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Giorgi L, Niemelä A, Kumpula EP, Natri O, Parkkila P, Huiskonen JT, Koivuniemi A. Mechanistic Insights into the Activation of Lecithin-Cholesterol Acyltransferase in Therapeutic Nanodiscs Composed of Apolipoprotein A-I Mimetic Peptides and Phospholipids. Mol Pharm 2022; 19:4135-4148. [PMID: 36111986 PMCID: PMC9644404 DOI: 10.1021/acs.molpharmaceut.2c00540] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 09/08/2022] [Accepted: 09/08/2022] [Indexed: 11/28/2022]
Abstract
The mechanistic details behind the activation of lecithin-cholesterol acyltransferase (LCAT) by apolipoprotein A-I (apoA-I) and its mimetic peptides are still enigmatic. Resolving the fundamental principles behind LCAT activation will facilitate the design of advanced HDL-mimetic therapeutic nanodiscs for LCAT deficiencies and coronary heart disease and for several targeted drug delivery applications. Here, we have combined coarse-grained molecular dynamics simulations with complementary experiments to gain mechanistic insight into how apoA-Imimetic peptide 22A and its variants tune LCAT activity in peptide-lipid nanodiscs. Our results highlight that peptide 22A forms transient antiparallel dimers in the rim of nanodiscs. The dimerization tendency considerably decreases with the removal of C-terminal lysine K22, which has also been shown to reduce the cholesterol esterification activity of LCAT. In addition, our simulations revealed that LCAT prefers to localize to the rim of nanodiscs in a manner that shields the membrane-binding domain (MBD), αA-αA', and the lid amino acids from the water phase, following previous experimental evidence. Meanwhile, the location and conformation of LCAT in the rim of nanodiscs are spatially more restricted when the active site covering the lid of LCAT is in the open form. The average location and spatial dimensions of LCAT in its open form were highly compatible with the electron microscopy images. All peptide 22A variants studied here had a specific interaction site in the open LCAT structure flanked by the lid and MBD domain. The bound peptides showed different tendencies to form antiparallel dimers and, interestingly, the temporal binding site occupancies of the peptide variants affected their in vitro ability to promote LCAT-mediated cholesterol esterification.
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Affiliation(s)
- Laura Giorgi
- Division
of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
| | - Akseli Niemelä
- Division
of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
| | - Esa-Pekka Kumpula
- Institute
of Biotechnology, Helsinki Institute of Life Science (HiLIFE), University of Helsinki, Helsinki 00014, Finland
| | - Ossi Natri
- Division
of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
| | - Petteri Parkkila
- Division
of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
- Division
of Nano and Biophysics, Department of Physics, Chalmers University of Technology, Goteborg 412 96, Sweden
| | - Juha T. Huiskonen
- Institute
of Biotechnology, Helsinki Institute of Life Science (HiLIFE), University of Helsinki, Helsinki 00014, Finland
| | - Artturi Koivuniemi
- Division
of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
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2
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Positive allosteric modulators of lecithin: Cholesterol acyltransferase adjust the orientation of the membrane-binding domain and alter its spatial free energy profile. PLoS Comput Biol 2021; 17:e1008426. [PMID: 33720934 PMCID: PMC7993845 DOI: 10.1371/journal.pcbi.1008426] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 03/25/2021] [Accepted: 02/27/2021] [Indexed: 11/29/2022] Open
Abstract
Lecithin:cholesterol acyltransferase protein (LCAT) promotes the esterification reaction between cholesterol and phospholipid-derived acyl chains. Positive allosteric modulators have been developed to treat LCAT deficiencies and, plausibly, also cardiovascular diseases in the future. The mechanism of action of these compounds is poorly understood. Here computational docking and atomistic molecular dynamics simulations were utilized to study the interactions between LCAT and the activating compounds. Results indicate that all drugs bind to the allosteric binding pocket in the membrane-binding domain in a similar fashion. The presence of the compounds in the allosteric site results in a distinct spatial orientation and sampling of the membrane-binding domain (MBD). The MBD’s different spatial arrangement plausibly affects the lid’s movement from closed to open state and vice versa, as suggested by steered molecular dynamics simulations. High-density lipoprotein (HDL) particles play a crucial role in reverse cholesterol transport, whose efficiency is linked to the development of coronary heart disease (CHD), a global health threat showing an increased prevalence in industrial as well as in developing countries. While many drugs for treating CHD exist, e.g., the cholesterol-lowering statins, a substantial residual vascular risk remains, thus calling for novel therapeutic interventions. One of these approaches is to elevate the activity of lecithin:cholesterol acyltransferase (LCAT) enzyme by, e.g., positive allosteric modulators. However, although modulators’ allosteric binding site is known, it is not understood how these compounds can promote the activity LCAT. Therefore, in this article, we aimed to clarify how a set of positive allosteric modulators affect the structural and dynamical properties of LCAT utilizing atomistic molecular dynamics simulations and free energy calculations. Shortly, our findings suggest that the reorientation and the different energetic landscape of the MBD induced by the allosteric compounds may facilitate the lid’s opening, therefore providing a plausible explanation of why the set of positive allosteric modulators promote the activity of LCAT. Besides, this finding is also insightful when deciphering how apoA-I, the principal LCAT activating apolipoprotein in HDL particles, facilitates the activation of LCAT.
