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Characterization of apolipoprotein M isoforms in low-density lipoprotein
Linköping University, Department of Clinical and Experimental Medicine, Occupational and Environmental Medicine . Linköping University, Faculty of Health Sciences.
Department of Chemistry and Bioscience/Food Science, Chalmers University of Technology, Göteborg, Sweden.
Linköping University, Department of Clinical and Experimental Medicine, Occupational and Environmental Medicine . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Occupational and Environmental Medicine . Linköping University, Faculty of Health Sciences.
2006 (English)In: Journal of proteome research, ISSN 1535-3893, Vol. 5, no 10, 2685-2690 p.Article in journal (Refereed) Published
Abstract [en]

Apo M is a recently discovered human lipoprotein thought to be involved in the metabolism of lipids and lipoprotein particles. Here, a proteomic approach was applied to examine the glycosylation pattern of apo M in human LDL. We treated LDL proteins with N-glycosidase or neuraminidase, studied mobility shifts of Apo M by two-dimensional gel electrophoresis, and different isoforms were then identified with mass spectrometry. This way, we demonstrated the presence of five isoforms of apo M in LDL:  three that are both N-glycosylated and sialylated, one that is N-glycosylated but not sialylated, and one that is neither N-glycosylated nor sialylated. As judged from the examination of LDL from 20 healthy human subjects, the three N-glycosylated and sialylated forms are most abundant (80−100% of the total apo M in LDL) whereas the unsialylated and unglycosylated variants constitute at most 20%. Comparative analysis showed that the same five isoforms of apo M are also present in HDL. Further studies aiming at elucidating the role of apo M in health and disease will have to take this polymorphism of apo M proteins into account.

Place, publisher, year, edition, pages
2006. Vol. 5, no 10, 2685-2690 p.
Keyword [en]
apolipoprotein M, apo M, low-density lipoprotein, LDL, two-dimensional gel electrophoresis, 2-DE, MALDI-TOF mass spectrometry, glycosylations, sialylations
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14353DOI: 10.1021/pr060180xOAI: oai:DiVA.org:liu-14353DiVA: diva2:23301
Available from: 2007-03-15 Created: 2007-03-15
In thesis
1. Lipoproteomics: A New Approach to the Identification and Characterization of Proteins in LDL and HDL
Open this publication in new window or tab >>Lipoproteomics: A New Approach to the Identification and Characterization of Proteins in LDL and HDL
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A proteomic approach was applied to examine the protein composition of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in humans. LDL and HDL were isolated by density gradient ultracentrifugation, and proteins were separated with twodimensional gel electrophoresis (2-DE) 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. To improve the identification of low abundant proteins in silver stained 2-DE gels, 2,5-dihydroxybenzoic acid was used instead of α-cyano-4-hydroxycinnamic acid as matrix in the peptide mass fingerprinting procedure; this was demonstrated to give more matching peptide peaks, higher sequence coverage, and higher signal to noise ratio. Altogether 18 different proteins were demonstrated in LDL and/or HDL: three of these (calgranulin A, lysozyme C and transthyretin) have not been identified in LDL before. Apo C-II, apo C-III, apo E, apo A-I, apo A-IV, apo J, apo M, serum amyloid A-IV and α1-antitrypsin were found in both LDL and HDL, while apo B-100 (clone), calgranulin A, lysozyme C and transthyretin were found only in LDL, and apo A-II, apo C-I, and serum amyloid A only in HDL. Salivary α-amylase wass identified only in HDL2, and apo L and glycosylated apo A-II only in HDL3. Many of the proteins occurred in a number of isoforms: in all, 47 different isoform identities were demonstrated. A 2-DE mobility shift assay and deglycosylation experiments were used to demonstrate, for the first time, that apo M in LDL and HDL occurs in five isoforms; three that are both N-glycosylated and sialylated, one that is N-glycosylated but not sialylated and one that is neither N-glycosylated nor sialylated. LDL from obese subjects was found to contain more apo J, apo C-II, apo M, α1-antitrypsin and serum amyloid A-IV than LDL from controls,, and also more of an acidic isoform (pI/Mr; 5.2 / 23 100) of apo A-I. In addition, the new LDLassociated protein transthyretin, was found to be significantly more abundant in LDL from obese subjects. On the other hand, the amounts of apo A-IV and the major isoform of apo A-I (pI/Mr; 5.3 / 23 100) were significantly less. Altogether, these findings (i) illustrate the power of 2-DE and mass spectrometry for detailed mapping of the proteins and their isoforms in human lipoproteins; (ii) demonstrate the presence of a number of new proteins in LDL (calgranulin A, lysozyme C and transthyretin); (iii) give precise biochemical clues to the polymorphism of apo M in LDL and HDL, and; (iv) indicate that obesity is associated with significant changes in the protein profile of LDL. It is concluded that new information on lipoproteins can easily be obtained through a proteomic approach, thus facilitating the development of a new proteomic field: lipoproteomics. Much further investigation in this field is warranted, particularly because newly discovered LDL and HDL proteins may play hitherto unknown role(s) in inflammatory reactions of the arterial wall and evolve as useful biomarkers in cardiovascular disease.

Place, publisher, year, edition, pages
Institutionen för molekylär och klinisk medicin, 2007
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 986
Keyword
LDL, HDL, Proteomik, Atheroskleros, Masspektrometri, 2-DE
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-8527 (URN)978-91-85715-47-3 (ISBN)
Public defence
2007-03-29, Aulan, Hälsans Hus, Campus US, Linköpings Universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-08-22

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Karlsson, HelenTagesson, ChristerLindahl, Mats

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