Crystal structure of the putidaredoxin reductase x putidaredoxin electron transfer complex.

Area of Science:

• Biochemistry
• Structural Biology
• Enzyme Mechanisms

Background:

• The camphor monooxygenase system in Pseudomonas putida utilizes putidaredoxin (Pdx) to transfer electrons from putidaredoxin reductase (Pdr) to cytochrome P450(cam).
• Understanding the Pdr-Pdx interaction is crucial for elucidating the electron transfer mechanism, but native partners exhibit weak association, hindering structural studies.

Purpose of the Study:

• To determine the X-ray crystal structure of a catalytically active complex between Pdr and Pdx.
• To provide insights into the molecular basis of electron transfer between Pdr and Pdx.

Main Methods:

• X-ray crystallography was employed to obtain a 2.6-Å resolution structure.
• A chemically cross-linked Pdr-Pdx complex (C73S/C85S Pdx) was engineered to facilitate co-crystallization.

Main Results:

• The structure reveals a 365 Ų Pdr-Pdx interface characterized by hydrophobic interactions and a key Arg(310Pdr)-Asp(38Pdx) salt bridge.
• A predicted 12-Å electron transfer pathway involves flavin-flanking Trp(330Pdr) and the iron ligand Cys(39Pdx).
• The model suggests Pdx undergoes conformational changes during electron transfer, potentially impacting efficiency.

Conclusions:

• The determined structure provides a detailed view of the Pdr-Pdx complex, supporting existing experimental and theoretical data.
• The findings highlight the dynamic nature of Pdx and its potential role in regulating electron transfer to cytochrome P450(cam).