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Casteleijn MG, Parkkila P, Viitala T, Koivuniemi A. Interaction of lecithin:cholesterol acyltransferase with lipid surfaces and apolipoprotein A-I-derived peptides. J Lipid Res 2018; 59:670-683. [PMID: 29438987 PMCID: PMC5880497 DOI: 10.1194/jlr.m082685] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 01/22/2018] [Indexed: 12/12/2022] Open
Abstract
LCAT is an enzyme responsible for the formation of cholesteryl esters from unesterified cholesterol (UC) and phospholipid (PL) molecules in HDL particles. However, it is poorly understood how LCAT interacts with lipoproteins and how apoA-I activates it. Here we have studied the interactions between LCAT and lipids through molecular simulations. In addition, we studied the binding of LCAT to apoA-I-derived peptides, and their effect on LCAT lipid association-utilizing experiments. Results show that LCAT anchors itself to lipoprotein surfaces by utilizing nonpolar amino acids located in the membrane-binding domain and the active site tunnel opening. Meanwhile, the membrane-anchoring hydrophobic amino acids attract cholesterol molecules next to them. The results also highlight the role of the lid-loop in the lipid binding and conformation of LCAT with respect to the lipid surface. The apoA-I-derived peptides from the LCAT-activating region bind to LCAT and promote its lipid surface interactions, although some of these peptides do not bind lipids individually. The transfer free-energy of PL from the lipid bilayer into the active site is consistent with the activation energy of LCAT. Furthermore, the entry of UC molecules into the active site becomes highly favorable by the acylation of SER181.
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Affiliation(s)
- Marco G Casteleijn
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
| | - Petteri Parkkila
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
| | - Tapani Viitala
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
| | - Artturi Koivuniemi
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
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4
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Piper DE, Romanow WG, Gunawardane RN, Fordstrom P, Masterman S, Pan O, Thibault ST, Zhang R, Meininger D, Schwarz M, Wang Z, King C, Zhou M, Walker NPC. The high-resolution crystal structure of human LCAT. J Lipid Res 2015. [PMID: 26195816 DOI: 10.1194/jlr.m059873] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
LCAT is intimately involved in HDL maturation and is a key component of the reverse cholesterol transport (RCT) pathway which removes excess cholesterol molecules from the peripheral tissues to the liver for excretion. Patients with loss-of-function LCAT mutations exhibit low levels of HDL cholesterol and corneal opacity. Here we report the 2.65 Å crystal structure of the human LCAT protein. Crystallization required enzymatic removal of N-linked glycans and complex formation with a Fab fragment from a tool antibody. The crystal structure reveals that LCAT has an α/β hydrolase core with two additional subdomains that play important roles in LCAT function. Subdomain 1 contains the region of LCAT shown to be required for interfacial activation, while subdomain 2 contains the lid and amino acids that shape the substrate binding pocket. Mapping the naturally occurring mutations onto the structure provides insight into how they may affect LCAT enzymatic activity.
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Affiliation(s)
- Derek E Piper
- Therapeutic Discovery Amgen Inc., South San Francisco, CA 94080
| | | | | | | | | | - Oscar Pan
- Therapeutic Discovery, Amgen Inc., Burnaby, BC V5A1V7, Canada
| | | | - Richard Zhang
- Therapeutic Discovery Amgen Inc., South San Francisco, CA 94080
| | | | - Margrit Schwarz
- Metabolic Disorders, Amgen Inc., South San Francisco, CA 94080
| | - Zhulun Wang
- Therapeutic Discovery Amgen Inc., South San Francisco, CA 94080
| | - Chadwick King
- Therapeutic Discovery, Amgen Inc., Burnaby, BC V5A1V7, Canada
| | - Mingyue Zhou
- Metabolic Disorders, Amgen Inc., South San Francisco, CA 94080
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5
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Sensi C, Simonelli S, Zanotti I, Tedeschi G, Lusardi G, Franceschini G, Calabresi L, Eberini I. Distant homology modeling of LCAT and its validation through in silico targeting and in vitro and in vivo assays. PLoS One 2014; 9:e95044. [PMID: 24736652 PMCID: PMC3988154 DOI: 10.1371/journal.pone.0095044] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 03/23/2014] [Indexed: 11/18/2022] Open
Abstract
LCAT (lecithin:cholesterol acyltransferase) catalyzes the transacylation of a fatty acid of lecithin to cholesterol, generating a cholesteryl ester and lysolecithin. The knowledge of LCAT atomic structure and the identification of the amino acids relevant in controlling its structure and function are expected to be very helpful to understand the enzyme catalytic mechanism, as involved in HDL cholesterol metabolism. However - after an early report in the late ‘90 s - no recent advance has been made about LCAT three-dimensional structure. In this paper, we propose an LCAT atomistic model, built following the most up-to-date molecular modeling approaches, and exploiting newly solved crystallographic structures. LCAT shows the typical folding of the α/β hydrolase superfamily, and its topology is characterized by a combination of α-helices covering a central 7-strand β-sheet. LCAT presents a Ser/Asp/His catalytic triad with a peculiar geometry, which is shared with such other enzyme classes as lipases, proteases and esterases. Our proposed model was validated through different approaches. We evaluated the impact on LCAT structure of some point mutations close to the enzyme active site (Lys218Asn, Thr274Ala, Thr274Ile) and explained, at a molecular level, their phenotypic effects. Furthermore, we devised some LCAT modulators either designed through a de novo strategy or identified through a virtual high-throughput screening pipeline. The tested compounds were proven to be potent inhibitors of the enzyme activity.
