The control of metabolic flux in biosynthetic pathways is critically important to the survival of microorganisms. A common control mechanism for biosynthetic pathway enzymes is allosteric regulation, which is the modulation of the enzyme active site caused by effector binding at a remote site. For adenosine triphosphate phosphoribosyl transferase (ATP-PRT), the first enzyme in the histidine biosynthetic pathway, large conformational changes in the hexameric complex are associated with the binding of histidine, the allosteric effector. But how is the allosteric signal propagated within ATP-PRT to achieve inhibition? We tried to answer this question by studying the changes in motions and conformations of the ATP-PRT enzyme using a combined computational and experimental approach.
The cover image of the May 21 issue of the Biophysical Journal shows the crystal structure of ATP-PRT from Campylobacter jejuni, in a complex with the allosteric ligand histidine and the active site-inhibitor adenosine monophosphate (AMP). The ATP-PRT enzyme is shown in cartoon representation, and the ligands (histidine and AMP) are shown as green spheres. Histidine ligands are located at the top and the bottom at the regulatory domains, while AMP is represented by the two green molecules in the middle, which indicate the location of the active sites. The hexameric complex of ATP-PRT is made up by trimers of dimers. Two of the six chains in the hexameric complex are coloured in blue and gold, in order to highlight the dimers. The other four chains are shown in grey, along with a transparent molecular surface representation.
The major finding of our paper is that the twisting of the active site hinge region is the key for delivering regulated catalysis in ATP-PRT. The cover image highlights the locations of allosteric and active sites on ATP-PRT and gives an impression of the long distance for allosteric signal transmission. It also illustrates the domain arrangements of ATP-PRT, which allows for the multitude of conformational changes required for catalysis and regulation.
Understanding the regulation mechanism of enzyme activities has implications for many other areas of research, such as enzyme evolution, protein engineering and drug discovery. Our study illustrates that combining computational methods with experiments is a powerful approach that can enable comprehension of the molecular basis of enzyme catalysis and regulation at atomic level detail.
- Wanting Jiao, Gert-Jan Moggré, Gerd Mittelstädt, Emily Parker