title: Lipoproteomics I: mapping of proteins in low-density lipoprotein using two-dimensional gel electrophoresis and mass spectrometry.
abstract: The molecular mechanisms underlying the relationship between low-density lipoprotein (LDL) and the risk of atherosclerosis are not clear. Therefore, detailed information about the protein composition of LDL may contribute to reveal its role in atherogenesis and the mechanisms that lead to coronary disease in humans. Here, we sought to map the proteins in human LDL by a proteomic approach. LDL was isolated by two-step discontinuous density-gradient ultracentrifugation and the proteins were separated with two-dimensional gel electrophoresis and identified with peptide mass fingerprinting, using matrix assisted laser desorption/ionization-time of flight-mass spectrometry and with amino acid sequencing using electrospray ionization tandem mass spectrometry. These procedures identified apo B-100, apo C-II, apo C-III (three isoforms), apo E (four isoforms), apo A-I (two isoforms), apo A-IV, apo J and apo M (three isoforms not previously described). In addition, three proteins that have not previously been identified in LDL were found: serum amyloid A-IV (two isoforms), calgranulin A, and lysozyme C. The identities of apo M, calgranulin A, and lysozyme C were confirmed by sequence information obtained after collision-induced dissociation fragmentation of peptides characteristic for these proteins. Moreover, the presence of lysozyme C was further corroborated by demonstrating enriched hydrolytic activity in LDL against Micrococcus lysodeikticus. These results indicate that in addition to the dominating apo B-100, LDL contains a number of other apolipoproteins, many of which occur in different isoforms. The demonstration, for the first time, that LDL contains calgranulin A and lysozyme C raises the possibility that LDL proteins may play hitherto unknown role(s) in immune and inflammatory reactions of the arterial wall.
authors.affiliation: Division of Occupational and Environmental Medicine, Department of Molecular and Clinical Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Helen
authors.initials: H
authors.lastname: Karlsson
authors.forename: Per
authors.initials: P
authors.lastname: Leanderson
authors.forename: Christer
authors.initials: C
authors.lastname: Tagesson
authors.forename: Mats
authors.initials: M
authors.lastname: Lindahl
mesh_terms: D016632:Apolipoprotein A-I / Q000032:analysis; D053299:Apolipoprotein B-100; D053305:Apolipoprotein C-III; D001053:Apolipoproteins / Q000032:analysis; D001054:Apolipoproteins A / Q000032:analysis; D001055:Apolipoproteins B / Q000032:analysis; D001056:Apolipoproteins C / Q000032:analysis; D001057:Apolipoproteins E / Q000032:analysis; D000075243:Apolipoproteins M; D040501:Calgranulin A / Q000032:analysis; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D051152:Clusterin; D015180:Electrophoresis, Gel, Two-Dimensional; D006023:Glycoproteins / Q000032:analysis; D006801:Humans; D054834:Lipocalins; D008077:Lipoproteins, LDL / Q000032:analysis* / Q000302:isolation & purification; D013058:Mass Spectrometry; D018832:Molecular Chaperones / Q000032:analysis; D010449:Peptide Mapping; D020033:Protein Isoforms / Q000032:analysis; D020543:Proteome / Q000032:analysis*; D040901:Proteomics; D020539:Sequence Analysis, Protein; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: C400523:APOM protein, human; D016632:Apolipoprotein A-I; D053299:Apolipoprotein B-100; D053305:Apolipoprotein C-III; D001053:Apolipoproteins; D001054:Apolipoproteins A; D001055:Apolipoproteins B; D001056:Apolipoproteins C; D001057:Apolipoproteins E; D000075243:Apolipoproteins M; C495242:CLU protein, human; D040501:Calgranulin A; D051152:Clusterin; D006023:Glycoproteins; D054834:Lipocalins; D008077:Lipoproteins, LDL; D018832:Molecular Chaperones; D020033:Protein Isoforms; D020543:Proteome; C022205:apolipoprotein A-IV