title: Extracellular loop C of NPC1L1 is important for binding to ezetimibe.
abstract: Niemann-Pick C1-like protein (NPC1L1) mediates the absorption of dietary cholesterol in the proximal region of the intestine, a process that is blocked by cholesterol absorption inhibitors (CAIs), including ezetimibe (EZE). Using a proteomic approach, we demonstrate that NPC1L1 is the protein to which EZE and its analogs bind. Next, we determined the site of interaction of EZE analogs with NPC1L1 by exploiting the different binding affinities of mouse and dog NPC1L1 for the radioligand analog of EZE, [(3)H]AS. Chimeric and mutational studies indicate that high-affinity binding of [(3)H]AS to dog NPC1L1 depends on molecular determinants present in a 61-aa region of a large extracellular domain (loop C), where Phe-532 and Met-543 appear to be key contributors. These data suggest that the [(3)H]AS-binding site resides in the intestinal lumen and are consistent with preclinical data demonstrating in vivo efficacy of a minimally bioavailable CAI. Furthermore, these determinants of [(3)H]AS binding lie immediately adjacent to a hotspot of human NPC1L1 polymorphisms correlated with hypoabsorption of cholesterol. These observations, taken together with the recently described binding of cholesterol to the N terminus (loop A) of the close NPC1L1 homologue, NPC1, may provide a molecular basis for understanding EZE inhibition of NPC1L1-mediated cholesterol absorption. Specifically, EZE binding to an extracellular site distinct from where cholesterol binds prevents conformational changes in NPC1L1 that are necessary for the translocation of cholesterol across the membrane.
authors.affiliation: Departments of Ion Channels, Medicinal Chemistry, and Pharmacology, Merck Research Laboratories, P.O. Box 2000, Rahway, NJ 07065, USA. adam_weinglass@merck.com
authors.forename: Adam B
authors.initials: AB
authors.lastname: Weinglass
authors.forename: Martin
authors.initials: M
authors.lastname: Kohler
authors.forename: Uwe
authors.initials: U
authors.lastname: Schulte
authors.forename: Jessica
authors.initials: J
authors.lastname: Liu
authors.forename: Emmanuel O
authors.initials: EO
authors.lastname: Nketiah
authors.forename: Anu
authors.initials: A
authors.lastname: Thomas
authors.forename: William
authors.initials: W
authors.lastname: Schmalhofer
authors.forename: Brande
authors.initials: B
authors.lastname: Williams
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bildl
authors.forename: Daniel R
authors.initials: DR
authors.lastname: McMasters
authors.forename: Kevin
authors.initials: K
authors.lastname: Dai
authors.forename: Lindsey
authors.initials: L
authors.lastname: Beers
authors.forename: Margaret E
authors.initials: ME
authors.lastname: McCann
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Kaczorowski
authors.forename: Maria L
authors.initials: ML
authors.lastname: Garcia
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D001384:Azetidines / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D001693:Biological Transport, Active / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002791:Cholesterol, Dietary / Q000378:metabolism*; D004285:Dogs; D000069438:Ezetimibe; D007408:Intestinal Absorption / Q000187:drug effects / Q000235:genetics; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D011110:Polymorphism, Genetic; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D040901:Proteomics / Q000379:methods
chemical_list: D000924:Anticholesteremic Agents; D001384:Azetidines; D002791:Cholesterol, Dietary; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C410800:NPC1L1 protein, human; C482445:Npc1l1 protein, mouse; D000069438:Ezetimibe