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Affiliation(s)
- Cristina Sensi
- Laboratorio di Biochimica e Biofisica Computazionale, Università degli Studi di Milano, Milano, Italia
| | - Sara Simonelli
- Centro Enrica Grossi Paoletti, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Milano, Italia
| | - Ilaria Zanotti
- Dipartimento di Farmacia, Università Degli Studi di Parma, Parma, Italia
| | - Gabriella Tedeschi
- Dipartimento di Scienze Veterinarie e Sanità Pubblica, Università degli Studi di Milano, Milano, Italia
| | - Giulia Lusardi
- Dipartimento di Farmacia, Università Degli Studi di Parma, Parma, Italia
| | - Guido Franceschini
- Centro Enrica Grossi Paoletti, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Milano, Italia
| | - Laura Calabresi
- Centro Enrica Grossi Paoletti, Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Milano, Italia
| | - Ivano Eberini
- Laboratorio di Biochimica e Biofisica Computazionale, Università degli Studi di Milano, Milano, Italia
- * E-mail:
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6
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Naito S, Kamata M, Furuya M, Hayashi M, Kuroda M, Bujo H, Kamata K. Amelioration of circulating lipoprotein profile and proteinuria in a patient with LCAT deficiency due to a novel mutation (Cys74Tyr) in the lid region of LCAT under a fat-restricted diet and ARB treatment. Atherosclerosis 2013; 228:193-7. [DOI: 10.1016/j.atherosclerosis.2013.02.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 01/31/2013] [Accepted: 02/26/2013] [Indexed: 12/22/2022]
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Group XV phospholipase A₂, a lysosomal phospholipase A₂. Prog Lipid Res 2010; 50:1-13. [PMID: 21074554 DOI: 10.1016/j.plipres.2010.10.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Revised: 10/29/2010] [Accepted: 10/30/2010] [Indexed: 12/21/2022]
Abstract
A phospholipase A₂ was identified from MDCK cell homogenates with broad specificity toward glycerophospholipids including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol. The phospholipase has the unique ability to transacylate short chain ceramides. This phospholipase is calcium-independent, localized to lysosomes, and has an acidic pH optimum. The enzyme was purified from bovine brain and found to be a water-soluble glycoprotein consisting of a single peptide chain with a molecular weight of 45 kDa. The primary structure deduced from the DNA sequences is highly conserved between chordates. The enzyme was named lysosomal phospholipase A₂ (LPLA₂) and subsequently designated group XV phospholipase A₂. LPLA₂ has 49% of amino acid sequence identity to lecithin-cholesterol acyltransferase and is a member of the αβ-hydrolase superfamily. LPLA₂ is highly expressed in alveolar macrophages. A marked accumulation of glycerophospholipids and extensive lamellar inclusion bodies, a hallmark of cellular phospholipidosis, is observed in alveolar macrophages in LPLA₂(-/-) mice. This defect can also be reproduced in macrophages that are exposed to cationic amphiphilic drugs such as amiodarone. In addition, older LPLA₂(-/-) mice develop a phenotype similar to human autoimmune disease. These observations indicate that LPLA₂ may play a primary role in phospholipid homeostasis, drug toxicity, and host defense.
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8
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Sorci-Thomas MG, Bhat S, Thomas MJ. Activation of lecithin:cholesterol acyltransferase by HDL ApoA-I central helices. CLINICAL LIPIDOLOGY 2009; 4:113-124. [PMID: 20582235 PMCID: PMC2891274 DOI: 10.2217/17584299.4.1.113] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is an enzyme that first hydrolyzes the sn-2 position of phospholipids, preferentially a diacylphosphocholine, and then transfers the fatty acid to cholesterol to yield a cholesteryl ester. HDL ApoA-I is the principal catalytic activator for LCAT. Activity of LCAT on nascent or lipid-poor HDL particles composed of phospholipid, cholesterol and ApoA-I allows the maturation of HDL particles into lipid-rich spherical particles that contain a core of cholesteryl ester surrounded by phospholipid and ApoA-I on the surface. This article reviews the recent progress in elucidating structural aspects of the interaction between LCAT and ApoA-I. In the last decade, there has been considerable progress in understanding the structure of ApoA-I and the central helices 5, 6, and 7 that are known to activate LCAT. However, much less information has been forthcoming describing the 3D structure and conformation of LCAT required to catalyze two separate reactions within a single monomeric peptide.
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Affiliation(s)
- Mary G Sorci-Thomas
- Department of Pathology, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1016, USA, Tel.: +1 336 716 2147, Fax: +1 336 716 6279,
| | - Shaila Bhat
- Department of Pathology, Lipid Sciences Research Center, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA, Tel.: +1 336 716 6062, Fax: +1 336 716 6279,
| | - Michael J Thomas
- Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA, Tel.: +1 336 716 2313, Fax: +1 336 716 6279,
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9
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Doke AM, Mathur SK, Sadana A. Fractal Binding and Dissociation Kinetics of Heart-Related Compounds on Biosensor Surfaces. J Recept Signal Transduct Res 2008; 26:337-57. [PMID: 16818380 DOI: 10.1080/10799890600754889] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A fractal analysis is presented for the binding and dissociation of different heart-related compounds in solution to receptors immobilized on biosensor surfaces. The data analyzed include LCAT (lecithin cholesterol acyl transferase) concentrations in solution to egg white apoA-I rHDL immobilized on a biosensor chip surface (1), native, mildly oxidized, and strongly oxidized LDL in solution to a heparin-modified Au-surface of a surface plasmon resonance (SPR) biosensor (2), and TRITC-labeled HDL in solution to a bare optical fiber surface (3). Single-and dual-fractal models were used to fit the data. Values of the binding and the dissociation rate coefficient(s), affinity values, and the fractal dimensions were obtained from the regression analysis provided by Corel Quattro Pro 8.0 (4). The binding rate coefficients are quite sensitive to the degree of heterogeneity on the sensor chip surface. Predictive equations are developed for the binding rate coefficient as a function of the degree of heterogeneity present on the sensor chip surface and on the LCAT concentration in solution and for the affinity as a function of the ratio of fractal dimensions present in the binding and the dissociation phases. The analysis presented provided physical insights into these analyte-receptor reactions occurring on different biosensor surfaces.
