A Systematic Investigation of Structure/Function Requirements for the Apolipoprotein A-I/Lecithin Cholesterol Acyltransferase Interaction Loop of High-density Lipoprotein

Abstract

The interaction of lecithin-cholesterol acyltransferase (LCAT) with apolipoprotein A-I (apoA-I) plays a critical role in highdensity lipoprotein (HDL) maturation. We previously identified a highly solvent-exposed apoA-I loop domain (Leu 159 Apolipoprotein A-I (apoA-I), the major protein component of high-density lipoprotein (HDL), transports lipids and also serves as a protein scaffold for numerous HDL-associated protein interactions. The HDL particle is responsible for facilitating reverse cholesterol transport, a multistep process that removes cholesterol from peripheral tissues and ultimately from the body in feces. To promote its cholesterol carrier functions, apoA-I exists in multiple forms throughout the reverse cholesterol transport process. Initially, lipid-free or lipid-poor apoA-I becomes lipidated, generating the nascent HDL particle via the ATP-binding cassette transporter type 1 (ABCA1) 4 (1-4). Although capable of facilitating reverse cholesterol transport, subsequent maturation of the HDL particle into a cholesteryl ester-laden spherical particle substantially increases the capacity of the HDL particle to carry cholesterol cargo. Lecithin-cholesterol acyltransferase (LCAT) is the primary enzyme responsible for catalyzing the maturation of nascent HDL into spherical HDL by catalyzing esterification of free cholesterol (1). Fielding and colleagues (5) first showed that apoA-I within nascent HDL stimulates LCAT activity (5-7). The mechanism by which LCAT facilitates HDL maturation at the structural level is still unknown.-

Interaction of lecithin-cholesterol acyltransferase with lipid surfaces and apolipoprotein A-I derived peptides: implications for the cofactor mechanism of apolipoprotein A-I

“…These findings agree with previous experimental reports showing that apoA-I increases the binding of LCAT to lipids compared to apolipoprotein-free small unilamellar vesicles (Jin et al, 1999;Jonas, 2000). Earlier it has been shown that the apoA-I mutation Y166F decreases the surface binding and activity of LCAT which is in agreement with our experimental results (Gu et al, 2016;Wu et al, 2007). In general, many studies have pointed out that the charged and polar amino acids located in the central parts of apoA-I are important in LCAT activity (Sorci-Thomas et al, 2009;Sorci-Thomas and Thomas, 2002).…”

A retractable lid in lecithin:cholesterol acyltransferase provides a structural mechanism for activation by apolipoprotein A-I

“…S5, and Table 2). The K d of 0.72 M obtained for WT LCAT is consistent with previous studies (14,38,39). ⌬N⌬C was the most defective in this analysis, decreasing the K d value by an order of magnitude, consistent with a role for the N terminus in HDL binding.…”

A thumbwheel mechanism for APOA1 activation of LCAT activity in HDL[S]

“…We measured the binding of varying concentrations of LCAT to immobilized rHDL substrates to determine equilibrium binding constants. Figure 6 shows that LCAT bound to WT rHDL with a K D of 1.9-2.1 M, consistent with previous reports (46). K133C rHDL exhibited a similar K D of 0.7 M.…”