Premium
Calcium‐regulated conformational change in the C‐terminal end segment of troponin I and its binding to tropomyosin
Author(s) -
Zhang Zhiling,
Akhter Shirin,
Mottl Steven,
Jin JianPing
Publication year - 2011
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2011.08250.x
Subject(s) - terminal (telecommunication) , tropomyosin , calcium , troponin , chemistry , biophysics , conformational change , actin , biochemistry , computer science , medicine , biology , telecommunications , organic chemistry , myocardial infarction
The troponin complex plays an essential role in the thin filament regulation of striated muscle contraction. Of the three subunits of troponin, troponin I (TnI) is the actomyosin ATPase inhibitory subunit and its effect is released upon Ca 2+ binding to troponin C. The exon‐8‐encoded C‐terminal end segment represented by the last 24 amino acids of cardiac TnI is highly conserved and is critical to the inhibitory function of troponin. Here, we investigated the function and calcium regulation of the C‐terminal end segment of TnI. A TnI model molecule was labeled with Alexa Fluor 532 at a Cys engineered at the C‐terminal end and used to reconstitute the tertiary troponin complex. A Ca 2+ ‐regulated conformational change in the C‐terminus of TnI was shown by a sigmoid‐shape fluorescence intensity titration curve similar to that of the CD calcium titration curve of troponin C. Such corresponding Ca 2+ responses are consistent with the function of troponin as a coordinated molecular switch. Reconstituted troponin complex containing a mini‐troponin T lacking its two tropomyosin‐binding sites showed a saturable binding to tropomyosin at pCa 9 but not at pCa 4. This Ca 2+ ‐regulated binding was diminished when the C‐terminal 19 amino acids of cardiac TnI were removed. These results provided novel evidence for suggesting that the C‐terminal end segment of TnI participates in the Ca 2+ regulation of muscle thin filament through interaction with tropomyosin. Structured digital abstract• McTnT binds to Tropomyosin by enzyme linked immunosorbent assay (View interaction)• McTnI binds to TnC by enzyme linked immunosorbent assay (View interaction)• Tropomyosin physically interacts with McTnT and McTnI by enzyme linked immunosorbent assay (View interaction)• McTnI binds to TnT by enzyme linked immunosorbent assay (View interaction)