LCAT-Remodeled Structural Transition of Reconstituted HDL Enhances SR-BI Binding

Reconstituted high-density lipoprotein (rHDL) particles adopt distinct structural states, yet how these states influence receptor recognition remains incompletely understood. Here, we compared the structural features of discoidal rHDL and LCAT-remodeled spherical-like rHDL model particles and evaluated their interactions with scavenger receptor class B type I (SR-BI). Recombinant apolipoprotein A-I (ApoA-I) was expressed and used to assemble discoidal rHDL, which was subsequently converted into spherical-like rHDL through lecithin-cholesterol acyltransferase (LCAT)-mediated remodeling. Agarose gel electrophoresis, transmission electron microscopy, and 1H–15N HSQC NMR spectroscopy confirmed that the two rHDL species differed in electrophoretic mobility, morphology, size distribution, and ApoA-I spectral properties. In particular, ApoA-I in discoidal rHDL exhibited greater NMR visibility than in LCAT-remodeled spherical-like rHDL, consistent with distinct conformational and dynamic states. Biolayer interferometry further showed that LCAT-remodeled spherical-like rHDL model particles bound SR-BI with substantially higher apparent affinity than discoidal rHDL. Together, these findings demonstrate that the structural state of rHDL strongly influences its interaction with SR-BI and support a model in which the LCAT-remodeled structural transition of rHDL is accompanied by ApoA-I reorganization that favors receptor binding. This study provides mechanistic insight into how structural changes in model rHDL particles modulate receptor engagement.