Method for the Successful Crystallization of the Ferric Uptake Regulator from Campylobacter jejuni

Purification and characterization of Campylobacter jejuni ferric uptake regulator

The ferric uptake regulator (Fur) is a superfamily of transcription factors found in bacteria which control the expression of a myriad of genes. In this study, we report a simple protocol for the purification of recombinant untagged Campylobacter jejuni Fur (CjFur). CjFur was isolated using a combination of three ion exchange chromatography steps followed by size exclusion chromatography on a Superdex 75. ESI-MS analysis shows that our method yields pure CjFur and that this tag-free version incorporates metal more efficiently than recombinant CjFur harboring a tag or tag remnants. Finally, electrophoretic mobility shift assays show that this new purification method yields a CjFur preparation that binds DNA more efficiently. These results suggest that adding a N-terminus tag onto CjFur is detrimental to its activity. Overall, the approaches detailed in this study offer an alternative strategy for the purification of CjFur, and likely other metalloregulators, for future biochemical and biophysical studies.

Structural Analysis of the Ash2L/Dpy-30 Complex Reveals a Heterogeneity in H3K4 Methylation

Dpy-30 is a regulatory subunit controlling the histone methyltransferase activity of the KMT2 enzymes in vivo. Paradoxically, in vitro methyltransferase assays revealed that Dpy-30 only modestly participates in the positive heterotypic allosteric regulation of these methyltransferases. Detailed genome-wide, molecular and structural studies reveal that an extensive network of interactions taking place at the interface between Dpy-30 and Ash2L are critical for the correct placement, genome-wide, of H3K4me2 and H3K4me3 but marginally contribute to the methyltransferase activity of KMT2 enzymes in vitro. Moreover, we show that H3K4me2 peaks persisting following the loss of Dpy-30 are found in regions of highly transcribed genes, highlighting an interplay between Complex of Proteins Associated with SET1 (COMPASS) kinetics and the cycling of RNA polymerase to control H3K4 methylation. Overall, our data suggest that Dpy-30 couples its modest positive heterotypic allosteric regulation of KMT2 methyltransferase activity with its ability to help the positioning of SET1/COMPASS to control epigenetic signaling.

Functional insights into the interplay between DNA interaction and metal coordination in ferric uptake regulators

Ferric uptake regulators (Fur) are a family of transcription factors coupling gene regulatory events to metal concentration. Recent evidence has expanded the mechanistic repertoires employed by Fur to activate or repress gene expression in the presence or absence of regulatory metals. However, the mechanistic basis underlying this extended repertoire has remained largely unexplored. In this study, we used an extensive set of mutations to demonstrate that Campylobacter jejuni Fur (CjFur) employs the same surface to positively and negatively control gene expression regardless of the presence or absence of metals. Moreover, the crystal structure determination of a CjFur devoid of any regulatory metals shows that subtle reorientation of the transcription factor DNA binding domain negatively impacts DNA binding, gene expression and gut colonization in chickens. Overall, these results highlight the versatility of the CjFur DNA binding domain in mediating all gene regulatory events controlled by the metalloregulator and that the full metalation of CjFur is critical to the Campylobacter jejuni life cycle in vivo.