Pressure-induced activation of latent Dihydroorotase from Aquifex aeolicus as revealed by high pressure protein crystallography
Résumé
Dihydroorotase is involved in the de novo synthesis of pyrimidine in virtually all organisms, and it is usually associated with two other enzymes found in this biosynthetic pathway, carbamylphosphate synthetase and/or aspartate transcarbamylase. In the hyperthermophilic bacterium Aquifex aeolicus, aspartate transcarbamylase and dihydroorotase are non-covalently associated. Upon dissociation, aspartate transcarbamylase keeps its activity entirely while dihydroorotase is totally inactivated. It was previously shown that high pressure fully restores the activity of this isolated dihydroorotase. On the basis of kinetic studies, site-directed mutagenesis and the use of peptides mimicking loop A, a loop that appears to block access to the active site, it was proposed that this pressure-induced reactivation was due to the decrease in the volume of the system, -ΔV, resulting from the disruption of known ionic interactions between the loop and the main part of the protein. In the present work, this interpretation is more precisely demonstrated by the determination of the crystallographic structure of isolated dihydroorotase under pressure. In addition to the loop displacements, pressure induces a discrete rearrangement of the catalytic site aspartate 305, an effect that might additionally contribute to the reactivation of this enzyme. This article is protected by copyright. All rights reserved.