Role of Aromatic Residues in Stabilization of the [Fe_4S_4] Cluster in High-Potential Iron Proteins (HiPIPs): Physical Characterization and Stability Studies of Tyr-19 Mutants of Chromatium vinosum HiPIP
Abstract
The functional role of residue Tyr-19 of Chromatium vinosum HiPIP has been evaluated by site-directed mutagenesis experiments. The stability of the [Fe4S4] cluster prosthetic center is sensitive to side-chain replacements. Polar residues result in significant instability, while nonpolar residues (especially with aromatic side chains) maintain cluster stability. Two-dimensional NMR data of native and mutant HiPIPs are consistent with a model where Tyr-19 serves to preserve the structural rigidity of the polypeptide backbone, thereby maintaining a hydrophobic barrier for exclusion of water from the cluster cavity. Solvent accessibility results in more facile oxidation of the cluster by atmospheric oxygen, with subsequent rapid hydrolysis of the [Fe4S4]3+ core.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- October 1995
- DOI:
- 10.1073/pnas.92.21.9440
- Bibcode:
- 1995PNAS...92.9440A