Elucidation of a [4Fe-4S] cluster degradation pathway: rapid kinetic studies of the degradation of Chromatium vinosum HiPIP.

Published

Journal Article

Irreversible disassembly of the 4Fe-4S cluster in Chromatium vinosum high-potential iron protein (HiPIP) has been investigated in the presence of a low concentration of guanidinium hydrochloride. From the dependence of degradation rate on [H+], it is deduced that at least three protons are required to trigger efficient cluster degradation. Under these conditions the protonated cluster shows broadened Mössbauer signals, but delta EQ (1.1 mm/s) and delta (0.44 mm/s) are similar to the native form. Collapse of the protonated transition state complex, revealed by rapid-quench Mössbauer experiments, occurs with a measured rate constant kobs approximately 0.72 +/- 0.35 s-1 that is consistent with results from time-resolved electronic absorption and fluorescence (kobs approximately 0.4 +/- 0.1 s-1) and EPR (kobs approximately 0.62 +/- 0.18 s-1) measurements. Apparently, guanidinium hydrochloride serves to perturb the tertiary structure of the protein, facilitating protonation of the cluster, but not degradation per se. Release of iron ions occurs even more slowly with kobs approximately 0.07 +/- 0.02 s-1, as determined by the appearance of the g = 4.3 EPR signal. Proton-mediated cluster degradation is sensitive to the oxidation state of the cluster, with the oxidized state showing a two-fold slower rate in acidic solutions as a result of increased electrostatic repulsion with the cluster. Consistent results are obtained from absorption, fluorescence, Mössbauer and EPR measurements.

Full Text

Duke Authors

Cited Authors

  • Foster, MW; Bian, S; Surerus, KK; Cowan, JA

Published Date

  • March 2001

Published In

Volume / Issue

  • 6 / 3

Start / End Page

  • 266 - 274

PubMed ID

  • 11315562

Pubmed Central ID

  • 11315562

International Standard Serial Number (ISSN)

  • 0949-8257

Digital Object Identifier (DOI)

  • 10.1007/s007750000196

Language

  • eng

Conference Location

  • Germany