjacent tropomyosins. Ca2+ reduced K(o) by half for both troponin and troponin70-159 and had no detectable effect on cooperativity. Troponin159-259 had much weaker effects on tropomyosin-actin binding than did troponin70-259 and had no effect at all in the presence of Ca2+. This suggests the importance of Ca2+-insensitive interactions between tropomyosin and troponin T residues 70-159. Cooperativity was slightly lower for troponin159-259 than tropomyosin alone, suggesting that the globular head region of troponin affects tropomyosin-tropomyosin interactions along the thin filament.
- 出版日期1992-8-15
