1CIA

REPLACEMENT OF CATALYTIC HISTIDINE-195 OF CHLORAMPHENICOL ACETYLTRANSFERASE: EVIDENCE FOR A GENERAL BASE ROLE FOR GLUTAMATE


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.50 Å
  • R-Value Observed: 0.131 

wwPDB Validation   3D Report Full Report


This is version 1.3 of the entry. See complete history


Literature

Replacement of catalytic histidine-195 of chloramphenicol acetyltransferase: evidence for a general base role for glutamate.

Lewendon, A.Murray, I.A.Shaw, W.V.Gibbs, M.R.Leslie, A.G.

(1994) Biochemistry 33: 1944-1950

  • DOI: https://doi.org/10.1021/bi00173a043
  • Primary Citation of Related Structures:  
    1CIA

  • PubMed Abstract: 

    The imidazole N epsilon 2 of His-195 plays an essential part in the proposed general base mechanism of chloramphenicol acetyltransferase (CAT), hydrogen bonding to and a abstracting a proton from the primary hydroxyl group of chloramphenicol. Replacement of His-195 by alanine or glutamine results in apparent decreases in kcat of (9 x 10(5)- and (3 x 10(5))-fold, respectively, whereas Km values for both substrates (chloramphenicol and acetyl-CoA) are similar to those of wild-type CAT. The structure of Gln-195 CAT has been solved at 2.5-A resolution and is largely isosteric with that of wild-type CAT. Substitution of His-195 by glutamate resulted in a (5 x 10(4))-fold decrease in kcat together with a 3-fold increase in the Km for chloramphenicol. Direct determination of binding constants for both substrates demonstrated that these substitutions result in only small decreases in the affinity of CAT for acetyl-CoA (Kd values increased 2- to 3-fold), whereas chloramphenicol Kd values are elevated 26-, 20-, and 53-fold for Ala-195 CAT, Gln-195 CAT and Glu-195 CAT, respectively. The pH dependence of kcat/Km yields apparent pKa values of 6.5 and 6.7 for Ala-195 CAT and Gln-195 CAT, respectively, which are very similar to that (6.6) determined for the ionization of His-195 in wild-type CAT. In contrast, the pH dependence of kcat/Km for Glu-195 CAT (pKa = 8.3) is very different from that of wild-type CAT.(ABSTRACT TRUNCATED AT 250 WORDS)


  • Organizational Affiliation

    Department of Biochemistry, University of Leicester, U.K.


Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
CHLORAMPHENICOL ACETYLTRANSFERASE213Escherichia coliMutation(s): 0 
EC: 2.3.1.28
UniProt
Find proteins for P00484 (Escherichia coli)
Explore P00484 
Go to UniProtKB:  P00484
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP00484
Sequence Annotations
Expand
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.50 Å
  • R-Value Observed: 0.131 
  • Space Group: H 3 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 107.64α = 90
b = 107.64β = 90
c = 124.13γ = 120
Software Package:
Software NamePurpose
PROLSQrefinement

Structure Validation

View Full Validation Report



Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1994-01-31
    Type: Initial release
  • Version 1.1: 2008-03-24
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Derived calculations, Version format compliance
  • Version 1.3: 2024-02-07
    Changes: Data collection, Database references, Derived calculations, Other