pH-dependent structural transition in rabbit skeletal troponin C.

Area of Science:

• Biochemistry
• Structural Biology
• Muscle Contraction

Background:

• The crystal structure of troponin C is known, but its solution structure under physiological conditions remains unclear.
• Understanding troponin C's conformation is crucial for elucidating muscle contraction mechanisms.

Purpose of the Study:

• To investigate the solution conformation of troponin C under varying pH and binding conditions.
• To determine the distance between the N- and C-terminal domains of troponin C in solution.

Main Methods:

• Utilized resonance energy transfer (RET) to measure distances within troponin C.
• Employed terbium (Tb3+) as a luminescent donor and a maleimide derivative as an acceptor.
• Studied troponin C in its uncomplexed form and when complexed with troponin I.

Main Results:

• Uncomplexed troponin C showed a distance greater than 5.2 nm at pH 5.0 and 2.7 nm at pH 6.8.
• Troponin C complexed with troponin I exhibited an intermediate distance of 4.1 nm at pH 6.8.
• These results indicate a pH-dependent conformational change in uncomplexed troponin C.

Conclusions:

• Uncomplexed troponin C transitions from an elongated to a compact conformation as pH increases.
• Complexation with troponin I results in an intermediate conformation, suggesting modulation of troponin C's structural dynamics.
• These findings provide insights into the structural basis of muscle regulation by troponin C.