Baryshnikova Olga K, Li Monica X, Sykes Brian D
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
J Mol Biol. 2008 Jan 18;375(3):735-51. doi: 10.1016/j.jmb.2007.10.062. Epub 2007 Nov 1.
The cardiac-specific N-terminus of cardiac troponin I (cTnI) is known to modulate the activity of troponin upon phosphorylation with protein kinase A (PKA) by decreasing its Ca(2+) affinity and increasing the relaxation rate of the thin filament. The molecular details of this modulation have not been elaborated to date. We have established that the N-terminus and the switch region of cTnI bind to cNTnC [the N-domain of cardiac troponin C (cTnC)] simultaneously and that the PKA signal is transferred via the cTnI N-terminus modulating the cNTnC affinity toward cTnI(147-163) but not toward Ca(2+). The K(d) of cNTnC for cTnI(147-163) was found to be 600 microM in the presence of cTnI(1-29) and 370 microM in the presence of cTn1(1-29)PP, which can explain the difference in muscle relaxation rates upon the phosphorylation with PKA in experiments with cardiac fibers. In the light of newly found mutations in cNTnC that are associated with cardiomyopathies, the important role played by the cTnI N-terminus in the development of heart disorders emerges. The mutants studied, L29Q (the N-domain of cTnC containing mutation L29Q) and E59D/D75Y (the N-domain of cTnC containing mutation E59D/D75Y), demonstrated unchanged Ca(2+) affinity per se and in complex with the cTnI N-terminus (cTnI(1-29) and cTnI(1-29)PP). The affinity of L29Q and E59D/D75Y toward cTnI(147-163) was significantly perturbed, both alone and in complex with cTnI(1-29) and cTnI(1-29)PP, which is likely to be responsible for the development of malfunctions.
已知心肌肌钙蛋白I（cTnI）的心脏特异性N端在被蛋白激酶A（PKA）磷酸化后，通过降低其对Ca²⁺的亲和力并提高细肌丝的松弛速率来调节肌钙蛋白的活性。迄今为止，这种调节的分子细节尚未阐明。我们已经确定，cTnI的N端和开关区域同时与cNTnC [心肌肌钙蛋白C（cTnC）的N结构域]结合，并且PKA信号通过cTnI N端传递，调节cNTnC对cTnI（147 - 163）的亲和力，但不调节对Ca²⁺的亲和力。发现在存在cTnI（1 - 29）时，cNTnC对cTnI（147 - 163）的解离常数（Kd）为600微摩尔，在存在cTn1（1 - 29）PP时为370微摩尔，这可以解释在心脏纤维实验中PKA磷酸化后肌肉松弛速率的差异。鉴于新发现的与心肌病相关的cNTnC突变，cTnI N端在心脏疾病发展中所起的重要作用显现出来。所研究的突变体，L29Q（包含L29Q突变的cTnC的N结构域）和E59D / D75Y（包含E59D / D75Y突变的cTnC的N结构域），本身以及与cTnI N端（cTnI（1 - 29）和cTnI（1 - 29）PP）形成复合物时，Ca²⁺亲和力均未改变。L29Q和E59D / D75Y对cTnI（147 - 163）的亲和力，无论是单独存在还是与cTnI（1 - 29）和cTnI（1 - 29）PP形成复合物时，都受到显著干扰，这可能是功能障碍发展的原因。
