Figure 1.

Structures of BtuCD-F and ModBC-A and Their Respective Mass Spectra

(A) X-ray crystal structures of BtuCD-F (left, PDB: 2QI9) and ModBC-A (right, PDB: 2ONK) visualized using PyMol (Schrödinger).

(B) Mass spectrum of BtuCD-F reveals a charge state series consistent with the mass of the tetrameric transporter (BtuC₂D₂) bound to the SBP (BtuF) (BtuC₂D₂-F) a smaller population of uncomplexed transporter (BtuC₂D₂ red peaks) is also apparent. Different lipid species, primarily LPS, are bound to the transporter both in the presence and the absence of the SBP (light blue peaks).

(C) Mass spectrum of ModBC-A shows a charge state series consistent with the tetrameric transporter bound to SBP and molybdate with different lipid-bound species primarily LPS (light blue peaks). Theoretical and observed molecular masses of all species are presented in Table 1.