Download MendeleyThe role of extended Fe4S4cluster ligands in mediating sulfite reductase hemoprotein activity.
Cepeda, M.R., McGarry, L., Pennington, J.M., Krzystek, J., Stroupe, M.E.(2018) Biochim Biophys Acta 1866: 933-940
- PubMed: 29852252
- DOI: https://doi.org/10.1016/j.bbapap.2018.05.013
- Primary Citation of Related Structures:
6C3M, 6C3X, 6C3Y, 6C3Z - PubMed Abstract:
The siroheme-containing subunit from the multimeric hemoflavoprotein NADPH-dependent sulfite reductase (SiR/SiRHP) catalyzes the six electron-reduction of SO 3 2- to S 2- . Siroheme is an iron-containing isobacteriochlorin that is found in sulfite and homologous siroheme-containing nitrite reductases. Siroheme does not work alone but is covalently coupled to a Fe 4 S 4 cluster through one of the cluster's ligands. One long-standing hypothesis predicted from this observation is that the environment of one iron-containing cofactor influences the properties of the other. We tested this hypothesis by identifying three amino acids (F437, M444, and T477) that interact with the Fe 4 S 4 cluster and probing the effect of altering them to alanine on the function and structure of the resulting enzymes by use of activity assays, X-ray crystallographic analysis, and EPR spectroscopy. We showed that F437 and M444 gate access for electron transfer to the siroheme-cluster assembly and the direct hydrogen bond between T477 and one of the cluster sulfides is important for determining the geometry of the siroheme active site.
Organizational Affiliation:
Department of Biological Science, Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA; Department of Biological Sciences, Georgia Institute of Technology, 310 Ferst Dr. NW, Atlanta, CA 30332, USA.
