Protein‐Protein and Protein‐Detergent Interactions of the Burkholderia Type III Secretion System Protein BipC

Abstract

The Type III Secretion System (T3SS) is an essential component of pathogenesis in many Gramnegative bacteria, including Burkholderia pseudomallei, the causative agent of melioidosis. T3SS structural components assemble into a needle apparatus that facilitates injection of virulence factors into a host. Four main parts comprise this needle: a base that spans both bacterial membranes, a needle that protrudes from the base, a needle tip that contacts the host, and a translocon pore that forms in the host cell membrane. Minor translocon protein BipC from B. pseudomallei is believed to be an integral membrane protein that interacts with major translocon protein BipB, tip protein BipD, and chaperone BicA. However, interactions between BipC, its binding partners, and the membrane itself remain uncharacterized. Here we characterized interactions of BipC with detergent micelles and BicA/BipD using circular dichroism spectroscopy (CD) and transverse relaxation‐optimized spectroscopy (TROSY) respectively. Far‐UV CD spectra indicate that BipC normally exists in a partially folded state in solution, but adopts a distinctly alpha‐helical conformation upon titration with various detergents, suggesting that BipC becomes embedded in detergent micelles. [15N,1H]‐TROSY spectra of BipC titrated with either BicA or BipD revealed sites of interaction predominantly restricted to N‐terminal domain of BipC. In conclusion, our results suggest that BipC inserts into membranes and primarily interacts with its binding partners via its N‐terminal domain. These findings will help elucidate the mechanism of T3SS translocon assembly and the structural changes that occur within its components.Support or Funding InformationWe would like to thank the other members of De Guzman Lab, as well as Dr. JustinDouglas and Dr. Minli Xing from the KU NMR facility for their support and insight. Research reported here was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, as well as by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant numbers R01AI074856 and P20GM103418 respectively. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Allergy and Infectious Diseases, the National Institute of General Medical Sciences, or the National Institutes of Health.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.