Energetic basis on interactions between ferredoxin and ferredoxin NADP{sup +} reductase at varying physiological conditions
- Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka, 565-0871 (Japan)
- Cellular Function Imaging Team, Division of Bio-function Dynamics Imaging, RIKEN Center for Life Science Technologies, Kobe, Hyogo, 650-0047 (Japan)
- Trinity College Dublin, Trinity Biomedical Sciences Institute (TBSI), School of Biochemistry & Immunology, Dublin 2 (Ireland)
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo (Japan)
- Malvern Instrument Inc., 22 Industrial Drive East, Northampton, MA, 01060 (United States)
In spite of a number of studies to characterize ferredoxin (Fd):ferredoxin NADP{sup +} reductase (FNR) interactions at limited conditions, detailed energetic investigation on how these proteins interact under near physiological conditions and its linkage to FNR activity are still lacking. We herein performed systematic Fd:FNR binding thermodynamics using isothermal titration calorimetry (ITC) at distinct pH (6.0 and 8.0), NaCl concentrations (0–200 mM), and temperatures (19–28 °C) for mimicking physiological conditions in chloroplasts. Energetically unfavorable endothermic enthalpy changes were accompanied by Fd:FNR complexation at all conditions. This energetic cost was compensated by favorable entropy changes, balanced by conformational and hydrational entropy. Increases in the NaCl concentration and pH weakened interprotein affinity due to the less contribution of favorable entropy change regardless of energetic gains from enthalpy changes, suggesting that entropy drove complexation and modulated affinity. Effects of temperature on binding thermodynamics were much smaller than those of pH and NaCl. NaCl concentration and pH-dependent enthalpy and heat capacity changes provided clues for distinct binding modes. Moreover, decreases in the enthalpy level in the Hammond's postulate-based energy landscape implicated kinetic advantages for FNR activity. All these energetic interplays were comprehensively demonstrated by the driving force plot with the enthalpy-entropy compensation which may serve as an energetic buffer against outer stresses. We propose that high affinity at pH 6.0 may be beneficial for protection from proteolysis of Fd and FNR in rest states, and moderate affinity at pH 8.0 and proper NaCl concentrations with smaller endothermic enthalpy changes may contribute to increase FNR activity. - Highlights: • Energetics of Fd:FNR binding were examined by considering physiological conditions. • NaCl and pH affect energetically Fd:FNR binding with minimal effects of temperature. • Enthalpy and heat capacity may modulate binding kinetics and modes for FNR activity. • Entropy drives complexation by overcoming unfavorable enthalpy and tunes affinity. • Driving force plot reveals condition-dependent energetic interplays for complexation.
- OSTI ID:
- 22696786
- Journal Information:
- Biochemical and Biophysical Research Communications, Vol. 482, Issue 4; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0006-291X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Concentration-dependent oligomerization of cross-linked complexes between ferredoxin and ferredoxin–NADP{sup +} reductase
Electrostatic and hydrophobic interactions during complex formation and electron transfer in the ferredoxin/ferredoxin: NADP{sup +} reductase system from Anabaena