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Affiliation(s)
- Atul M Doke
- Chemical Engineering Department, University of Mississippi, University, Mississippi 38677-184, USA
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Reshetnyak Y, Tchedre KT, Nair MP, Pritchard PH, Lacko AG. Structural differences between wild-type and fish eye disease mutant of lecithin:cholesterol acyltransferase. J Biomol Struct Dyn 2006; 24:75-82. [PMID: 16780378 DOI: 10.1080/07391102.2006.10507101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Fluorescence spectroscopy has been used to investigate the conformational changes that occur upon binding of wild type (WT) and mutant (Thr123Ile) lecithin:cholesterol acyltransferase (LCAT) to the potential substrates (dioleoyl-phosphatidyl choline [DOPC] and high density lipoprotein [HDL]). For a detailed analysis of structural differences between WT and mutant LCAT, we performed decompositional analysis of a set of tryptophan fluorescence spectra, measured at increasing concentrations of external quenchers (acrylamide and KI). The data obtained show that Thr123Ile mutation in LCAT leads to a conformation that is likely to be more rigid (less mobile/flexible) than that of the WT protein with a redistribution of charged residues around exposed tryptophan fluorophores. We propose that the redistribution of charged residues in mutant LCAT may be a major factor responsible for the dramatically reduced activity of the enzyme with HDL and reconstituted high density lipoprotein (rHDL).
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Affiliation(s)
- Yana Reshetnyak
- Department of Physics, University of Rhode Island, Kingston, Rhode Island 02881, USA.
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Hiraoka M, Abe A, Shayman JA. Structure and function of lysosomal phospholipase A2: identification of the catalytic triad and the role of cysteine residues. J Lipid Res 2005; 46:2441-7. [PMID: 16106046 DOI: 10.1194/jlr.m500248-jlr200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lysosomal phospholipase A2 (LPLA2) is an acidic phospholipase that is highly expressed in alveolar macrophages and that may play a role in the catabolism of pulmonary surfactant. The primary structure found in LCAT is conserved in LPLA2, including three amino acid residues potentially required for catalytic activity and four cysteine residues. LPLA2 activity was measured in COS-7 cells transfected with c-myc-conjugated mouse LPLA2 (mLPLA2) or mutated LPLA2. Single alanine substitutions in the catalytic triad resulted in the elimination of LPLA2 activity. Four cysteine residues (C65, C89, C330, and C371), conserved between LPLA2 and LCAT, were replaced with alanine. Quadruple mutations at C65, C89, C330, and C371, double mutations at C65 and C89, and a single mutation at C65 or C89 resulted in the elimination of activity. Double mutations at C330 and C371 and a single mutation at C330 or C371 resulted in a partial reduction of activity. Thus, the presence of a disulfide bond between C330 and C371 is not required for LPLA2 activity. We propose that one disulfide bond between C65 and C89 and free cysteine residues at C330 and C371 and the triad, serine-198, aspartic acid-360, and histidine-392, are required for the full expression of mLPLA2 activity.
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Affiliation(s)
- Miki Hiraoka
- Nephrology Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA
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12
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Lane SB, Tchedre KT, Nair MP, Thigpen AE, Lacko AG. Characterization of lecithin:cholesterol acyltransferase expressed in a human lung cell line. Protein Expr Purif 2005; 36:157-64. [PMID: 15249036 DOI: 10.1016/j.pep.2004.03.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2003] [Revised: 01/09/2004] [Indexed: 11/19/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme for the transfer of mammalian cholesterol from peripheral tissues to the liver. In patients deficient in LCAT, serum cholesterol levels rise and can lead to corneal opacity, proteinuria, anemia, and kidney failure. As early as 1968, relatively low volume transfusion of normal plasma was shown to temporarily correct the abnormal lipoprotein profiles in LCAT-deficient patients. However, despite the cloning, study, and extensive expression of LCAT in mammalian cell lines, there is still no viable, clinical therapy for LCAT deficiency. The current study was initiated to provide a source of recombinant human LCAT for enzyme replacement therapy. Accordingly, human LCAT has been cloned and expressed for the first time in a human cell line. The recombinant LCAT secreted by these cells was purified by phenyl-Sepharose chromatography, analyzed to determine the nature of its glycosylation, and tested for its enzymatic properties. The activity and basic kinetic parameters for the enzyme were determined using both a fluorescent water-soluble substrate and a macromolecular (proteoliposome) substrate. The enzymatic properties and the carbohydrate components of the recombinant LCAT were all sufficiently similar to those of the circulating human plasma enzyme, suggesting that this source of LCAT may be appropriate for use in some form of enzyme replacement therapy.
