Entry M0277    mercury(II) reductase

Next Step

Step 01

The distal sulfur of Cys11 acts as a nucleophile towards the Hg(II) complex.

GIF of Reaction Step M0277.stg01

Comment: The catalytic centre is activated towards its function in the presence of NADPH. The group reduces a disulfide bond between Cys141 and Cys136, forming the dithiol species which is necessary for catalysis to occur. A charge transfer complex exists between the FAD cofactor and Cys141 [3].
The two N terminal Cys residues (Cys11/Cys14) form part of a soft-metal binding domain. The positive charge of the N terminus, as well as the presence of specific interactions with surrounding residues lowers the pKa of these cysteine thiols relative to unstructured peptide analogues, enhancing their nucleophilic character and therefore their reactivity with Hg over other peptide sequences.


Bimolecular Nucleophilic Substitution

Mechanism Components

Bond Cleavage
Bond Formation
Overall Reactant Used
Enzyme-Substrate Bond Formation
Intermediate Formation

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Cys558B Side Chain spectator Not Active
Met9A Side Chain spectator Steric Role
Electrostatic Stabiliser
Tyr65A Side Chain spectator Electrostatic Stabiliser
Hydrogen Bond Acceptor
Cys559B Side Chain spectator Not Active
Cys14A Side Chain spectator Electrostatic Stabiliser
Increase Nucleophilicity
Cys11A Side Chain reactant Activator
Metal Ligand
Cys141A Side Chain spectator Not Active
Cys136A Side Chain spectator Not Active

Organic Cofactors involved in the reaction step

Cofactor Type Cofactor Activity Function
FAD FAD666A spectator Electrostatic Stabiliser
Increase Acidity

Metal Cofactors involved in Step 01

Metal Type Metal Identity Chain Activity Function
mercury No Information available from the PDB spectator Not Active

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved

View similar reactions in MACiE.