Detection of conserved structural elements in ferredoxins and cupredoxins by resonance Raman spectroscopy

✍ Scribed by Thomas M. Loehr

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 696 KB
• Volume: 23
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/jrs.1250231005

✦ Synopsis

Abstract

Iron‐sulfur proteins and cupredoxins are electron‐transfer proteins containing metal—cysteinate ligation. Both classes of proteins have intense (Cys)S → M~ox~ charge‐transfer bands that are effective for resonance enhancement of Raman‐active modes of vibration of the metal ion chromophores. Resonance Raman (RR) spectroscopy provides a sensitive and powerful method for the investigation of the structural details of the metal clusters. The abundance of normal modes in plant ferredoxins and high‐potential iron proteins has been shown to arise from coupling of the FeS stretching modes with an SCC deformation mode that is at a maximum when the FeSCC dihedral angle is ∼ 180°. X‐ray crystallographic results support these findings. For cupredoxins, the complexity of the RR spectra has been considerably more difficult to understand. However, the availability of several high‐resolution crystal structures of plant and bacterial cupredoxins has shown that the conformation of the cysteinate ligand is highly conserved, and that the five‐atom chain consisting of CuS~γ~C~β~C~α~N is coplanar. This coplanarity provides a mechanism for coupling ν(CuS) with δ(CuSC), δ(SCC) and δ(CCN) deformation modes. Experiments with Cu, N and H isotopes have extended these assignments by revealing the extent of the coupled modes of vibrations. Modern molecular biology techniques are now providing site‐specific ligand mutations that are revolutionizing the study of the metal clusters in these electron‐transfer proteins.