title: Mechanism of LDL binding and release probed by structure-based mutagenesis of the LDL receptor.
abstract: The LDL receptor (LDL-R) mediates cholesterol metabolism in humans by binding and internalizing cholesterol transported by LDL. Several different molecular mechanisms have been proposed for the binding of LDL to LDL-R at neutral plasma pH and for its release at acidic endosomal pH. The crystal structure of LDL-R at acidic pH shows that the receptor folds back on itself in a closed form, obscuring parts of the ligand binding domain with the epidermal growth factor (EGF)-precursor homology domain. We have used a structure-based site-directed mutagenesis approach to examine 12 residues in the extracellular domain of LDL-R for their effect on LDL binding and release. Our studies show that the interface between the ligand binding domain and the EGF-precursor homology domain seen at acidic pH buries residues mediating both LDL binding and release. Our results are consistent with an alternative model of LDL-R whereby multiple modules of the extracellular domain interact with LDL at neutral pH, concurrently positioning key residues so that at acidic pH the LDL-R:LDL interactions become unfavorable, triggering release. After LDL release, the closed form of LDL-R may target its return to the cell surface.
authors.affiliation: Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Sha
authors.initials: S
authors.lastname: Huang
authors.forename: Lisa
authors.initials: L
authors.lastname: Henry
authors.forename: Yiu Kee
authors.initials: YK
authors.lastname: Ho
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Pownall
authors.forename: Gabby
authors.initials: G
authors.lastname: Rudenko
mesh_terms: D018360:Crystallography, X-Ray; D004815:Epidermal Growth Factor / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D011973:Receptors, LDL / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D008077:Lipoproteins, LDL; D011973:Receptors, LDL; D004815:Epidermal Growth Factor
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