| Abstract: |
In our quest to develop new compounds to block a range of infections, we have been studying a bacterial protein called AdhE. AdhE is important because when it is deleted from pathogenic E. coli (strain O157:H7) it causes a huge attenuation of virulence and a reduction in expression of the major system used to attach to host cells. Unusually, AdhE oligomerises in vivo and in vitro to form long (15-120 nm) filaments, called spirosomes, that can be visualised using electron microscopy. Understanding how AdhE spirosomes work will help us to develop, in the longer-term, specific inhibitors that might function against a range of Gram-negative pathogens.
Previously we studied the solution properties of unfractionated, and notoriously heterogeneous, AdhE but the resultant data were difficult to fully interpret. Here, we report progress on understanding the solution behaviour of AdhE in partially fractionated, but still functional, form. Analytical ultracentrifugation (AUC) sedimentation velocity and small angle X-ray scattering (SAXS) analysis of fractionated AdhE demonstrates that it is not possible, with conventional size exclusion chromatography in our hands, to generate homogenous AdhE samples. Instead, we were able to determine the constituents of fractions and building on this, we observed subtle but measurable structural changes consistent with an increase in the AdhE spirosome helical pitch in the presence of enzymatic cofactors, and consistent with our hypothesis that AdhE spirosomes control the channeling of substrates through conformational changes. |
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