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Miida T, Zhang B, Obayashi K, Seino U, Zhu Y, Ito T, Nakamura Y, Okada M, Saku K. T13M mutation of lecithin-cholesterol acyltransferase gene causes fish-eye disease. Clin Chim Acta 2004; 343:201-8. [PMID: 15115696 DOI: 10.1016/j.cccn.2004.01.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2003] [Revised: 01/19/2004] [Accepted: 01/21/2004] [Indexed: 11/28/2022]
Abstract
BACKGROUND Lecithin-cholesterol acyltransferase (LCAT) esterifies free cholesterol (FC) in plasma and plays a crucial role in the maturation of prebeta1-HDL (lipid-poor HDL) into alpha-migrating HDL (spherical HDL). Natural mutations of LCAT gene cause familial LCAT deficiency (FLD) or fish-eye disease (FED). The relationship between mutations and their phenotypes gives important clues to the functions of specific regions of LCAT. We investigated the first homozygous case with a substitution of threonine to methionine at codon 13 (T13M) of LCAT gene. METHODS We evaluated LCAT activity, LCAT distribution among HDL subfractions and conversion of prebeta1-HDL to alpha-migrating HDL by native two-dimensional gel electrophoresis (N-2DGE). RESULTS The proband had corneal opacity, severe hypo-alpha-lipoproteinemia, half-normal LCAT activity and near normal cholesteryl ester/total cholesterol (TC) ratio in plasma. These features were characteristic of FED. Plasma prebeta1-HDL concentration was near normal, but not converted to alpha-migrating HDL during 37 degrees C incubation. As expected, alpha-migrating HDL (especially large particles) was markedly reduced. In the immunoblot against LCAT, the small alpha-migrating HDL from the proband had much less LCAT in this patient than in controls. CONCLUSION T13M mutation of LCAT gene causes FED.
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Affiliation(s)
- Takashi Miida
- Division of Clinical Preventive Medicine, Department of Community Preventive Medicine, Niigata University Graduate School of Medical and Dental Sciences, Asahimachi 1-757, Niigata, Niigata 951-8510, Japan.
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14
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Ståhl U, Carlsson AS, Lenman M, Dahlqvist A, Huang B, Banas W, Banas A, Stymne S. Cloning and functional characterization of a phospholipid:diacylglycerol acyltransferase from Arabidopsis. PLANT PHYSIOLOGY 2004; 135:1324-35. [PMID: 15247387 PMCID: PMC519051 DOI: 10.1104/pp.104.044354] [Citation(s) in RCA: 205] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2004] [Revised: 05/21/2004] [Accepted: 05/22/2004] [Indexed: 05/17/2023]
Abstract
A new pathway for triacylglycerol biosynthesis involving a phospholipid:diacylglycerol acyltransferase (PDAT) was recently described (Dahlqvist A, Stahl U, Lenman M, Banas A, Lee M, Sandager L, Ronne H, Stymne S, [2000] Proc Natl Acad Sci USA 97: 6487-6492). The LRO1 gene that encodes the PDAT was identified in yeast (Saccharomyces cerevisiae) and shown to have homology with animal lecithin:cholesterol acyltransferase. A search of the Arabidopsis genome database identified the protein encoded by the At5g13640 gene as the closest homolog to the yeast PDAT (28% amino acid identity). The cDNA of At5g13640 (AtPDAT gene) was overexpressed in Arabidopsis behind the cauliflower mosaic virus promoter. Microsomal preparations of roots and leaves from overexpressers had PDAT activities that correlated with expression levels of the gene, thus demonstrating that this gene encoded PDAT (AtPDAT). The AtPDAT utilized different phospholipids as acyl donor and accepted acyl groups ranging from C10 to C22. The rate of activity was highly dependent on acyl composition with highest activities for acyl groups containing several double bonds, epoxy, or hydroxy groups. The enzyme utilized both sn-positions of phosphatidylcholine but had a 3-fold preference for the sn-2 position. The fatty acid and lipid composition as well as the amounts of lipids per fresh weight in Arabidopsis plants overexpressing AtPDAT were not significantly different from the wild type. Microsomal preparations of roots from a T-DNA insertion mutant in the AtPDAT gene had barely detectable capacity to transfer acyl groups from phospholipids to added diacylglycerols. However, these microsomes were still able to carry out triacylglycerol synthesis by a diacylglycerol:diacylglycerol acyltransferase reaction at the same rate as microsomal preparations from wild type.
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Affiliation(s)
- Ulf Ståhl
- Department of Crop Science, Swedish University of Agricultural Sciences, S-230 53 Alnarp, Sweden
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15
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Abstract
In recent years, the impressive development of molecular genetics tools, the sequencing of the Arabidopsis thaliana genome, the availability of DNA or transposon tagged mutants, and the multiple possibilities offered by stable transformation with DNA in sense and antisense orientation have enabled the application of a strategy of gain or loss of function to study the sterol biosynthesis pathway. Here we describe the results obtained with these techniques. The results essentially confirm data obtained previously with sterol biosynthesis inhibitors (SBIs) and enable the precise dissection of biosynthetic pathways. We discuss the advantages and disadvantages of molecular genetics techniques as applied to sterol metabolism. The greater selectivity of these techniques constitutes an invaluable advantage and has led to the discovery of a role for sterols in plant development.
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Affiliation(s)
- Pierre Benveniste
- Institut de Biologie Moleculaire des Plantes, Departement Biogenese et Fonctions des Isoprenoides, UPR-CNRS 2357, 28 rue Goethe, 67083 Strasbourg, France.
