Structural insights into Escherichia coli polymyxin B resistance protein D with X-ray crystallography and small-angle X-ray scattering

Polymyxin B resistance protein D (PmrD) plays a key role in the polymyxin B-resistance pathway, as it is the signaling protein that can act as a specific connecter between PmrA/PmrB and PhoP/PhoQ. We conducted structural analysis to characterize Escherichia coli (E. coli) PmrD, which exhibits different features compared with PmrD in other bacteria.

The X-ray crystal structure of E. coli PmrD was determined at a 2.00?? resolution, revealing novel information such as the unambiguous secondary structures of the protein and the presence of a disulfide bond. Furthermore, various assays such as native gel electrophoresis, surface plasmon resonance (SPR), size-exclusion chromatography, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) measurements, were performed to elucidate the structural and functional role of the internal disulfide bond in E. coli PmrD.

The structural characteristics of E. coli PmrD were clearly identified via diverse techniques. The findings help explain the different protective mechanism of E. coli compared to other Gram-negative bacteria.