Crystallographic analysis of monomeric CstII

Experimental Data Snapshot

  • Resolution: 2.25 Å
  • R-Value Free: 0.219 
  • R-Value Work: 0.177 
  • R-Value Observed: 0.179 

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NMR Spectroscopic Characterization of the Sialyltransferase Cstii from Camplyobacter Jejuni: Histidine 188 is the General Base.

Chan, P.H.W.Lairson, L.L.Lee, H.J.Wakarchuk, W.W.Strynadka, N.C.J.Withers, S.G.Mcintosh, L.P.

(2009) Biochemistry 48: 11220

  • DOI: https://doi.org/10.1021/bi901606n
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Cell surface glycans are often terminated by sialic acid, which is incorporated onto sugar acceptors by sialyltransferases. The crystal structure of the GT family 42 Campylobacter jejuni alpha-2,3/2,8-sialyltransferase (CstII) provides key insights into the sialyl-transfer mechanism, including tentative identification of His188 as the catalytic base. In support of this hypothesis, the CstII-H188A mutant is able to catalyze sialyl transfer from CMP-Neu5Ac to added anions such as azide and formate but not to its natural sugar acceptor lactose. Complementing this work, NMR spectroscopy was used to investigate the structure and dynamics of CstII and to measure the intrinsic pK(a) value of His188 for comparison with the pK(a) determined from the pH-dependent k(cat)/K(M) of the enzyme. By systematically introducing point mutations at the subunit interfaces, two active monomeric variants, CstII-F121D and CstII-Y125Q, were obtained and characterized. In contrast to the wild-type tetramer, the monomeric CstII variants yielded good quality (1)H/(15)N-HSQC and (1)H/(13)C-methyl-TROSY NMR spectra. However, the absence of signals from approximately one-half of the amides in the (1)H/(15)N-HSQC spectra of both monomeric forms suggests that the enzyme undergoes substantial conformational exchange on a millisecond to microsecond time scale. The histidine pK(a) values of CstII-F121D in its apo form were measured by monitoring the pH-dependent chemical shifts of [(13)C(epsilon1)]histidine, biosynthetically incorporated into the otherwise uniformly deuterated protein. Consistent with its proposed catalytic role, the site-specific pK(a) value approximately 6.6 of His188 matches the apparent pK(a) value approximately 6.5 governing the pH dependence of k(cat)/K(M) for CstII toward CMP-Neu5Ac in the presence of saturating acceptor substrate.

  • Organizational Affiliation

    Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, V6T 1Z3 Canada.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
ALPHA-2,3-/2,8-SIALYLTRANSFERASE291Campylobacter jejuniMutation(s): 3 
EC: 2.4.99
Find proteins for Q9LAK3 (Campylobacter jejuni)
Explore Q9LAK3 
Go to UniProtKB:  Q9LAK3
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ9LAK3
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on CSF

Download Ideal Coordinates CCD File 
C20 H30 F N4 O16 P
Query on PEG

Download Ideal Coordinates CCD File 
C4 H10 O3
Experimental Data & Validation

Experimental Data

  • Resolution: 2.25 Å
  • R-Value Free: 0.219 
  • R-Value Work: 0.177 
  • R-Value Observed: 0.179 
  • Space Group: I 4
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 116.634α = 90
b = 116.634β = 90
c = 45.385γ = 90
Software Package:
Software NamePurpose
MOSFLMdata reduction
SCALAdata scaling

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2009-10-27
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Advisory, Version format compliance
  • Version 1.2: 2011-11-02
    Changes: Database references
  • Version 1.3: 2015-04-01
    Changes: Database references
  • Version 1.4: 2023-12-20
    Changes: Data collection, Database references, Derived calculations, Other, Refinement description