STUDY ON THE HDL::LCAT INTERACTION AND INSIGHTS INTO LCAT PHARMACOLOGICAL MODULATION

Lecithin:cholesterol-acyl-transferase (LCAT) plays a major role in cholesterol metabolism as it is the only extracellular enzyme able to esterify cholesterol. LCAT activity is required for lipoprotein remodeling and, most specifically, for the growth and maturation of HDLs. In fact, genetic alterations affecting LCAT functionality may cause a severe reduction in plasma levels of HDL-cholesterol with important clinical consequences, for which, at present, no optimal treatment is available. Within this project, we ultimately aim at establishing landmarks for future structure-based drug-discovery of novel small-molecule activators able to rescue the defective enzyme in LCAT deficiency patients. To this end, we thoroughly studied the LCAT::HDL recognition and activation mechanism and investigated some aspects of LCAT pharmacological modulation. Although several hypotheses were formulated, the exact molecular recognition mechanism between LCAT and HDLs is still unknown. We employed a combination of structural bioinformatics procedures to deepen the insights into the HDL-LCAT interplay that promotes LCAT activation and cholesterol esterification. We have generated a data-driven model of reconstituted HDL (rHDL) and studied the dynamics of an assembled rHDL::LCAT supramolecular complex, pinpointing the conformational changes originating from the interaction between LCAT and apolipoprotein A-I (apoA-I) that are necessary for LCAT activation. Specifically, we propose a mechanism in which the anchoring of LCAT lid to apoA-I helices allows the formation of a hydrophobic hood that expands LCAT active site and shields it from the solvent, allowing the enzyme to process large hydrophobic substrates. Through the atomistic knowledge gained from our modeling work, we then studied the mechanism-of-action of some members of two known classes of small-molecule LCAT modulators and their interaction with a subset of LCAT mutants, rationalizing the bases for the future design of novel activators characterized by higher efficacy.