Fig. 4.

Integration of XL-MS with the complimentary structural methods of EM and HDX-MS data for the LCAT-HDL complex. a Representation of the inter-protein cross-links. Red spheres indicate reactive amino acids; cross-links within the distance limit (Cα-Cα distance < 40 Å) are shown in yellow, the specific cross-link connecting two LCAT molecules is shown in green, ApoA-I α-helices 6 are presented in cyan, and α-helices 4 and 5 are shown in dark gray. b EM 3D density map. c HDX-MS data presented in the LCAT structure (PDB 6MVD); LCAT regions with decreased deuterium exchange after HDL binding are presented on a scale of blue intensity. Spheres present amino acids involved in the cross-links with ApoA-I. No HDX data were obtained for the regions shown in light green. d Proposed structural model of the LCAT-HDL complex obtained by integrating all experimental data. The figure was adapted from [28]