Continuous and pulsed hydrogen-deuterium exchange and mass spectrometry characterize CsgE oligomerization

We report the use of hydrogen-deuterium amide exchange coupled to mass spectrometry (HDX-MS) to study the interfaces of and conformational changes accompanying CsgE oligomerization. This protein plays an important role in enteric bacteria biofilm formation. Biofilms provide protection for enteric bacteria from environmental extremes and raise concerns about controlling bacteria and infectious disease. Their proteinaceous components, called curli, are extracellular functional amyloids that initiate surface contact and biofilm formation. The highly regulated curli biogenesis involves a major subunit, CsgA, a minor subunit CsgB, and a series of other accessory proteins. CsgE, possibly functioning as oligomer, is a chaperonin-like protein that delivers CsgA to an outer-membrane bound oligomeric CsgG complex. No higher-order structure, or interfaces and dynamics of its oligomerization, however, are known. In this work, we determined regions involved in CsgE self-association by continuous HDX, and, on the basis of that, prepared a double mutant W48A/F79A, derived from interface alanine scan, and verified that it exists as monomer. Using pulsed HDX and MS, we suggest there is a structural rearrangement occurring during the oligomerization of CsgE.