1XGE

Dihydroorotase from Escherichia coli: Loop Movement and Cooperativity between Subunits

(2005) J Mol Biol 348: 523-533

• PubMed: 15826651 Search on PubMed
• DOI: https://doi.org/10.1016/j.jmb.2005.01.067
• Primary Citation of Related Structures:  
  1XGE


• PubMed Abstract: 
  

  Escherichia coli dihydroorotase has been crystallized in the presence of the product, L-dihydroorotate (L-DHO), and the structure refined at 1.9A resolution. The structure confirms that previously reported (PDB entry 1J79), crystallized in the presence of the substrate N-carbamyl-D,L-aspartate (D, L-CA-asp), which had a dimer in the asymmetric unit, with one subunit having the substrate, L-CA-asp bound at the active site and the other having L-DHO. Importantly, no explanation for the unusual structure was given. Our results now show that a loop comprised of residues 105-115 has different conformations in the two subunits. In the case of the L-CA-asp-bound subunit, this loop reaches in toward the active site and makes hydrogen-bonding contact with the bound substrate molecule. For the L-DHO-bound subunit, the loop faces in the opposite direction and forms part of the surface of the protein. Analysis of the kinetics for conversion of L-DHO to L-CA-asp at low concentrations of L-DHO shows positive cooperativity with a Hill coefficient n=1.57(+/-0.13). Communication between subunits in the dimer may occur via cooperative conformational changes of the side-chains of a tripeptide from each subunit: Arg256-His257-Arg258, near the subunit interface.

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Organizational Affiliation: 

School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales 2006, Australia.