The Role of Calcium Ions in the Conformational Changes of Troponin
This paper aims to propose a new 3-dimensional model of troponin C, which can explain as many experimental observations on thin filaments in vertebrate striated muscles as possible. Thin filaments are composed of F-actin, tropomyosin (TM) and troponin. TM is believed to be a double-stranded coiled-coil.1 Troponin consists of 3 components; Ca binding troponin C (TnC), actin-myosin interaction inhibiting troponin I (TnI), and TM binding troponin T (TnT).2 The N-terminal fragment of TnT, viz. T1, is mostly covered by troponins C and I, while the C-terminal fragment of TnT, viz. T2, is more exposed and situated at the N-terminal side of TM.3’4 Troponins C and I are both exposed, but it was not determined by immunoelectron microscopy on which side is actually TnC. The length of TnT is estimated to be longer than 90Å.
KeywordsThin Filament High Affinity Site Actomyosin ATPase Turn Region Actomyosin ATPase Activity
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