Structure and mechanism in the bacterial dihaem cytochrome c peroxidases

Area of Science:

• Biochemistry
• Enzymology
• Protein Science

Background:

• Bacterial cytochrome c peroxidases feature two heme groups: an electron-transferring heme c (E) and a peroxidatic heme c (P).
• These enzymes are often isolated in an inactive, oxidized state, requiring activation for function.
• Ca(2+)-dependent changes in the P heme's spin state and coordination are linked to the reduction of the E heme.

Purpose of the Study:

• To elucidate the mechanism by which electron transfer to the E heme activates the P heme.
• To understand the catalytic cycle of bacterial cytochrome c peroxidases, including peroxide binding and reduction.
• To investigate the interactions between peroxidases and small redox proteins.

Main Methods:

• Utilized crystallographic data of oxidized and mixed-valence enzymes.
• Proposed a mechanism for remote activation of the P heme triggered by electron entry into the E heme.
• Analyzed the binding and electron transfer interactions with small redox proteins like cytochromes and cupredoxins.

Main Results:

• A mechanism suggests electron transfer to the E heme remotely triggers P heme activation.
• Hydrogen peroxide binding to the activated P heme forms a catalytic intermediate with a ferryl oxene.
• The enzyme is reduced by small redox proteins via two single electron transfers to the E heme.
• Redox protein binding is governed by electrostatic forces, with largely hydrophobic and non-specific interfaces.

Conclusions:

• The described mechanism explains the activation of the peroxidatic heme by electron transfer.
• The enzyme efficiently utilizes small redox proteins for catalysis due to favorable binding and electron transfer interfaces.
• These findings provide insights into the functional regulation and high catalytic rates of bacterial cytochrome c peroxidases.