Faster interprotein electron transfer in a [myoglobin, b⁵] complex with a redesigned interface

Area of Science:

• Biochemistry
• Protein-protein interactions
• Electron transfer dynamics

Background:

• Physiological protein partners myoglobin (Mb) and cytochrome b(5) (b(5)) are crucial for biological electron transfer.
• Understanding interprotein electron transfer (ET) is key to fields like photosynthesis and cellular respiration.
• Redesigning protein interfaces can modulate ET kinetics.

Purpose of the Study:

• To directly measure electron transfer rates in a redesigned myoglobin-cytochrome b(5) complex.
• To investigate the structural basis of interprotein electron transfer using Brownian dynamics simulations.
• To compare measured ET rates with those in natural systems like the photosynthetic reaction center.

Main Methods:

• Engineered a protein-protein complex by mutating surface residues of myoglobin.
• Employed direct measurements to quantify interprotein electron transfer rates.
• Utilized Brownian dynamics simulations to model protein binding configurations and ET pathways.

Main Results:

• Achieved interprotein ET rates comparable to those in the photosynthetic reaction center.
• Identified an ensemble of binding configurations for the myoglobin-cytochrome b(5) complex.
• Observed distributed kinetics for charge-separation and charge-recombination ET.
• Median rate constants for forward (k(f)(s)) and backward (k(b)(s)) ET were 2.1 × 10^9 s⁻¹ and 4.3 × 10^10 s⁻¹, respectively.

Conclusions:

• Engineered protein interfaces can facilitate highly efficient interprotein electron transfer.
• The observed ET rates approach those of the initial charge separation in photosynthesis.
• Structural flexibility and distributed configurations play a significant role in ET kinetics.