出版社：American Society for Biochemistry and Molecular Biology
摘要：Scavenger receptor class B type I (SR-BI) facilitates the uptakeof HDL cholesteryl esters (CEs) in a two-step process involvingbinding of HDL to its extracellular domain and transfer of HDLcore CEs to a metabolically active membrane pool, where theyare subsequently hydrolyzed by a neutral CE hydrolase. Recently,we characterized a mutant, G420H, which replaced glycine 420in the extracellular domain of SR-BI with a histidine residueand had a profound effect on SR-BI function. The G420H mutantreceptor exhibited a reduced ability to mediate selective HDLCE uptake and was unable to deliver HDL CE for hydrolysis, despitethe fact that it retained the ability to bind HDL. This didnot hold true if glycine 420 was replaced with an alanine residue;G420A maintained wild-type HDL binding and cholesterol transportactivity. To further understand the role that glycine 420 playsin SR-BI function and why there was a disparity between replacingglycine 420 with a histidine versus an alanine, we generateda battery of point mutants by substituting glycine 420 withamino acids possessing side chains that were charged, hydrophobic,polar, or bulky and tested the resulting mutants for their abilityto support HDL binding, HDL cholesterol transport, and deliveryfor hydrolysis. The results indicated that substitution witha negatively charged residue or a proline impaired cell surfaceexpression of SR-BI or its interaction with HDL, respectively.Furthermore, substitution of glycine 420 with a positively chargedresidue reduced HDL CE uptake as well as its subsequent hydrolysis.Supplementary key words high density lipoprotein • scavenger receptor class B type I • selective uptake • cholesteryl ester metabolism • free cholesterol • reverse cholesterol transport
Abbreviations: apoA-I, apolipoprotein A-I; BLT-1, blocks lipid transport-1; CE, cholesteryl ester; COE, cholesteryl oleyl ether; FC, free cholesterol; SR-BI, scavenger receptor class B type I
