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- Berggård, T, et al.
(författare)
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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
- 1999
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Ingår i: Protein Science. - : Wiley. - 0961-8368. ; 8:12, s. 20-2611
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Tidskriftsartikel (refereegranskat)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). 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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- Cedervall, M, et al.
(författare)
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Efficient maximum likelihood DOA estimation for signals with known waveforms in the presence of multipath
- 1997
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Ingår i: IEEE TRANSACTIONS ON SIGNAL PROCESSING. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. ; 45:3
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a large-sample maximum likelihood (ML) algorithm for estimating the directions of arrival (DOA's) and signal amplitudes of known, possibly coherent signals impinging on an array of sensors, The algorithm is an extension of the DEML method of Li
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- Cedervall, M, et al.
(författare)
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Mode-type algorithm for estimating damped, undamped, or explosive modes
- 1997
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Ingår i: CIRCUITS SYSTEMS AND SIGNAL PROCESSING. - : BIRKHAUSER BOSTON INC. - 0278-081X. ; 16:3, s. 349-362
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We propose a new algorithm for estimating the parameters of damped, undamped, or explosive sinusoidal signals. The algorithm resembles the MODE algorithm, which is commonly used for direction of arrival estimation in the array signal processing held. It i
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- Cedervall, M, et al.
(författare)
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System identification from noisy measurements by using instrumental variables and subspace fitting
- 1996
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Ingår i: CIRCUITS SYSTEMS AND SIGNAL PROCESSING. - : BIRKHAUSER BOSTON INC. - 0278-081X. ; 15:2, s. 275-290
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper considers the estimation of the parameters of a linear discrete-time system from noise-perturbed input and output measurements. The conditions imposed on the system are fairly general. In particular, the input and output noises are allowed to b
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- Cedervall, T, et al.
(författare)
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Coiled-coil structure of group A streptococcal M proteins. Different temperature stability of class A and C proteins by hydrophobic-nonhydrophobic amino acid substitutions at heptad positions a and d
- 1997
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 36:16, s. 4987-4994
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Tidskriftsartikel (refereegranskat)abstract
- M proteins and M-like proteins, expressed on the surface of group A streptococci and binding to human plasma proteins, can be divided into two classes, A and C, depending on the structure of the central repeated regions. The class C proteins have been shown to be dimers with a coiled-coil structure. In this work, we have compared the structure and binding of a class A protein, Mrp4, and a class C protein, Arp4, expressed by the same bacterial strain. Circular dichroism spectra, gel filtration, and binding assays showed that both proteins had a coiled-coil dimer configuration and a high-affinity binding at 20 degrees C. However, striking differences were seen at 37 degrees C. The class A protein, Mrp4, was still a coiled-coil dimer with high affinity binding activity, whereas the class C protein, Arp4, had lost both the coiled-coil structure and binding activity. Raising the temperature even higher, Mrp4 retained the coiled-coil structure up to 70-90 degrees C. Furthermore, a recombinant protein, Mrp(C), in which the A-repeats of Mrp4 were replaced by the C-repeats of Arp4, lost its coiled-coil structure and fibrinogen-binding around 40-45 degrees C. These results suggest a high thermal stability of class A proteins and a low stability of class C proteins and that the structural basis for this can be found partly in the A- and C-repeats. Analysis of the amino acid sequences of the A- and C-repeats, revealed a large difference, 87% and 45%, respectively, in the content of hydrophobic amino acid residues in the positions regarded as important for the formation of the coiled-coil structure. In particular, several alanine residues in the A-repeats were replaced by serine residues in the C-repeats. Our results suggest that important structural and functional changes within the M protein family have evolved by specific hydrophobic-nonhydrophobic amino acid replacements.
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