2c9x

From Proteopedia

Revision as of 17:05, 18 December 2007

SULFITE DEHYDROGENASE FROM STARKEYA NOVELLA Y236F MUTANT

Overview

The sulfite dehydrogenase from Starkeya novella is the only known, sulfite-oxidizing enzyme that forms a permanent heterodimeric complex, between a molybdenum and a heme c-containing subunit and can be, crystallized in an electron transfer competent conformation. Tyr236 is a, highly conserved active site residue in sulfite oxidoreductases and has, been shown to interact with a nearby arginine and a molybdenum-oxo ligand, that is involved in catalysis. We have created a Tyr236 to Phe, substitution in the SorAB sulfite dehydrogenase. The purified SDH(Y236F), protein has been characterized in terms of activity, structure, intramolecular electron transfer, and EPR properties. The substituted, protein exhibited reduced turnover rates and substrate affinity as well as, an altered reactivity toward molecular oxygen as an electron acceptor., Following reduction by sulfite and unlike SDH(WT), the substituted enzyme, was reoxidized quickly in the presence of molecular oxygen, a process, reminiscent of the reactions of the sulfite oxidases. SDH(Y236F) also, exhibited the pH-dependent CW-EPR signals that are typically observed in, vertebrate sulfite oxidases, allowing a direct link of CW-EPR properties, to changes caused by a single-amino acid substitution. No quantifiable, electron transfer was seen in laser flash photolysis experiments with, SDH(Y236F). The crystal structure of SDH(Y236F) clearly shows that as a, result of the substitution the hydrogen bonding network surrounding the, active site is disturbed, resulting in an increased mobility of the nearby, arginine. These disruptions underline the importance of Tyr236 for the, integrity of the substrate binding site and the optimal alignment of, Arg55, which appears to be necessary for efficient electron transfer.

About this Structure

2C9X is a Protein complex structure of sequences from Starkeya novella with SO4, MSS and HEC as ligands. Known structural/functional Site: . Full crystallographic information is available from OCA.

Reference

Kinetic and structural evidence for the importance of Tyr236 for the integrity of the Mo active site in a bacterial sulfite dehydrogenase., Kappler U, Bailey S, Feng C, Honeychurch MJ, Hanson GR, Bernhardt PV, Tollin G, Enemark JH, Biochemistry. 2006 Aug 15;45(32):9696-705. PMID:16893171

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