Schaertl S, Lehrer S S, Geeves M A
Max Planck Institute für Molekulare Physiologie, Dortmund, Germany.
Biochemistry. 1995 Dec 12;34(49):15890-4. doi: 10.1021/bi00049a003.
Mild proteolytic cleavage of the troponin complex yields TnT1, the N-terminal fragment of troponin T, and TnT2IC, a complex of the C-terminal fragment of troponin T (TnT2) with troponin I (TnI) and troponin C (TnC) [Morris, E. P., & Lehrer, S. S. (1984) Biochemistry 23, 2214-2220]. Both TnT1 and TnT2IC bind tightly to the tropomyosin.actin (Tm.actin) thin filament and influence the interaction of myosin subfragment 1 (S1) with Tm.actin. TnT1 does not affect the rate of S1 binding to Tm.actin but does increase the cooperativity with which S1 "turns on" Tm.actin, monitored by the excimer fluorescence of a pyrene label attached to Cys 190 of Tm [Geeves, M.A., & Lehrer, S. S. (1994) Biophys. J. 67, 273-282]. The apparent cooperative unit size of Tm.actin is increased from 6 to 9 by TnT1 and to 12 by whole troponin. In contrast, TnT2IC has no effect on the cooperativity of Tm.actin but does make the apparent S1-binding rate constant, kapp, Ca(2+)-sensitive; i.e., in the absence of Ca2+, kapp is reduced 2-3-fold by both TnT2IC and whole troponin. Thus, the N- and C-terminal regions of TnT appear to act independently in modulating effects of S1 binding to the Tm.actin thin filament that are important in regulation.
肌钙蛋白复合物的轻度蛋白水解裂解产生TnT1（肌钙蛋白T的N端片段）和TnT2IC（肌钙蛋白T的C端片段（TnT2）与肌钙蛋白I（TnI）和肌钙蛋白C（TnC）的复合物）[莫里斯，E.P.，&莱勒，S.S.（1984年）《生物化学》23，2214 - 2220]。TnT1和TnT2IC都紧密结合于原肌球蛋白 - 肌动蛋白（Tm.actin）细肌丝，并影响肌球蛋白亚片段1（S1）与Tm.actin的相互作用。TnT1不影响S1与Tm.actin结合的速率，但会增加S1“开启”Tm.actin的协同性，这通过连接到Tm的Cys 190上的芘标记的准分子荧光来监测[吉夫斯，M.A.，&莱勒，S.S.（1994年）《生物物理杂志》67，273 - 282]。TnT1使Tm.actin的表观协同单位大小从6增加到9，而完整肌钙蛋白则使其增加到12。相比之下，TnT2IC对Tm.actin的协同性没有影响，但会使表观S1结合速率常数kapp对Ca(2+)敏感；即，在没有Ca2+的情况下，TnT2IC和完整肌钙蛋白都会使kapp降低2 - 3倍。因此，TnT的N端和C端区域在调节S1与Tm.actin细肌丝结合的效应方面似乎独立发挥作用，这些效应在调节中很重要。
