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The crystal structure of human apolipoprotein A-I in complex with Fab 55201
Structural highlights
DiseaseAPOA1_HUMAN Defects in APOA1 are a cause of high density lipoprotein deficiency type 2 (HDLD2) [MIM:604091; also known as familial hypoalphalipoproteinemia (FHA). Inheritance is autosomal dominant.[1] [2] Defects in APOA1 are a cause of the low HDL levels observed in high density lipoprotein deficiency type 1 (HDLD1) [MIM:205400; also known as analphalipoproteinemia or Tangier disease (TGD). HDLD1 is a recessive disorder characterized by the absence of plasma HDL, accumulation of cholesteryl esters, premature coronary artery disease, hepatosplenomegaly, recurrent peripheral neuropathy and progressive muscle wasting and weakness. In HDLD1 patients, ApoA-I fails to associate with HDL probably because of the faulty conversion of pro-ApoA-I molecules into mature chains, either due to a defect in the converting enzyme activity or a specific structural defect in Tangier ApoA-I.[3] [4] Note=A mutation in APOA1 is the cause of amyloid polyneuropathy-nephropathy Iowa type (AMYLIOWA); also known as amyloidosis van Allen type or familial amyloid polyneuropathy type III. AMYLIOWA is a hereditary generalized amyloidosis due to deposition of amyloid mainly constituted by apolipoprotein A1. The clinical picture is dominated by neuropathy in the early stages of the disease and nephropathy late in the course. Death is due in most cases to renal amyloidosis. Severe peptic ulcer disease can occurr in some and hearing loss is frequent. Cataracts is present in several, but vitreous opacities are not observed.[5] [6] [7] [8] Defects in APOA1 are a cause of amyloidosis type 8 (AMYL8) [MIM:105200; also known as systemic non-neuropathic amyloidosis or Ostertag-type amyloidosis. AMYL8 is a hereditary generalized amyloidosis due to deposition of apolipoprotein A1, fibrinogen and lysozyme amyloids. Viscera are particularly affected. There is no involvement of the nervous system. Clinical features include renal amyloidosis resulting in nephrotic syndrome, arterial hypertension, hepatosplenomegaly, cholestasis, petechial skin rash.[9] [10] [11] FunctionAPOA1_HUMAN Participates in the reverse transport of cholesterol from tissues to the liver for excretion by promoting cholesterol efflux from tissues and by acting as a cofactor for the lecithin cholesterol acyltransferase (LCAT). As part of the SPAP complex, activates spermatozoa motility.[12] Publication Abstract from PubMedApolipoprotein A-I (apoA-I) plays important roles in clearing cholesterol and phospholipids from peripheral tissues, forming high-density lipoprotein (HDL). However, despite this important function, apoA-I has a propensity to form amyloid fibrils implicated in atherosclerosis and hereditary amyloidosis. Historically, structural determination of lipid-free or lipid-poor apoA-I has been difficult. Here, we obtained the crystal structure of the apoA-I monomer in complex with the antigen-binding fragment (Fab) of a monoclonal antibody. The structure reveals that the N-terminal domain (NTD, residues 1-184) of apoA-I is a compact four-helical bundle, whereas the C-terminal domain (CTD, residues 185-243) is unresolved in the structure. Molecular Dynamics (MD) simulations and small-angle X-ray scattering (SAXS) analysis revealed that the apoA-I NTD dimerises by domain-swapping and the dimer is elongated. Methionine (Met) oxidation in apoA-I destabilises both full-length apoA-I (apoA-I(FL)) and C-terminally truncated apoA-I (apoA-I(Delta185-243)), causing dissociation of the domain-swapped dimer and fibril formation. Met oxidation also increased the lipid-binding ability of apoA-I(Delta185-243), while the amyloidogenic mutation, G26R, did not. Hydrogen-deuterium exchange coupled with nuclear magnetic resonance (HDX-NMR), SAXS, and MD analyses showed that triply Met-oxidised (3MetO) and G26R apoA-I(Delta185-243) are both highly dynamic but remain partially folded. Based on these results, we propose that domain-swapping dimerisation also exists in apoA-I(FL), with the CTD mediating further oligomerisation. We also propose that lipid-binding is promoted by increased global destabilisation in the protein structure, and/or driven by a specific local conformation that is induced by Met-oxidation but not the G26R mutation. The structure of the apolipoprotein A-I monomer provides insights into its oligomerisation and lipid-binding mechanisms.,Tou HI, Rosenes Z, Khandokar Y, Zlatic C, Metcalfe R, Mok YF, Morton CJ, Gooley PR, Griffin MDW J Mol Biol. 2025 Aug 13:169394. doi: 10.1016/j.jmb.2025.169394. PMID:40816717[13] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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