A physical characterization of sulfane sulfurtransferase

Area of Science:

• Biochemistry
• Enzymology
• Protein Structure

Background:

• Sulfane sulfurtransferase is a bacterial enzyme catalyzing sulfur transfer.
• Rhodanese, a well-studied sulfurtransferase, shares similar kinetics and catalytic mechanisms.
• Understanding sulfane sulfurtransferase's structure can elucidate conserved sulfur transfer mechanisms.

Purpose of the Study:

• To characterize the structure of bacterial sulfane sulfurtransferase using spectroscopic techniques.
• To compare the structural properties of sulfane sulfurtransferase with bovine liver rhodanese.
• To gain insights into the intrinsic mechanisms of sulfur atom transfer.

Main Methods:

• Near-UV absorption spectroscopy
• Intrinsic fluorescence spectroscopy with quenching studies
• Second derivative absorption spectroscopy
• Circular dichroism (CD) spectroscopy
• Denaturation-renaturation studies

Main Results:

• Sulfane sulfurtransferase possesses a single, partially solvent-exposed tryptophan residue.
• Most tyrosine residues in sulfane sulfurtransferase are exposed to solvent.
• The enzyme exhibits a higher alpha-helix content compared to rhodanese.
• Unlike rhodanese, sulfane sulfurtransferase shows no detectable quantum yield increase during catalysis.
• Rapid and complete renaturation occurs if the denatured enzyme is not oxidized.

Conclusions:

• Bacterial sulfane sulfurtransferase has distinct structural features, including higher alpha-helix content and different tryptophan exposure, compared to rhodanese.
• The enzyme's structural characteristics do not fully explain the quantum yield changes observed in rhodanese during catalysis.
• Structural insights into sulfane sulfurtransferase contribute to understanding conserved sulfur transfer processes.