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Entry M0122    1.8.4.11    protein-methionine-S-oxide reductase

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Step 03

The hydroxyl group deprotonates Cys218, which initiates a nucleophilic attack on Cys72 in a substitution reaction, eliminating water.

GIF of Reaction Step M0122.stg03


Comment: Collapse of the intermediate is facilitated by the concomitant proton transfer from either solvent, Cys218 or other active site donor [3]. Here we show Cys218 as the proton donor. The formation of a disulfide bond between Cys72 and Cys218 is supported by the analysis of double mutants by mass spectrometry and by the inability of dithiothreitol to rescue the lower activity of the Cys218 variants [3].



Mechanisms

Bimolecular Nucleophilic Substitution
Proton Transfer

Mechanism Components

Bond Formation
Bond Cleavage
Enzyme-Substrate Bond Cleavage
Intermediate Terminated
Overall Product Formed
Dehydration

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Tyr155 Side Chain spectator Hydrogen Bond Donor
Glu115 Side Chain spectator Hydrogen Bond Acceptor
Tyr103 Side Chain spectator Hydrogen Bond Donor
Cys72 Side Chain reactant Electrophile
Electrofuge
Cys218 Side Chain reactant Nucleophile
Hydrogen Bond Donor
Proton Donor
Cys227 Side Chain spectator Not Active

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved
O-H
S-S
S-H
S-O
None
H
O
S

View similar reactions in MACiE.


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