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16
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Vickaryous NK, Teh EM, Stewart B, Dolphin PJ, Too CKL, McLeod RS. Deletion of N-terminal amino acids from human lecithin:cholesterol acyltransferase differentially affects enzyme activity toward alpha- and beta-substrate lipoproteins. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1646:164-72. [PMID: 12637024 DOI: 10.1016/s1570-9639(03)00005-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for generation of the majority of the cholesteryl esters (CE) in human plasma. Although most plasma cholesterol esterification occurs on high-density lipoprotein (HDL), via alpha-LCAT activity, esterification also occurs on low-density lipoprotein (LDL) via the beta-activity of the enzyme. Computer threading techniques have provided a three-dimensional model for use in the structure-function analysis of the core and catalytic site of the LCAT protein, but the model does not extend to the N-terminal region of the enzyme, which may mediate LCAT interaction with lipoprotein substrates. In the present study, we have examined the functional consequences of deletion of the highly conserved hydrophobic N-terminal amino acids (residues 1-5) of human LCAT. Western blot analysis showed that the mutant proteins (Delta 1-Delta 5) were synthesized and secreted from transfected COS-7 cells at levels approximately equivalent to those of wild-type hLCAT. The secreted proteins had apparent molecular weights of 67 kDa, indicating that they were correctly processed and glycosylated during cellular transit. However, deletion of the first residue of the mature LCAT protein (Delta 1 mutant) resulted in a dramatic loss of alpha-LCAT activity (5% of wild type using reconstituted HDL substrate, rHDL), although this mutant retained full beta-LCAT activity (108% of wild-type using human LDL substrate). Removal of residues 1 and 2 (Delta 2 mutant) abolished alpha-LCAT activity and reduced beta-LCAT activity to 12% of wild type. Nevertheless, LCAT Delta 1 and Delta 2 mutants retained their ability to bind to rHDL and LDL lipoprotein substrates. The dramatic loss of enzyme activity suggests that the N-terminal residues of LCAT may be involved in maintaining the conformation of the lid domain and influence activation by the alpha-LCAT cofactor apoA-I (in Delta 1) and/or loss of enzyme activity (in Delta 1-Delta 5). Since the Delta 1 and Delta 2 mutants retain their ability to bind substrate, other factor(s), such as decreased access to the substrate binding pocket, may be responsible for the loss of enzyme activity.
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Affiliation(s)
- Nicola K Vickaryous
- Department of Biochemistry and Molecular Biology, Dalhousie University, Room 9F, Sir Charles Tupper Medical Building, Halifax, Nova Scotia, Canada B3H 1X5
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17
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Wang K, Subbaiah PV. Role of the interfacial binding domain in the oxidative susceptibility of lecithin:cholesterol acyltransferase. Biochem J 2002; 365:649-57. [PMID: 11966470 PMCID: PMC1222714 DOI: 10.1042/bj20020064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2002] [Revised: 04/16/2002] [Accepted: 04/19/2002] [Indexed: 11/17/2022]
Abstract
We had previously shown that the cholesterol esterification activity of lecithin:cholesterol acyltransferase (LCAT) is destroyed by oxidation, but still it retains the ability to hydrolyse water-soluble substrates. This suggested that the inactivation of the enzyme is not due to its catalytic function, but due to a loss of its hydrophobic binding. Since recent studies have shown that a tryptophan residue in the putative interfacial domain (Trp(61)) is critical for the activity, we determined the possible role of this residue in the oxidative susceptibility and substrate specificity of LCAT by site-directed mutagenesis. Deletion of Trp(61) resulted in a 56% loss of cholesterol esterification (LCAT) activity, but the phospholipase A(2) (PLA(2)) and the esterase activities of the enzyme were stimulated slightly. Replacing Trp(61) with another aromatic residue [Trp(61)-->Tyr (W61Y)] resulted in an increase in all activities (14-157%), whereas replacing it with an aliphatic residue [Trp(61)-->Gly (W61G)] caused a dramatic loss of LCAT (-90%) and PLA(2) (-82%) activities, but not the esterase activity (-5%). W61Y was the most sensitive to oxidation, whereas W61G was the most resistant, with respect to the LCAT and PLA(2) activities. However, the activities which do not involve interfacial binding, namely the esterase activity and the transesterification of short-chain phospholipids, were more resistant to oxidation in all LCATs, indicating a selective loss of the interfacial binding by oxidation. Furthermore, replacing the two cysteines (Cys(31) and Cys(184)) in the Trp(61) deletion mutant caused additional resistance of the enzyme to oxidizing agents, showing that both domains of the enzyme contribute independently to its oxidative susceptibility. Since the hydrolysis of truncated phospholipids, generated during the oxidation of low-density lipoproteins, does not require the interfacial-binding domain, our results suggest that LCAT may take part in the detoxification of these compounds even after the loss of its cholesterol esterification function.
