Protein-Npi-phosphohistidine---sugar phosphotransferase (type III)

 

Enzyme II lactose belongs to a class of lactose/cellubiose-specific family of enzymes II which act as sugar specific permeases. The enzyme is involved in the phosphotransferase system (PTS), a mechanism responsible for the specific binding, transmembrane transport and phosphorylation of a carbohydrate substrate. The PTS is a major carbohydrate transport system in bacteria and catalyses the phosphorylation of incoming sugar substrates, coupled with translocation across the cell membrane. The function of PTS enzymes makes this system a link between the uptake and metabolism of sugars.

The complete PTS acts as follows: a phosphoryl group from phosphoenolpyruvate (PEP) is transferred via a signal transduction pathway, to enzyme I (EI) which in turn transfers it to a phosphoryl carrier, the histidine protein (HPr). Phospho-HPr (the substrate for this entry) then transfers the phosphoryl group to a sugar-specific permease, a membrane-bound complex known as enzyme 2 (EII), which transports the sugar to the cell. EII consists of at least three structurally distinct domains IIA, IIB and IIC [PMID:1537788]. These can either be fused together in a single polypeptide chain or exist as two or three interactive chains, formerly called enzymes II (EII) and III (EIII).

 

Reference Protein and Structure

Sequence
P23532 UniProt IPR003188 (Sequence Homologues) (PDB Homologues)
Biological species
Lactococcus lactis subsp. lactis (Bacteria) Uniprot
PDB
1e2a - ENZYME IIA FROM THE LACTOSE SPECIFIC PTS FROM LACTOCOCCUS LACTIS (2.3 Å) PDBe PDBsum 1e2a
Catalytic CATH Domains
1.20.58.80 CATHdb (see all for 1e2a)
Click To Show Structure

Enzyme Reaction (EC:2.7.1.191)

D-mannopyranose
CHEBI:4208ChEBI
+
N(pros)-phosphonato-L-histidine residue
CHEBI:64837ChEBI
→
D-mannopyranose 6-phosphate(2-)
CHEBI:58735ChEBI
+
L-histidine residue
CHEBI:29979ChEBI
Alternative enzyme names: ManXYZ (gene names), Mannose PTS permease, EII(Man), Enzyme II(Man),

Enzyme Mechanism

Introduction

The transfer of a phosphoryl group from a heat stable phosphocarrier binding protein to Enzyme II occurs at His 78 phosphorylation sites within each chain of the the homotrimer. The eta N of His 78 acts as a nucleophile towards the phosphoryl group on the carrier protein. An electrostatic interaction exists between the residue and the phophoryl group present on the substrate. Hydrogen bonds are present between the delta N of His 78 and a water molecule held in the active site, as well as Asp 81 and Glu 80. These interactions hold the catalytic residue in a distinct conformation.

Catalytic Residues Roles

UniProt PDB* (1e2a)
His78 His78A The residue eta N atom acts as a nucleophile towards the phosphoryl carrier protein substrate, as indicated by pH studies which show the atom to be deprotonated at physiological pH levels. The protonated delta N is involved in a hydrogen bond network which directs the position of the catalytic residue within the active site. covalent catalysis, electrostatic stabiliser
Gln80 Gln80A The residue hydrogen bonds to the Hist 78 delta N, directing the position of the nucleophilic eta N within the active site. The residue is also hydrogen bonded to an embedded water molecule. The hydrogen bond network acts to rigidity the phosphorylation site. electrostatic stabiliser
His82 His82A The residue acts to stabilise the histidine bound phosphate in the phosphorylation 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. Sliz P et al. (1997), Structure, 5, 775-788. The structure of enzyme IIAlactose from Lactococcus lactis reveals a new fold and points to possible interactions of a multicomponent system. DOI:10.1016/s0969-2126(97)00232-3. PMID:9261069.
  2. Jung YS et al. (2012), J Biol Chem, 287, 23819-23829. Solution structure of the IIAChitobiose-HPr complex of the N,N'-diacetylchitobiose branch of the Escherichia coli phosphotransferase system. DOI:10.1074/jbc.M112.371492. PMID:22593574.
  3. Saier MH Jr et al. (1992), J Bacteriol, 174, 1433-1438. Proposed uniform nomenclature for the proteins and protein domains of the bacterial phosphoenolpyruvate: sugar phosphotransferase system. PMID:1537788.

Step 1.

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Catalytic Residues Roles

Residue Roles
His78A electrostatic stabiliser
His82A electrostatic stabiliser
Gln80A electrostatic stabiliser
His78A covalent catalysis

Chemical Components

Step 1.

Contributors

James W. Murray, Craig Porter, Gemma L. Holliday