Single-molecule spectroscopy exposes hidden states in an enzymatic electron relay

Area of Science:

• Biochemistry
• Enzymology
• Biophysics

Background:

• Quiescin sulfhydryl oxidase (QSOX) is a key enzyme catalyzing disulfide-bond formation.
• Electron transfer mechanisms in QSOX are known, but associated conformational changes remain poorly understood.
• Understanding these dynamics is crucial for elucidating complex enzymatic catalysis.

Purpose of the Study:

• To investigate the conformational dynamics of QSOX during its catalytic cycle.
• To identify the roles of protein motion in QSOX enzymatic activity.
• To expand the kinetic model of QSOX by incorporating conformational transitions.

Main Methods:

• Utilized single-molecule Förster resonance energy transfer (smFRET) to monitor QSOX conformation.
• Studied enzyme populations in both resting and actively cycling states.
• Applied smFRET data to constrain and refine mechanistic enzymatic models.

Main Results:

• Discovered previously uncharacterized conformational changes in QSOX.
• Identified novel roles for these dynamics beyond electron transfer between redox sites.
• Revealed a new enzyme state, gated by a conformational transition, that controls entry into a sub-cycle.

Conclusions:

• Conformational changes play critical, unanticipated roles in QSOX catalysis.
• smFRET is a powerful tool for linking protein dynamics to chemical transitions.
• The findings expand the mechanistic understanding of QSOX and complex enzyme systems.