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Figure 3.
Fig. 3. Proposed reaction mechanism for MsrA catalysis.
Protonation of Met(O) (I) leads to the formation of a sulfonium
ion (II). Possibly concomitant with sulfoxide protonation,
Cys-72 attacks the sulfur atom of the sulfonium ion, leading to
the formation of a covalent intermediate (III). Breakdown of the
complex is facilitated by proton transfer and the attack on
Cys-72 by Cys-218 (IV). Return of the active site to a fully
reduced state (I) is facilitated by thiol  disulfide
exchange via Cys-227 (V) and either DTT or a thioredoxin
regeneration system (VI) (see Discussion for details).
Abbreviations: TR, thioredoxin; TRR, thioredoxin reductase.
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