1NQI

crystal structure of lactose synthase, a 1:1 complex between beta1,4-galactosyltransferase and alpha-lactalbumin in the presence of GlcNAc


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.00 Å
  • R-Value Free: 0.258 
  • R-Value Work: 0.210 
  • R-Value Observed: 0.211 

wwPDB Validation 3D Report Full Report


This is version 1.3 of the entry. See complete history


Literature

Crystal structure of lactose synthase reveals a large conformational change in its catalytic component, the beta-1,4-galactosyltransferase

Ramakrishnan, B.Qasba, P.K.

(2001) J Mol Biol 310: 205-218

  • DOI: 10.1006/jmbi.2001.4757
  • Structures With Same Primary Citation

  • PubMed Abstract: 
  • The lactose synthase (LS) enzyme is a 1:1 complex of a catalytic component, beta1,4-galactosyltransferse (beta4Gal-T1) and a regulatory component, alpha-lactalbumin (LA), a mammary gland-specific protein. LA promotes the binding of glucose (Glc) to b ...

    The lactose synthase (LS) enzyme is a 1:1 complex of a catalytic component, beta1,4-galactosyltransferse (beta4Gal-T1) and a regulatory component, alpha-lactalbumin (LA), a mammary gland-specific protein. LA promotes the binding of glucose (Glc) to beta4Gal-T1, thereby altering its sugar acceptor specificity from N-acetylglucosamine (GlcNAc) to glucose, which enables LS to synthesize lactose, the major carbohydrate component of milk. The crystal structures of LS bound with various substrates were solved at 2 A resolution. These structures reveal that upon substrate binding to beta4Gal-T1, a large conformational change occurs in the region comprising residues 345 to 365. This repositions His347 in such a way that it can participate in the coordination of a metal ion, and creates a sugar and LA-binding site. At the sugar-acceptor binding site, a hydrophobic N-acetyl group-binding pocket is found, formed by residues Arg359, Phe360 and Ile363. In the Glc-bound structure, this hydrophobic pocket is absent. For the binding of Glc to LS, a reorientation of the Arg359 side-chain occurs, which blocks the hydrophobic pocket and maximizes the interactions with the Glc molecule. Thus, the role of LA is to hold Glc by hydrogen bonding with the O-1 hydroxyl group in the acceptor-binding site on beta4Gal-T1, while the N-acetyl group-binding pocket in beta4Gal-T1 adjusts to maximize the interactions with the Glc molecule. This study provides details of a structural basis for the partially ordered kinetic mechanism proposed for lactose synthase.


    Organizational Affiliation

    Structural Glycobiology Section, Intramural Research Support Program-SAIC, Laboratory of Experimental and Computational Biology, CCR, NCI, Frederick, MD 21702, USA.



Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
ALPHA-LACTALBUMINA, C123Mus musculusMutation(s): 0 
Gene Names: Lalba
Find proteins for P29752 (Mus musculus)
Explore P29752 
Go to UniProtKB:  P29752
Protein Feature View
 ( Mouse scroll to zoom / Hold left click to move )
  • Reference Sequence

Find similar proteins by: Sequence  |  Structure

Entity ID: 2
MoleculeChainsSequence LengthOrganismDetails
BETA-1,4-GALACTOSYLTRANSFERASEB, D286Bos taurusMutation(s): 0 
Gene Names: B4GALT1GALTGGTB2
EC: 2.4.1.22 (PDB Primary Data), 2.4.1.90 (PDB Primary Data), 2.4.1.38 (PDB Primary Data), 2.4.1 (UniProt), 2.4.1.275 (UniProt)
Find proteins for P08037 (Bos taurus)
Explore P08037 
Go to UniProtKB:  P08037
Protein Feature View
 ( Mouse scroll to zoom / Hold left click to move )
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
NAG
Query on NAG

Download CCD File 
B, D
2-acetamido-2-deoxy-beta-D-glucopyranose
C8 H15 N O6
OVRNDRQMDRJTHS-FMDGEEDCSA-N
 Ligand Interaction
CA
Query on CA

Download CCD File 
A, C
CALCIUM ION
Ca
BHPQYMZQTOCNFJ-UHFFFAOYSA-N
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.00 Å
  • R-Value Free: 0.258 
  • R-Value Work: 0.210 
  • R-Value Observed: 0.211 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 57.161α = 90
b = 96.379β = 100.98
c = 99.48γ = 90
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling
AMoREphasing
CNSrefinement

Structure Validation

View Full Validation Report



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2003-02-04
    Type: Initial release
  • Version 1.1: 2008-04-29
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Non-polymer description, Version format compliance
  • Version 1.3: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Data collection, Derived calculations, Structure summary