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Affiliation(s)
- Kewei Wang
- Department of Medicine, Rush Medical College, 1653 West Congress Parkway, Chicago, IL 60612-3833, U.S.A
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18
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Affiliation(s)
- Pierre Benveniste
- Institut de Biologie Moleculaire des Plantes, Departement Biogénèse et Fonctions des Isoprénoides, UPR-CNRS 2357, 28 rue Goethe, 67083-Strasbourg, France
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19
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Kosman J, Jonas A. Deletion of specific glycan chains affects differentially the stability, local structures, and activity of lecithin-cholesterol acyltransferase. J Biol Chem 2001; 276:37230-6. [PMID: 11486003 DOI: 10.1074/jbc.m104326200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The enzymatic and interfacial binding activity of lecithin-cholesterol acyltransferase (LCAT) is affected differentially by the location and extent of its glycosylation. Two LCAT glycosylation-deficient mutants, N84Q and N384Q, were constructed, permanently expressed in Chinese hamster ovary cells, and purified to determine the effects of deleting individual glycan chains on its stability, structure, and function. These purified mutants were studied by spectroscopic structural methods and enzymatic and binding assays to develop a molecular rationale for the relationship between LCAT glycosylation and activity. The N84Q LCAT mutant did not possess measurable enzymatic activity or interfacial binding affinity for reconstituted high-density lipoproteins. In addition, in thermal and chemical denaturation studies, N84Q LCAT was found to be significantly less stable than wild-type LCAT. The N384Q variant was initially more enzymatically active than wild-type LCAT, but gradually lost activity within months; however, it retained full interfacial binding activity. Significant changes were detected over time by circular dichroism in the alpha-helical content of N384Q LCAT and in the beta-sheet content of N84Q LCAT, compared with wild-type LCAT. Fluorescence measurements with the probe 1-anilinonapthalene-8-sulfonate suggested an alteration of the active site cavity in both mutants. In conclusion, both mutants lost catalytic activity, N84Q shortly after purification and N384Q more gradually, and were destabilized, probably because the deletion of the glycan chains altered local structural elements near the active site cavity and/or the interfacial binding regions.
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Affiliation(s)
- J Kosman
- Department of Biochemistry, College of Medicine at Urbana-Champaign, University of Illinois, Urbana, Illinois 61801, USA
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20
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Murray KR, Nair MP, Ayyobi AF, Hill JS, Pritchard PH, Lacko AG. Probing the 121-136 domain of lecithin:cholesterol acyltransferase using antibodies. Arch Biochem Biophys 2001; 385:267-75. [PMID: 11368007 DOI: 10.1006/abbi.2000.2154] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) catalyzes the esterification of plasma lipoprotein cholesterol in mammals as part of the reverse cholesterol transport pathway. Studies of the natural mutations of LCAT revealed a region that is highly sensitive to mutations (residues 121-136) and it is highly conserved in six animal species. The purpose of these studies was to investigate the reactivity of wild type and several mutated forms of LCAT, with a series polyclonal antibodies to further characterize this specific domain (residues 121-136). Two polyclonal antibodies directed against the whole enzyme, one against human plasma LCAT and the other against purified recombinant LCAT, and one site specific polyclonal antibody, directed against the 121-136 region of LCAT, were employed. All three antibodies reacted with a recombinant form of purified LCAT; however, only the polyclonal antibodies directed against the whole enzyme were able to recognize the LCAT when it was adsorbed to a hydrophobic surface in a solid phase immunoassay, or when bound to HDL in a sink immunoassay. These findings indicate that the epitope(s) of the 121-136 region are not accessible to antibodies under these conditions. Three mutant forms of LCAT, representing alterations in the 121-136 region, were also examined for their immunoreactivity with the same panel of antibodies and compared to the wild-type enzyme. These studies demonstrate that in its native configuration the 121-136 region of LCAT is likely to reside on a surface of LCAT. Furthermore, mutations within this region appear to markedly impact the exposure of epitopes at additional sites. These findings suggest that the 121-136 region could play an important role in enzyme interaction with its hydrophobic lipoprotein substrates as mutations within this region appear to alter enzyme conformation, catalytic activity, and the specificity of LCAT.
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Affiliation(s)
- K R Murray
- Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, USA
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22
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Segrest JP, Harvey SC, Zannis V. Detailed molecular model of apolipoprotein A-I on the surface of high-density lipoproteins and its functional implications. Trends Cardiovasc Med 2000; 10:246-52. [PMID: 11282302 DOI: 10.1016/s1050-1738(00)00078-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The major apolipoprotein (apo) A-I containing lipoprotein, high- density lipoprotein, is a negative risk factor for cardiovascular disease. An atomic resolution molecular model for lipid-associated apo A-I was recently proposed in which two apo A-I molecules are wrapped beltwise around a small discoidal patch of phospholipid bilayer. Because of its detailed predictions of lipid-associated apo A-I structure, this molecular belt model, if confirmed, provides a blueprint for understanding the molecular mechanisms of reverse cholesterol transport, and thus for the rational design of new classes of drugs for reversal of atherosclerosis and cardiovascular disease. The details and implications of the model are currently being explored by site-directed mutagenesis.
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Affiliation(s)
- J P Segrest
- Department of Medicine at the UAB Medical Center, Birmingham, Alabama 35149-0012, USA.
