Comparison between intact and desialylated human serum amyloid P component by laser photo CIDNP (chemically induced dynamic nuclear polarization) technique: an indication for a conformational impact of sialic acid |
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Authors: | Hans-Christian Siebert Sabine Andre Gerd Reuter Robert Kaptein Johannes FG Vliegenthart Hans-Joachim Gabius |
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Institution: | (1) Bijvoet Center for Biomolecular Research, Utrecht University, PO Box 80075, NL-3508 TB Utrecht, The Netherlands;(2) Institut fur Physiologische Chemie, Tierarztliche Fakultat, Ludwig-Maximi lians-Universitat, Veterinarstr. 13, D-80539 Munchen, Germany |
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Abstract: | The human pentraxin serum amyloid P component (SAP) exhibits no microheterogeneity in its complex di-antennary glycan. To
elucidate whether the removal of sialic acids from this glycoprotein might affect the accessibility of certain amino acid
residues of the protein we employed the laser photo CIDNP approach as a sensitive tool. The CIDNP effect is generated by the
interaction of a photoexcited dye with reactive amino acids and results in enhanced absorption- or emission-signals which
can be observed for the three aromatic amino acids histidine, tryptophan, and tyrosine if they are accessible to the dye.
Therefore, this technique can be applied to explore surface exposure of these amino acid residues. The respective spectra
of SAP and enzymatically desialylated SAP were determined. Six tryptophan/histidine signals and one tyrosine signal are present
in the aromatic part of the CIDNP difference spectrum of SAP. The corresponding spectrum of desialylated SAP shows remarkable
alterations. The chemical shift of one Trp/His-characteristic signal is decreased by 0.1 ppm. One Trp/His-signal disappeared
and a new one was formed in the CIDNP difference spectrum of desialylated SAP, while the other signals were unaffected. The
Tyr signal has a clearly enhanced intensity in desialylated SAP. Therefore, the removal of sialic acid moieties from the single
N-glycan of each monomer apparently affects surface presentation of distinct CIDNP-reactive amino acids of SAP 1]. A conformational
change of the protein part of SAP in relation with a different orientation of the desialylated oligosaccharide chain in comparison
to the complete one is a possible explanation of our CIDNP results.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | human serum amyloid P component (SAP) chemically induced dynamic nuclear polarization (CIDNP) glycoprotein sialic acid protein conformation |
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