Arsenite-transporting ATPase

 

The ArsAB pump is able to catalyse the active transport of toxic heavy metal ions out of the cell. Since heavy metal ions such as arsenic are able to bind irreversibly to many enzymes and permanently deactivate them, it is essential for the survival of the organism that such pumps work correctly; inhibition of these pumps in bacteria may therefore be an antibiotic target. The enzyme uses changes in the tertiary structure that occur when ATP is hydrolysed in order to power the transport of the heavy metal ions against the concentration gradient across the cell membrane, and is activated by the binding of metalloids such as antimony (Sb III) to allosteric sites. The transporter is part of a wider family of ATP utilising proteins, all of which display the Rossman fold, including such well known examples as the ABC transporters.

 

Reference Protein and Structure

Sequence
P08690 UniProt (7.3.2.7) IPR027541 (Sequence Homologues) (PDB Homologues)
Biological species
Escherichia coli (Bacteria) Uniprot
PDB
1f48 - CRYSTAL STRUCTURE OF THE ESCHERICHIA COLI ARSENITE-TRANSLOCATING ATPASE (2.3 Å) PDBe PDBsum 1f48
Catalytic CATH Domains
3.40.50.300 CATHdb (see all for 1f48)
Cofactors
Magnesium(2+) (1)
Click To Show Structure

Enzyme Reaction (EC:7.3.2.7)

arsenite(1-)
CHEBI:29242ChEBI
+
water
CHEBI:15377ChEBI
+
ATP(4-)
CHEBI:30616ChEBI
→
hydrogenphosphate
CHEBI:43474ChEBI
+
arsenite(1-)
CHEBI:29242ChEBI
+
ADP(3-)
CHEBI:456216ChEBI
+
hydron
CHEBI:15378ChEBI
Alternative enzyme names: Arsenite-translocating ATPase, Arsenical resistance ATPase, Arsenical pump-driving ATPase,

Enzyme Mechanism

Introduction

The catalytic activity of the ATP hydrolysing subunit of the protein is provided by the residues Lys 21 and Gly 18, along with Mg2+, all of which act together to stabilise the pentavalent phosphate transition state that forms when a water molecule acts as a nucleophile to attack the gamma phosphate of ATP. The phosphate leaving group acts as the base to deprotonate the water molecule.

Catalytic Residues Roles

UniProt PDB* (1f48)
Gly18 (main-N) Gly18A (main-N) Amide forms electrostatic contacts with the gamma phosphate of ATP, thus stabilises the pentavalent phosphate transition state. electrostatic stabiliser
Thr22, Asp45 Thr22A, Asp45A Form magnesium binding site
Ser23, Lys21 (main-N), Gly20 (main-N), Thr502 Ser23A, Lys21A (main-N), Gly20A (main-N), Thr502A Form phosphate binding site and stabilise negative charges on phosphates
Lys21 Lys21A Forms contacts with the gamma phosphate of ATP, thus stabilises the pentavalent phosphate intermediate. electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

References

  1. Zhou T et al. (2000), EMBO J, 19, 4838-4845. Structure of the ArsA ATPase: the catalytic subunit of a heavy metal resistance pump. DOI:10.1093/emboj/19.17.4838. PMID:10970874.
  2. Bhattacharjee H et al. (2008), Biochemistry, 47, 7218-7227. Role of conserved aspartates in the ArsA ATPase. DOI:10.1021/bi800715h. PMID:18553931.

Step 1.

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Catalytic Residues Roles

Residue Roles
Lys21A electrostatic stabiliser
Gly18A (main-N) electrostatic stabiliser

Chemical Components

Step 1.

Contributors

Peter Sarkies, Gemma L. Holliday, Charity Hornby