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23
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Christiaens B, Vanloo B, Gouyette C, Van Vynckt I, Caster H, Taveirne J, Verhee A, Labeur C, Peelman F, Vandekerckhove J, Tavernier J, Rosseneu M. Headgroup specificity of lecithin cholesterol acyltransferase for monomeric and vesicular phospholipids. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1486:321-7. [PMID: 10903483 DOI: 10.1016/s1388-1981(00)00075-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
In this study, we investigated how the nature of the phospholipid head group and the macromolecular structure of the phospholipid, either as a monomer or incorporated into a lipid matrix, influence the activity of lecithin cholesterol acyltransferase (LCAT). As substrates we used 1,2-bis-(1-pyrenebutanoyl)-phosphatidylcholine, 1, 2-bis-(1-pyrenebutanoyl)-phosphatidylethanolamine and 1, 2-bis-(1-pyrenebutanoyl)-phosphatidyl-alcohols, either as monomers or incorporated into small unilamellar vesicles consisting of dipalmitoylphosphatidylcholine ether. The rate of hydrolysis of the pyrene-labeled phospholipids was determined both by fluorescence and by high performance liquid chromatography. V(max) and K(m) were calculated for the different substrates. The data show that V(max) is 10- to 30-fold higher for the hydrolysis of monomeric phosphatidylcholine (PC) compared to phosphatidylethanolamine (PE) and the phosphatidylalcohols, while K(m) values are comparable. When the fluorescent substrates were incorporated into dipalmitoylphosphatidylcholine ether vesicles, we observed a 4- to 10-fold increase of V(max) for PE and the phosphatidylalcohols, and no significant change for K(m). V(max) for PC remained the same. Natural LCAT mutants causing Fish-Eye Disease (FED) and analogues of these mutants expressed in Cos-1 cells, had similar activity on monomeric PC and PE. These data suggest that the activity of LCAT is determined both by the molecular structure of the phospholipid and by its macromolecular properties. The LCAT activity on monomeric substrates decreases as: phosphatidylcholine&z. Gt;phosphatidylethanolamine congruent withphosphatidylpropanol congruent withphosphatidylethanol congruent withphosphatidylethyleneglycol. The incorporation of PE and the phosphatidylalcohols into a matrix of dipalmitoylphosphatidylcholine decreases the specificity of the phospholipid head group.
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Affiliation(s)
- B Christiaens
- Department of Biochemistry, Ghent University, Belgium
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24
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Vanloo B, Peelman F, Deschuymere K, Taveirne J, Verhee A, Gouyette C, Labeur C, Vandekerckhove J, Tavernier J, Rosseneu M. Relationship between structure and biochemical phenotype of lecithin:cholesterol acyltransferase (LCAT) mutants causing fish-eye disease. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32384-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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25
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Peelman F, Vandekerckhove J, Rosseneu M. Structure and function of lecithin cholesterol acyl transferase: new insights from structural predictions and animal models. Curr Opin Lipidol 2000; 11:155-60. [PMID: 10787177 DOI: 10.1097/00041433-200004000-00008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The enzyme lecithin cholesterol acyl transferase is responsible for the synthesis of most of the cholesteryl esters in plasma, and therefore plays a key role in lipoprotein metabolism. The relationship between the structure and function of lecithin cholesterol acyl transferase has been extensively studied in the past years, and new data appeared in 1999 documenting the substrate specificity and physiological role of lecithin cholesterol acyl transferase. The discovery of natural mutants, together with the proposal of a three-dimensional model for the enzyme, has provided new tools to unravel the function of specific residues of lecithin cholesterol acyl transferase. The use of transgenic animals and the production of knock-out lecithin cholesterol acyl transferase mice has further contributed to the understanding of the lecithin cholesterol acyl transferase 'in vivo' function. Evidence for a protective role of lecithin cholesterol acyl transferase against the development of atherosclerosis through the hydrolysis of oxidized lipids was recently proposed. Lecithin cholesterol acyl transferase patterns in several pathologies were further clarified. These newer developments are reviewed here.
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Affiliation(s)
- F Peelman
- Department of Biochemistry, Faculty of Medicine, Universiteit Gent, Belgium
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Jin L, Shieh JJ, Grabbe E, Adimoolam S, Durbin D, Jonas A. Surface plasmon resonance biosensor studies of human wild-type and mutant lecithin cholesterol acyltransferase interactions with lipoproteins. Biochemistry 1999; 38:15659-65. [PMID: 10569952 DOI: 10.1021/bi9916729] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Binding of lecithin cholesterol acyltransferase (LCAT) to lipoprotein surfaces is a key step in the reverse cholesterol transport process, as the subsequent cholesterol esterification reaction drives the removal of cholesterol from tissues into plasma. In this study, the surface plasmon resonance method was used to investigate the binding kinetics and affinity of LCAT for lipoproteins. Reconstituted high-density lipoproteins (rHDL) containing apolipoprotein A-I or A-II, (apoA-I or apoA-II), low-density lipoproteins (LDL), and small unilamellar phosphatidylcholine vesicles, with biotin tags, were immobilized on biosensor chips containing streptavidin, and the binding kinetics of pure recombinant LCAT were examined as a function of LCAT concentration. In addition, three mutants of LCAT (T123I, N228K, and (Delta53-71) were examined in their interactions with LDL. For the wild-type LCAT, binding to all lipid surfaces had the same association rate constant, k(a), but different dissociation rate constants, k(d), that depended on the presence of apoA-I (k(d) decreased) and different lipids in LDL. Furthermore, increased ionic strength of the buffer decreased k(a) for the binding of LCAT to apoA-I rHDL. For the LCAT mutants, the Delta53-71 (lid-deletion mutant) exhibited no binding to LDL, while the LCAT-deficiency mutants (T123I and N228K) had nearly normal binding to LDL. In conclusion, the association of LCAT to lipoprotein surfaces is essentially independent of their composition but has a small electrostatic contribution, while dissociation of LCAT from lipoproteins is decreased due to the presence of apoA-I, suggesting protein-protein interactions. Also, the region of LCAT between residues 53 and 71 is essential for interfacial binding.
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Affiliation(s)
- L Jin
- Department of Biochemistry, University of Illinois at Urbana-Champaign 61801, USA
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