1XJW

The Structure of E. coli Aspartate Transcarbamoylase Q137A Mutant in The R-State


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.71 Å
  • R-Value Free: 0.223 
  • R-Value Work: 0.170 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

A Single Amino Acid Substitution in the Active Site of Escherichia coli Aspartate Transcarbamoylase Prevents the Allosteric Transition.

Stieglitz, K.A.Pastra-Landis, S.C.Xia, J.Tsuruta, H.Kantrowitz, E.R.

(2005) J.Mol.Biol. 349: 413-423

  • DOI: 10.1016/j.jmb.2005.03.073

  • PubMed Abstract: 
  • Modeling of the tetrahedral intermediate within the active site of Escherichia coli aspartate transcarbamoylase revealed a specific interaction with the side-chain of Gln137, an interaction not previously observed in the structure of the X-ray enzyme ...

    Modeling of the tetrahedral intermediate within the active site of Escherichia coli aspartate transcarbamoylase revealed a specific interaction with the side-chain of Gln137, an interaction not previously observed in the structure of the X-ray enzyme in the presence of N-phosphonacetyl-L-aspartate (PALA). Previous site-specific mutagenesis experiments showed that when Gln137 was replaced by alanine, the resulting mutant enzyme (Q137A) exhibited approximately 50-fold less activity than the wild-type enzyme, exhibited no homotropic cooperativity, and the binding of both carbamoyl phosphate and aspartate were extremely compromised. To elucidate the structural alterations in the mutant enzyme that might lead to such pronounced changes in kinetic and binding properties, the Q137A enzyme was studied by time-resolved, small-angle X-ray scattering and its structure was determined in the presence of PALA to 2.7 angstroms resolution. Time-resolved, small-angle X-ray scattering established that the natural substrates, carbamoyl phosphate and L-aspartate, do not induce in the Q137A enzyme the same conformational changes as observed for the wild-type enzyme, although the scattering pattern of the Q137A and wild-type enzymes in the presence of PALA were identical. The overall structure of the Q137A enzyme is similar to that of the R-state structure of wild-type enzyme with PALA bound. However, there are differences in the manner by which the Q137A enzyme coordinates PALA, especially in the side-chain positions of Arg105 and His134. The replacement of Gln137 by Ala also has a dramatic effect on the electrostatics of the active site. These data taken together suggest that the side-chain of Gln137 in the wild-type enzyme is required for the binding of carbamoyl phosphate in the proper orientation so as to induce conformational changes required for the creation of the high-affinity aspartate-binding site. The inability of carbamoyl phosphate to create the high-affinity binding site in the Q137A enzyme results in an enzyme locked in the low-activity low-affinity T state. These results emphasize the absolute requirement of the binding of carbamoyl phosphate for the creation of the high-affinity aspartate-binding site and for inducing the homotropic cooperativity in aspartate transcarbamoylase.


    Organizational Affiliation

    Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
Aspartate carbamoyltransferase catalytic chain
A, C
310Escherichia coli (strain K12)Mutation(s): 1 
Gene Names: pyrB
EC: 2.1.3.2
Find proteins for P0A786 (Escherichia coli (strain K12))
Go to UniProtKB:  P0A786
Entity ID: 2
MoleculeChainsSequence LengthOrganismDetails
Aspartate carbamoyltransferase regulatory chain
B, D
153Escherichia coli (strain K12)Mutation(s): 0 
Gene Names: pyrI
Find proteins for P0A7F3 (Escherichia coli (strain K12))
Go to UniProtKB:  P0A7F3
Small Molecules
Ligands 2 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
PAL
Query on PAL

Download SDF File 
Download CCD File 
A, C
N-(PHOSPHONACETYL)-L-ASPARTIC ACID
C6 H10 N O8 P
ZZKNRXZVGOYGJT-VKHMYHEASA-N
 Ligand Interaction
ZN
Query on ZN

Download SDF File 
Download CCD File 
B, D
ZINC ION
Zn
PTFCDOFLOPIGGS-UHFFFAOYSA-N
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.71 Å
  • R-Value Free: 0.223 
  • R-Value Work: 0.170 
  • Space Group: P 3 2 1
Unit Cell:
Length (Å)Angle (°)
a = 122.116α = 90.00
b = 122.116β = 90.00
c = 155.928γ = 120.00
Software Package:
Software NamePurpose
CNSrefinement
SDMSdata reduction
CNSphasing
SDMSdata collection
SDMSdata scaling

Structure Validation

View Full Validation Report or Ramachandran Plots



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2005-05-24
    Type: Initial release
  • Version 1.1: 2008-04-30
    Type: Version format compliance
  • Version 1.2: 2011-07-13
    Type: Derived calculations, Version format compliance