1NKH

Crystal structure of Lactose synthase complex with UDP and Manganese


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Free: 0.251 
  • R-Value Work: 0.196 

wwPDB Validation 3D Report Full Report


This is version 1.2 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
  • Primary Citation of Related Structures:  1J8W, 1J8X, 1J92, 1J94, 1NF5, 1NHE, 1NQI

  • 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-LACTALBUMIN
A, C
123Mus musculusGene Names: Lalba
Find proteins for P29752 (Mus musculus)
Go to UniProtKB:  P29752
Entity ID: 2
MoleculeChainsSequence LengthOrganismDetails
BETA-1,4-GALACTOSYLTRANSFERASE
B, D
286Bos taurusGene Names: B4GALT1 (GALT, GGTB2)
EC: 2.4.1.22, 2.4.1.38, 2.4.1.90, 2.4.1.-
Find proteins for P08037 (Bos taurus)
Go to Gene View: B4GALT1
Go to UniProtKB:  P08037
Small Molecules
Ligands 5 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
MN
Query on MN

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B, D
MANGANESE (II) ION
Mn
WAEMQWOKJMHJLA-UHFFFAOYSA-N
 Ligand Interaction
SO4
Query on SO4

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A, D
SULFATE ION
O4 S
QAOWNCQODCNURD-UHFFFAOYSA-L
 Ligand Interaction
CA
Query on CA

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A, C
CALCIUM ION
Ca
BHPQYMZQTOCNFJ-UHFFFAOYSA-N
 Ligand Interaction
PG4
Query on PG4

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A, B, C, D
TETRAETHYLENE GLYCOL
C8 H18 O5
UWHCKJMYHZGTIT-UHFFFAOYSA-N
 Ligand Interaction
UDP
Query on UDP

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B, D
URIDINE-5'-DIPHOSPHATE
C9 H14 N2 O12 P2
XCCTYIAWTASOJW-XVFCMESISA-N
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Free: 0.251 
  • R-Value Work: 0.196 
  • Space Group: P 1 21 1
Unit Cell:
Length (Å)Angle (°)
a = 55.469α = 90.00
b = 99.145β = 104.14
c = 102.261γ = 90.00
Software Package:
Software NamePurpose
CNSrefinement
AMoREphasing
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

View Full Validation Report or Ramachandran Plots



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2003-01-14
    Type: Initial release
  • Version 1.1: 2008-04-29
    Type: Version format compliance
  • Version 1.2: 2011-07-13
    Type: Version format compliance