Hexokinase (type II)

 

Yeast Hexokinase PII is one of the two isoenzymes present in Saccharomyces cerevisiae which are able to catalyse the phosphorylation of glucose to glucose-6-phosphate. This is the first step in glycolysis, so is of vital importance as it creates an intermediate which can be passed into many other pathways such as glycogen synthesis and the pentose phosphate pathway. 80% sequence identity is observed between the isoenzymes, and both show significant structural identity to the mammalian form of the enzyme, allowing them to be placed together in the same homologous family.

 

Reference Protein and Structure

Sequence
P04807 UniProt (2.7.1.1) IPR001312 (Sequence Homologues) (PDB Homologues)
Biological species
Saccharomyces cerevisiae S288c (Baker's yeast) Uniprot
PDB
1ig8 - Crystal Structure of Yeast Hexokinase PII with the correct amino acid sequence (2.2 Å) PDBe PDBsum 1ig8
Catalytic CATH Domains
3.30.420.40 CATHdb 3.40.367.20 CATHdb (see all for 1ig8)
Click To Show Structure

Enzyme Reaction (EC:2.7.1.1)

ATP(4-)
CHEBI:30616ChEBI
+
hydroxy group
CHEBI:43176ChEBI
→
ADP(3-)
CHEBI:456216ChEBI
+
phosphate group(2-)
CHEBI:68546ChEBI
+
hydron
CHEBI:15378ChEBI
Alternative enzyme names: ATP-dependent hexokinase, Glucose ATP phosphotransferase, Hexokinase (phosphorylating), Hexokinase D, Hexokinase type IV, Hexokinase type IV glucokinase, Hexokinase type I, Hexokinase type II, Hexokinase type III, Hexokinase type IV (glucokinase),

Enzyme Mechanism

Introduction

The reaction proceeds via an SN2 mechanism with the 6C OH of the glucose acting as a nucleophile, due to deprotonation by Asp 211, to attack the gamma phosphate of ATP. In doing so the position of glucose in the binding site changes to bring it within optimum hydrogen bonding distance of Ser 158, thus stabilising the reaction's transition state. The pentavalent phosphate is stabilised by electrostatic interactions with Lys 173's positively charged side chain.

Catalytic Residues Roles

UniProt PDB* (1ig8)
Ser158 Ser158A Stabilises transition state by binding to the 3OH of glucose when it is making a nucleophilic attack on the gamma phosphate electrostatic stabiliser
Arg173 Arg173A Contacts the gamma phosphate of ATP thus is able to stabilise the pentavalent phosphate transition state through electrostatic interactions. electrostatic stabiliser
Asp211 Asp211A Deprotonates glucose's 6OH group to allow it to act as a nucleophile and attack the gamma phosphate of ATP leading to an SN2 reaction. proton shuttle (general acid/base)
*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. Kuser PR et al. (2000), J Biol Chem, 275, 20814-20821. The High Resolution Crystal Structure of Yeast Hexokinase PII with the Correct Primary Sequence Provides New Insights into Its Mechanism of Action. DOI:10.1074/jbc.m910412199. PMID:10749890.
  2. Arora KK et al. (1991), J Biol Chem, 266, 5359-5362. Glucose phosphorylation. Site-directed mutations which impair the catalytic function of hexokinase. PMID:2005085.

Step 1.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Asp211A proton shuttle (general acid/base)
Ser158A electrostatic stabiliser
Arg173A electrostatic stabiliser

Chemical Components

Step 1.

Contributors

Peter Sarkies, Gemma L. Holliday