1xge
From Proteopedia
Dihydroorotase from Escherichia coli: Loop Movement and Cooperativity between subunits
Overview
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.
About this Structure
1XGE is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Dihydroorotase from Escherichia coli: loop movement and cooperativity between subunits., Lee M, Chan CW, Mitchell Guss J, Christopherson RI, Maher MJ, J Mol Biol. 2005 May 6;348(3):523-33. PMID:15826651 Page seeded by OCA on Sat May 3 14:59:45 2008
