Multifaceted effects of ATP on cardiolipin-bound cytochrome c

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Cytochrome c (cyt c) plays a critical role in cellular respiration and apoptosis.
• Cardiolipin (CL) is a unique phospholipid essential for mitochondrial function and interacts with cyt c.
• The functional and structural changes of CL-bound cyt c are not fully understood, especially in the presence of ATP.

Purpose of the Study:

• To investigate the structural transformations of cardiolipin-bound cytochrome c (CL-cyt c) upon addition of adenosine triphosphate (ATP).
• To elucidate the impact of ATP on the peroxidase activity and binding interactions of CL-cyt c.

Main Methods:

• Utilized dye-labeled cytochrome c (cyt c) variants.
• Employed time-resolved fluorescence resonance energy transfer (TR-FRET) to measure dye-to-heme distances (P(r)).
• Assessed peroxidase activity of CL-bound cyt c with and without ATP.

Main Results:

• ATP addition decreased the population of unfolded cyt c conformers in the CL-bound ensemble.
• ATP's effects on cyt c structure differed from those of simple salt solutions.
• CL-bound cyt c exhibited high peroxidase activity in the presence of ATP, indicating a more open heme pocket.
• ATP weakened cyt c-CL binding interactions while simultaneously boosting peroxidase activity.

Conclusions:

• ATP induces distinct structural changes in CL-bound cyt c, favoring conformations with accessible heme pockets.
• Despite weakening binding, ATP enhances the pro-apoptotic peroxidase function of CL-bound cyt c.
• These findings provide insights into the regulation of cyt c activity by ATP in the context of mitochondrial membranes.