Advances in lipid research. . V. 21

492 Pages·1985·84.472 MB·English

by  Rodolfo Paoletti, David Kritchevsky

EDITORIAL ADVISORY BOARD
B. LEWIS G. SCHLIERF
A. V. NICHOLS C. SIRTORI
G. H. ROTHBLAT R. W. WlSSLER
CONTRIBUTORS
PIERRE BORGEAT PATRICE POUBELLE
PETER M. BRAMLEY RAJENDRA PRASAD
ABOL-HASSAN ETEMADI HASSAN SALARI
BERNARD FRUTEAU DE LACLOS PIERRE SIROIS
PATRICIA V. JOHNSTON CHARLES E. SPARKS
MARIE NADEAU JANET D. SPARKS
PATRICK TSO
EDITORIAL ADVISORY BOARD
B. LEWIS G. SCHLIERF
A. V. NICHOLS C. SIRTORI
G. H. ROTHBLAT R. W. WlSSLER
CONTRIBUTORS
PIERRE BORGEAT PATRICE POUBELLE
PETER M. BRAMLEY RAJENDRA PRASAD
ABOL-HASSAN ETEMADI HASSAN SALARI
BERNARD FRUTEAU DE LACLOS PIERRE SIROIS
PATRICIA V. JOHNSTON CHARLES E. SPARKS
MARIE NADEAU JANET D. SPARKS
PATRICK TSO
Advances
in
Lipid
Research
Volume 21
Edited by
Rodolfo Paoletti
Institute of Pharmacology
University of Milan
Milan, Italy
David Kritchevsky
The Wistar Institute
Philadelphia, Pennsylvania
1985
ACADEMIC PRESS, INC.
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COPYRIGHT © 1985, BY ACADEMIC PRESS, INC.
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CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors' contributions
begin.
PIERRE BORGEAT, Groupe de Recherche sur les Leucotriènes,
Laboratoire d'Endocrinologie Moléculaire, Le Centre Hospita-
lier de V Université Laval, Québec G1V 4G2, Canada (47)
PETER M. BRAMLEY, Department of Biochemistry, Royal Hollo-
way College, University of London, Egham, Surrey TW20 OEX,
England (243)
ABOL-HASSAN ETEMADI, Laboratoire de Biochimie et de Biologie
Moléculaire des Lipides Bactériens, Faculté des Sciences de
l'Université Paris VI, 75005 Paris, France (281)
BERNARD FRUTEAU DE LACLOS, Groupe de Recherche sur les
Leucotriènes, Laboratoire d'Endocrinologie Moléculaire, Le
Centre Hospitalier de Γ Université Laval, Québec G1V 4G2,
Canada (47)
PATRICIA V. JOHNSTON, Department of Food Science and Divi-
sion of Nutritional Sciences, University of Illinois at Urbana-
Champaign, Urbana, Illinois 61801 (103)
MARIE NADEAU, Groupe de Recherche sur les Leucotriènes, La-
boratoire d'Endocrinologie Moléculaire, Le Centre Hospitalier
de l'Université Laval, Québec G1V 4G2, Canada (47)
PATRICE POUBELLE, Groupe de Recherche sur les Leucotriènes,
Laboratoire d'Endocrinologie Moléculaire, Le Centre Hospita-
lier de l'Université Laval, Québec G1V 4G2, Canada (47)
RAJENDRA PRASAD, School of Life Sciences, Jawaharlal Nehru
University, New Delhi 110 067, India (187)
HASSAN SALARI, Groupe de Recherche sur les Leucotriènes, La-
boratoire d'Endocrinologie Moléculaire, Le Centre Hospitalier
de l'Université Laval, Québec G1V 4G2, Canada (47)
IX
X CONTRIBUTORS
PIERRE SIROIS, Départements de Pédiatrie et de Pharmacologie,
Faculté de Médecine, Université de Sherbrooke, Sherbrooke,
Québec J1H 5N4, Canada (79)
CHARLES E. SPARKS, Department of Pathology and Laboratory
Medicine, University of Rochester School of Medicine and Den-
tistry, Rochester, New York, 14642 (1)
JANET D. SPARKS, Department of Pathology and Laboratory Med-
icine, University of Rochester School of Medicine and Dentistry,
Rochester, New York, 14642 (1)
PATRICK TSO, Department of Physiology and Biophysics, The Uni-
versity of Tennessee, Memphis, Tennessee 38163 (143)
PREFACE
Volume 21 of Advances in Lipid Research touches on several important
and emerging areas in lipid metabolism, including apolipoprotein metabo-
lism, leukotrienes, and the role of fat in the functioning of the immune
system.
