Which troponin subunit is responsible for calcium binding?
Troponin heterotrimer every 38 nanometer along thin filament alongside tropomyosin provides calcium dependent switch. Subunits: TnT 30 to 35 kilodalton tropomyosin binding anchoring complex, TnI 21 to 24 kilodalton inhibitory binding actin blocking myosin in diastole, TnC 18 kilodalton calcium binding sensor homologous to calmodulin containing four EF hand helix loop helix motifs. N terminal low affinity regulatory sites I II bind calcium transiently during systole with Kd 5 micromolar triggering activation, affinity modulated by magnesium competition, C terminal high affinity structural sites
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 18: Troponin C as Calcium-Binding Subunit.
