Fig. 3: CoxG carries MQ9 within its hydrophobic cavity.

a, An AlphaFold2 (ref. ⁴⁶) model of CoxG showing its CoxG_CT, cytosolic linker and CoxG_NT. b, Cartoon representation of the X-ray crystal structure of CoxG_NT showing the β-sheet and two α-helices that form the SRPBCC fold, with rainbow coloring from the N terminus (blue) to C terminus (red). c, Surface rendering of the inner hydrophobic cavity of CoxG_NT. The electrostatic potential of the cavity is shown by blue, white and red coloring. d, Stick representation of the hydrophobic residues that line the inner cavity of CoxG_NT. e, Stick representation of key positively charged residues present on the N-terminal side of CoxG_NT. f, Electrostatic surface potential of CoxG_NT mapped onto the surface rendering of the structure. Positively charged regions are blue and negatively charged regions are red, with neutral charge in white. g, Schematic of the experiment performed to test CoxG_NT mediated extraction of MQ9 from M. smegmatis membranes. h, Base peak chromatograms (m/z = 750–2,000) for the high-performance liquid chromatography–mass spectrometry analysis of Folch extracts from CoxG_NT. A substantial peak at 24.14 min is uniquely observed in the M. smegmatis membrane-incubated sample and the corresponding positive mode mass spectrum is shown in i. This shows a single dominant ion at m/z = 804.665, consistent with the ammonium adduct of DH-MQ9 (m/z = 804.665). j, A 2F_o − F_c composite omit map of electron density corresponding to a lipid-like molecule within the hydrophobic cavity of the crystal structure of CoxG_NT contoured at 1σ. k, Molecular docking of MQ9 within the CoxG_NT internal cavity, showing the highest-ranked solution.