Research on lipoprotein metabolism and hyperlipidemias has pro-
gressed from investigation of serum or plasma proteins to the protein
components of the lipoprotein molecule. Apolipoprotein B is the principal
protein of chylomicrons, very low density and low density lipoproteins,
and the first chapter in this volume relates to its metabolism.
Among the products obtained in the course of the metabolism of arachi-
donic acid are prostaglandins, thromboxanes, and leukotrienes. The last
of these is the subject of the second and third articles in this volume.
These chapters describe the biosynthesis, metabolism, and pharmacology
of leukotrienes. Reflecting the current interest in the eicosanoids, the next
chapter discusses the role of essential fatty acids in the immune system.
The relation of lipids to immunology is a relatively recent observation and
is dealt with in this chapter.
It has been several years since digestion and absorption of lipid have
been discussed in this series. This oversight is corrected in the thorough
treatment of this area in the fifth chapter. The sixth article deals with the
role(s) played by lipids in the structure and function of the yeast mem-
brane. The influence of lipids on structure and function of mammalian
membranes has been the subject of intensive research in the past decade.
The sixth chapter reminds us of how much we can learn from the study of
membranes of other biological systems.
The general importance in the plant kingdom and the place of some
carotenoids in human biology makes the seventh chapter on in vitro bio-
synthesis of carotenoids particularly pertinent at this time.
The final article presents an exhaustive review of the influence of pro-
teins on configuration and function of reconstituted lipid membranes.
RODOLFO PAOLETTI
DAVID KRITCHEVSKY
xi
ADVANCES IN LIPID RESEARCH, VOL. 21
Apolipoprotein B and Lipoprotein Metabolism
JANET D. SPARKS AND CHARLES E. SPARKS
Department of Pathology and Laboratory Medicine
University of Rochester School of Medicine and Dentistry
Rochester, New York
I. Introduction 1
II. Characterization of ApoB 2
A. Biochemical Properties of ApoB 2
B. Molecular Weight of ApoB of Low-Density Lipoproteins 4
C. ApoB Variants 8
D. Immunochemistry of ApoB 11
III. Metabolism of ApoB in Lipoproteins 16
A. Lipoprotein Receptors 16
B. Chylomicron ApoB 18
C. Very Low-Density Lipoprotein ApoB 25
D. Low-Density Lipoprotein ApoB 35
E. High-Density Lipoprotein ApoB 37
IV. Conclusions 38
References 39
I. Introduction
Apolipoprotein B (apoB) is an obligatory structural component of chy-
lomicrons (CM), very low-density lipoproteins (VLDL), low-density lipo-
proteins (LDL), and lipoproteins of intermediate density between VLDL
and LDL (IDL). ApoB is an organizational protein, and much like mem-
brane proteins, its peculiar chemical and physical properties reflect its
role in mediating a lipid environment with an aqueous environment. ApoB
proteins become insoluble after removal of lipid and are precipitated by
4.2 M tetramethylurea (Kane, 1973). Because apoB does not undergo
soluble exchange reactions, the protein marks the lipoprotein particle
from the time it is synthesized until it is degraded. ApoB also acts as a
ligand in cellular recognition of lipoproteins by receptors. The association
of apoB as a positive risk factor in development of atherosclerosis and its
presence in the arterial wall in atherosclerotic lesions has drawn a great
deal of attention to this protein. In spite of this, a complete knowledge of
apoB structure and function is only slowly evolving.
1
Copyright © 1985 by Academic Press, Inc.
AH rights of reproduction in any form reserved.
ISBN 0-12-024921-9
2 JANET D. SPARKS AND CHARLES E. SPARKS
ApoB represents 10-20% of CM protein, 40% of VLDL protein, and
95-98% of LDL protein. There are about 0.1-0.6 mg of apoB/100 mg of
CM, l-5mg/100mgofVLDL,and 17-32 mg/100 mg of LDL. ApoB mass
per lipoprotein particle ranges from 400,000 to 650,000 and remains
roughly the same over wide ranges of VLDL and LDL sizes (Eisenberg
and Levy, 1975). The apoB mass per CM particle is similar to that for
VLDL and LDL and is the same for variously sized CM (Bhattacharya
and Redgrave, 1981). Formation and secretion of CM by the intestine and
VLDL by the liver requires apoB (Eisenberg and Levy, 1975). The recent
finding in humans of a lower molecular weight variant of apoB synthe-
sized by the intestine (apoB ) and a higher molecular weight variant of
L
apoB synthesized by the liver (apoB ) has stimulated a réévaluation of
H
apoB metabolic pathways.
