TY - JOUR
T1 - Binding Properties of the Calcium-Activated F2 Isoform of Lethocerus Troponin C
AU - Martin, Stephen R.
AU - Avella, Giovanna
AU - Adrover, Miguel
AU - de Nicola, Gian Felice
AU - Bullard, Belinda
AU - Pastore, Annalisa
PY - 2010/3/22
Y1 - 2010/3/22
N2 - While in most muscles contraction is triggered by calcium effluxes, insect flight muscles are also activated by mechanical stretch. We are interested in understanding the role that the troponin C protein, usually the calcium sensor, plays in stretch activation. In the flight muscles of Lethocerus, a giant water bug often used as a model system, there are two isoforms of TnC, F1 and F2, present in an approximately 10:1 ratio. F1 TnC is responsible for activating the muscle following a stretch, whereas F2 TnC produces a sustained contraction, the magnitude of which depends on the concentration of Ca2+ in the fiber. We have previously shown that F1 TnC binds only one Ca2+ ion in its C-terminal domain and that interaction with troponin H, the insect ortholog of troponin I, is insensitive to Ca2+. Here, we have studied the effect of Ca2+ and Mg2+ on the affinities of the interaction of F2 TnC with troponin H peptides. We show that the presence of two Ca2+ ions, one in each of the globular domains, increases the affinity for TnH by at least I order of magnitude. The N lobe has a lower affinity for Ca2+, but it is also sensitive to Mg2+. The C lobe is insensitive to Mg2+ as previously demonstrated by mutations of the individual EF-hands. The interaction with TnH seems also to have significant structural differences from that observed for the F1 TnC isoform. We discuss how our findings could account for stretch activation.
AB - While in most muscles contraction is triggered by calcium effluxes, insect flight muscles are also activated by mechanical stretch. We are interested in understanding the role that the troponin C protein, usually the calcium sensor, plays in stretch activation. In the flight muscles of Lethocerus, a giant water bug often used as a model system, there are two isoforms of TnC, F1 and F2, present in an approximately 10:1 ratio. F1 TnC is responsible for activating the muscle following a stretch, whereas F2 TnC produces a sustained contraction, the magnitude of which depends on the concentration of Ca2+ in the fiber. We have previously shown that F1 TnC binds only one Ca2+ ion in its C-terminal domain and that interaction with troponin H, the insect ortholog of troponin I, is insensitive to Ca2+. Here, we have studied the effect of Ca2+ and Mg2+ on the affinities of the interaction of F2 TnC with troponin H peptides. We show that the presence of two Ca2+ ions, one in each of the globular domains, increases the affinity for TnH by at least I order of magnitude. The N lobe has a lower affinity for Ca2+, but it is also sensitive to Mg2+. The C lobe is insensitive to Mg2+ as previously demonstrated by mutations of the individual EF-hands. The interaction with TnH seems also to have significant structural differences from that observed for the F1 TnC isoform. We discuss how our findings could account for stretch activation.
U2 - 10.1021/bi102076s
DO - 10.1021/bi102076s
M3 - Article
SN - 1520-4995
VL - 50
SP - 1839
EP - 1847
JO - Biochemistry
JF - Biochemistry
IS - 11
ER -