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Alpha1-microglobulin chromophores are located to three lysine residues semiburied in the lipocalin pocket and associated with a novel lipophilic compound

Berggård, T LU ; Lindqvist, A LU ; Cedervall, T LU ; Akerström, B LU ; Thøgersen, I B ; Enghild, J J ; Cohen, A LU ; Persson, P ; Jönsson, J A LU and Silow, M (1999) In Protein Science 8(12). p.20-2611
Abstract

Alpha1-microglobulin (alpha1m) is an electrophoretically heterogeneous plasma protein. It belongs to the lipocalin superfamily, a group of proteins with a three-dimensional (3D) structure that forms an internal hydrophobic ligand-binding pocket. Alpha1m carries a covalently linked unidentified chromophore that gives the protein a characteristic brown color and extremely heterogeneous optical properties. Twenty-one different colored tryptic peptides corresponding to residues 88-94, 118-121, and 122-134 of human alpha1m were purified. In these peptides, the side chains of Lys92, Lys118, and Lys130 carried size heterogeneous, covalently attached, unidentified chromophores with molecular masses between 122 and 282 atomic mass units (amu).... (More)

Alpha1-microglobulin (alpha1m) is an electrophoretically heterogeneous plasma protein. It belongs to the lipocalin superfamily, a group of proteins with a three-dimensional (3D) structure that forms an internal hydrophobic ligand-binding pocket. Alpha1m carries a covalently linked unidentified chromophore that gives the protein a characteristic brown color and extremely heterogeneous optical properties. Twenty-one different colored tryptic peptides corresponding to residues 88-94, 118-121, and 122-134 of human alpha1m were purified. In these peptides, the side chains of Lys92, Lys118, and Lys130 carried size heterogeneous, covalently attached, unidentified chromophores with molecular masses between 122 and 282 atomic mass units (amu). In addition, a previously unknown uncolored lipophilic 282 amu compound was found strongly, but noncovalently associated with the colored peptides. Uncolored tryptic peptides containing the same Lys residues were also purified. These peptides did not carry any additional mass (i.e., chromophore) suggesting that only a fraction of the Lys92, Lys118, and Lys130 are modified. The results can explain the size, charge, and optical heterogeneity of alpha1m. A 3D model of alpha1m, based on the structure of rat epididymal retinoic acid-binding protein (ERABP), suggests that Lys92, Lys118, and Lys130 are semiburied near the entrance of the lipocalin pocket. This was supported by the fluorescence spectra of alpha1m under native and denatured conditions, which indicated that the chromophores are buried, or semiburied, in the interior of the protein. In human plasma, approximately 50% of alpha1m is complex bound to IgA. Only the free alpha1m carried colored groups, whereas alpha1m linked to IgA was uncolored.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Animals, Chromatography, High Pressure Liquid, Color, Glycoproteins/chemistry, Humans, Immunoglobulin A/chemistry, Lysine/chemistry, Mass Spectrometry, Membrane Glycoproteins, Mice, Models, Molecular, Peptide Fragments/chemistry, Peptide Mapping, Rats, Sequence Alignment, Sequence Analysis, Protein, Spectrometry, Fluorescence, Trypsin Inhibitor, Kunitz Soybean
in
Protein Science
volume
8
issue
12
pages
20 - 2611
publisher
The Protein Society
external identifiers
  • pmid:10631976
  • scopus:0033233275
ISSN
0961-8368
DOI
10.1110/ps.8.12.2611
language
English
LU publication?
yes
id
94037ad8-c1e6-418c-87b5-ed341bb90d61
date added to LUP
2019-05-22 10:09:16
date last changed
2024-01-01 06:39:44
@article{94037ad8-c1e6-418c-87b5-ed341bb90d61,
  abstract     = {{<p>Alpha1-microglobulin (alpha1m) is an electrophoretically heterogeneous plasma protein. It belongs to the lipocalin superfamily, a group of proteins with a three-dimensional (3D) structure that forms an internal hydrophobic ligand-binding pocket. Alpha1m carries a covalently linked unidentified chromophore that gives the protein a characteristic brown color and extremely heterogeneous optical properties. Twenty-one different colored tryptic peptides corresponding to residues 88-94, 118-121, and 122-134 of human alpha1m were purified. In these peptides, the side chains of Lys92, Lys118, and Lys130 carried size heterogeneous, covalently attached, unidentified chromophores with molecular masses between 122 and 282 atomic mass units (amu). In addition, a previously unknown uncolored lipophilic 282 amu compound was found strongly, but noncovalently associated with the colored peptides. Uncolored tryptic peptides containing the same Lys residues were also purified. These peptides did not carry any additional mass (i.e., chromophore) suggesting that only a fraction of the Lys92, Lys118, and Lys130 are modified. The results can explain the size, charge, and optical heterogeneity of alpha1m. A 3D model of alpha1m, based on the structure of rat epididymal retinoic acid-binding protein (ERABP), suggests that Lys92, Lys118, and Lys130 are semiburied near the entrance of the lipocalin pocket. This was supported by the fluorescence spectra of alpha1m under native and denatured conditions, which indicated that the chromophores are buried, or semiburied, in the interior of the protein. In human plasma, approximately 50% of alpha1m is complex bound to IgA. Only the free alpha1m carried colored groups, whereas alpha1m linked to IgA was uncolored.</p>}},
  author       = {{Berggård, T and Lindqvist, A and Cedervall, T and Akerström, B and Thøgersen, I B and Enghild, J J and Cohen, A and Persson, P and Jönsson, J A and Silow, M}},
  issn         = {{0961-8368}},
  keywords     = {{Animals; Chromatography, High Pressure Liquid; Color; Glycoproteins/chemistry; Humans; Immunoglobulin A/chemistry; Lysine/chemistry; Mass Spectrometry; Membrane Glycoproteins; Mice; Models, Molecular; Peptide Fragments/chemistry; Peptide Mapping; Rats; Sequence Alignment; Sequence Analysis, Protein; Spectrometry, Fluorescence; Trypsin Inhibitor, Kunitz Soybean}},
  language     = {{eng}},
  number       = {{12}},
  pages        = {{20--2611}},
  publisher    = {{The Protein Society}},
  series       = {{Protein Science}},
  title        = {{Alpha1-microglobulin chromophores are located to three lysine residues semiburied in the lipocalin pocket and associated with a novel lipophilic compound}},
  url          = {{http://dx.doi.org/10.1110/ps.8.12.2611}},
  doi          = {{10.1110/ps.8.12.2611}},
  volume       = {{8}},
  year         = {{1999}},
}