The present article will include a discussion of recent developments in
the characterization of the structure of apoB, both biochemically and
immunochemically, and how its newly discovered variant heterogeneity
relates to its reported metabolic heterogeneity. The immunochemistry of
apoB, and in particular, recent developments through the use of mono-
clonal antibody reagents, have been emphasized. It is not the intent of this
article to provide an exhaustive and comprehensive treatise on apoB
metabolism. We will attempt to focus on newly developing ideas on the
relationship of apoB to lipoprotein metabolism. For more extensive treat-
ments of lipoprotein composition, structure, and function and apoprotein
metabolism, the reader is referred to the following articles (Eisenberg and
Levy, 1975; Eisenberg, 1976, 1979, 1983; Jackson et al., 1976; Kane,
1977; Morrisett et al., 1977; Osborne and Brewer, 1977; Schaefer et al.,
1978a; Smith et al, 1978; Havel, 1980; Scanu and Landsberger, 1980;
Brewer, 1981).
II. Characterization of ApoB
A. BIOCHEMICAL PROPERTIES OF APOB
The ability to characterize fully the physicochemical nature of the
structure of apoB has been hampered by its insolubility (Cardin et al.,
1982), its susceptibility to degradation (Krishnaiah and Wiegandt, 1974)
and to oxidative cleavage (Schuh et al., 1978; Lee et al., 1981), and its
propensity to aggregate. Recently, water-soluble apoB has been prepared
(Jackson and Cardin, 1983) and the physical and chemical properties have
been described (Cardin et al., 1982). A study of similarly prepared apoB
may aid in determining the exact size and monomer molecular weight of
Apolipoprotein B 3
apoB. The primary structure of apoB of LDL is slowly being worked out
by analyzing products from cyanogen bromide cleavage (Bradley et al.,
1978) and from enzymatic digestions (Bradley et al., 1980; LeBoeuf et al.,
1984). This process is a slow one, as some cleavage peptides retain the
insolubility characteristics of the parent molecule.
Trypsin treatment of human LDL, however, renders the delipidated
apoB soluble in solutions containing detergents, and, unlike delipidated
apoB of native LDL, trypsin-treated apoB becomes soluble in aqueous
solutions at low concentrations and in 8 M urea at high concentrations
(Chapman et al., 1978). These results suggest that the trypsin-susceptible
portion contributes to the insolubility characteristics of native apoB. Ap-
proximately 20% of apoB is specifically removed by trypsin, and liberated
peptides are enriched in basic amino acids (arginine and lysine) and de-
pleted in acidic ones (aspartic acid and glutamic acid). Trypsin treatment
also removes 30-50% of the surface protein-bound carbohydrate, sug-
gesting that carbohydrate may also contribute to the insolubility charac-
teristics of apoB. The use of more soluble apoB-derived peptides from
specific cleavages of apoB will aid in delineating the amino acid sequences
required for LDL receptor interaction (Chapman et al., 1984).
The amino acid composition of apoB is similar to other apolipoproteins
(Schaefer et al., 1978a). The amino terminal residue is glutamic acid,
while the carboxyl terminal residue has been reported to be serine (Shore,
1957) and to be blocked (Eisenberg and Levy, 1975). In a recent report,
Cardin et al. (1982) found that apoB of LDL contained a total of 14
molecules of half-cystine per 250,000 g of protein; 2 were free while the
other 12 formed 6 pairs of intramolecular disulfide bonds. These investiga-
tors also demonstrated that by blocking free sulfhydryl residues in LDL
before lipid extraction the formation of large covalent aggregates by inter-
molecular cross-linking was inhibited. Their results support the mecha-
nism of cross-linking to be sulfhydryl-disulfide exchange catalyzed by the
two free sulfhydryls present in native apoB. The result of exchange reac-
tions is the replacement of intramolecular disulfide bonds with intermo-
lecular ones leading to irreversible aggregation. Recently, LeBoeuf et al.
(1984) used Staphylococcus aureus protease to produce large peptides
which were isolated in sufficient quantities to be subjected to amino acid
sequencing. The sequences of human apoB were unlike those reported for
other apolipoproteins. Several peptides were suitable for construction of
oligonucleotide probes. These types of reagents will undoubtedly lead to
determination of the absolute size and sequence of apoB through molecu-
lar cloning techniques.
ApoB of LDL is a glycoprotein. Carbohydrate represents about 5% of
the total apoB mass (Eisenberg and Levy, 1975), although carbohydrate