1SS9

Crystal Structural Analysis of Active Site Mutant Q189E of LgtC


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.60 Å
  • R-Value Free: 0.283 
  • R-Value Work: 0.217 
  • R-Value Observed: 0.217 

wwPDB Validation   3D Report Full Report


This is version 1.2 of the entry. See complete history


Literature

Intermediate trapping on a mutant retaining alpha-galactosyltransferase identifies an unexpected aspartate residue.

Lairson, L.L.Chiu, C.P.Ly, H.D.He, S.Wakarchuk, W.W.Strynadka, N.C.Withers, S.G.

(2004) J Biol Chem 279: 28339-28344

  • DOI: 10.1074/jbc.M400451200
  • Primary Citation of Related Structures:  
    1SS9

  • PubMed Abstract: 
  • Lipopolysaccharyl-alpha-1,4-galactosyltransferase C (LgtC), a glycosyltransferase family 8 alpha-1,4-galactosyltransferase from Neisseria meningitidis, catalyzes the transfer of galactose from UDP galactose to terminal lactose-containing acceptor sugars with net retention of anomeric configuration ...

    Lipopolysaccharyl-alpha-1,4-galactosyltransferase C (LgtC), a glycosyltransferase family 8 alpha-1,4-galactosyltransferase from Neisseria meningitidis, catalyzes the transfer of galactose from UDP galactose to terminal lactose-containing acceptor sugars with net retention of anomeric configuration. To investigate the potential role of discrete nucleophilic catalysis suggested by the double displacement mechanism generally proposed for retaining glycosyltransferases, the side chain amide of Gln-189, which is suitably positioned to act as the catalytic nucleophile of LgtC, was substituted with the more nucleophilic carboxylate-containing side chain of glutamate in the hope of accumulating a glycosyl-enzyme intermediate. The resulting mutant was subjected to kinetic, mass spectrometric, and x-ray crystallographic analysis. Although the K(m) for UDP-galactose is not significantly altered, the k(cat) was reduced to 3% that of the wild type enzyme. Electrospray mass spectrometric analysis revealed that a steady state population of the Q189E variant contains a covalently bound galactosyl moiety. Liquid chromatographic/mass spectrometric analysis of fragmented proteolytic digests identified the site of labeling not as Glu-189 but, surprisingly, as the sequentially adjacent Asp-190. However, the side chain carboxylate of Asp-190 is located 8.9 A away from the donor substrate in the available crystal structure. Kinetic analysis of a D190N mutant at this position revealed a k(cat) value 3000-fold lower than that of the wild type enzyme. A 2.6-A crystal structure of the Q189E mutant with bound uridine 5'-diphospho-2-deoxy-2-fluoro-alpha-d-galactopyranose revealed no significant perturbation of the mode of donor sugar binding nor of active site configuration. This is the first trapping of an intermediate in the active site of a retaining glycosyltransferase and, although not conclusive, implicates Asp-190 as an alternative candidate catalytic nucleophile, thereby rekindling a longstanding mechanistic debate.


    Organizational Affiliation

    Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.



Macromolecules
Find similar proteins by:  (by identity cutoff)  |  Structure
Entity ID: 1
MoleculeChainsSequence LengthOrganismDetailsImage
alpha-1,4-galactosyl transferase A311Neisseria meningitidisMutation(s): 1 
Gene Names: lgtC
EC: 2.4.1.44
Find proteins for Q93EK7 (Neisseria meningitidis)
Explore Q93EK7 
Go to UniProtKB:  Q93EK7
Protein Feature View
Expand
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
UPF
Query on UPF

Download Ideal Coordinates CCD File 
A
URIDINE-5'-DIPHOSPHATE-2-DEOXY-2-FLUOROGALACTOSE
C15 H23 F N2 O16 P2
NGTCPFGWXMBZEP-KBQKSTHMSA-N
 Ligand Interaction
MN
Query on MN

Download Ideal Coordinates CCD File 
A
MANGANESE (II) ION
Mn
WAEMQWOKJMHJLA-UHFFFAOYSA-N
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.60 Å
  • R-Value Free: 0.283 
  • R-Value Work: 0.217 
  • R-Value Observed: 0.217 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 39.85α = 90
b = 75.934β = 90
c = 86.905γ = 90
Software Package:
Software NamePurpose
CNSrefinement
DENZOdata reduction
SCALEPACKdata scaling
AMoREphasing

Structure Validation

View Full Validation Report



Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2004-09-21
    Type: Initial release
  • Version 1.1: 2008-04-29
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance