Massenspektrometrische Identifizierung und Charakterisierung von posttranslationalen Modifikationen bei pathologischen freien Antikörperleichtketten
In dieser Arbeit wurden die freien Antikörperleichtketten von Patienten mit Multiplen Myelom bzw. mit Multiplen Myelom und AL-Amyloidose auf das Auftreten von posttranslationalen Modifikationen mit der Hilfe von MS/MS-Spektren analysiert. Beide Patientengruppen zeichnen sich durch eine Überproduktio...
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| Format: | Doctoral Thesis |
| Language: | deu |
| Published: |
2014
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| Online Access: | https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/10827 http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-108275 https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-108275 https://opus.bibliothek.uni-wuerzburg.de/files/10827/KatjaHeinig_Dissertation_end.pdf |
| Summary: | In dieser Arbeit wurden die freien Antikörperleichtketten von Patienten mit Multiplen Myelom bzw. mit Multiplen Myelom und AL-Amyloidose auf das Auftreten von posttranslationalen Modifikationen mit der Hilfe von MS/MS-Spektren analysiert. Beide Patientengruppen zeichnen sich durch eine Überproduktion von monoklonalen Antikörperleichtketten aus, wobei diese bei Multiplen-Myelom-Patienten löslich und bei den AL-Amyloidose-Patienten unlöslich vorliegen. Zur Vorbereitung der massenspektrometrischen Messungen wurden die FLCs aus den Knochenmarksüberständen der Patienten isoliert. Dafür wurde eine 2-Schritt-Aufarbeitungsmethode etabliert, bei der mit Hilfe einer Affinitätschromatographie und einer präparativen SDS-PAGE die FLCs aus einer komplexen Matrix isoliert werden konnten. Mit Hilfe der MS/MS-Messungen konnten Sulfonierungen, Methylierungen, Acetylierungen, Oxidierungen und eine O-Glykosylierung identifiziert werden.
In einem weiteren Schritt wurden mittels Varianzanalyse Sequenzen von AL-Amyloidose- und Multiplen-Myelom-Patienten sowie von Kontrollprobanten hinsichtlich der Verteilung der Aminosäuren statistisch analysiert. Dabei konnten mehrere Stellen im FLC-Peptid identifiziert werden, an denen bestimmte Aminosäuren in Abhängigkeit der Subgruppe signifikant unterschiedlich vorkommen. === This work analyzed posttranslational modifications of pathological free light chains (FLC) from patients who suffer from multiple myeloma or multiple myeloma and AL amyloidosis. Both patient groups show an overproduction of free light chains which are soluble in multi- ple myeloma patients and insoluble in AL amyloidosis patients. One reason for the different solubility of the free light chains may be the appearance of posttranslational modifications.
In order to identity posttranslational modifications FLCs from bone marrow supernatant were isolated and mass spectrometrically analyzed using Orbitrap technology. All measurements were done with three samples of each patient subgroup. For the FLC purification a 2-step method was established which isolates FLCs with affinity chromatography and preparative SDS-PAGE. This method enables the purification of the FLCs from a complex matrix where the FLCs may not be the main component.
Before mass spectrometric analyses the amino acid sequences of the FLCs were determined via PCR using FLC-specific primers. The subsequent mass spectrometric analyses verified between 92 % and 100 % of the amino acid sequences.
The analysis of posttranslational modifications identified for each patient a sulfonation at cysteine C194 whose identity and localization were verified with HCD and ETD fragmen- tation mass spectrometry technology. A similar cysteine sulfonation of FLCs was found by Connors et al. [10] who identified an identical PTM on cysteine C214 in FLCs from AL amyloidosis patients. However, a sulfonation on cysteine C194 and in FLCs from multiple myeloma patients was not published before.
Furthermore, a methylation of cysteine C194 was found for each sample. As for the sul- fonation, no disease-specific appearance of methylation could be revealed. This may be a consequence of a limited number of available samples.
In addition, a GlcNAc-glycosylation in the N-terminus of the variable region was found for the patients SP 1070, WS 1199 and GI 1206. An exact localization of the PTM was not possible because of the loss of the PTM during HCD fragmentation and the lack of conve- nient ETD spectra.
Moreover FLC sequences were analyzed statistically for the distribution of amino acids. Therefore, a multiple sequence alignment with sequences from multiple myeloma and AL amyloidosis patients as with sequences from healthy control group individuals was done. Subsequently, for each position in FLC sequence the most frequent amino acids were deter- mined and the frequencies of being the most frequent amino acid for each subgroup were calculated. As a result, positions 56 and 73 were identified where serine respectively leucine occur statistcally significantly more often in the control group than in the multiple myeloma or the AL amyloidosis subgroup. The comparison of the frequencies of the multiple myeloma and AL amyloidosis subgroup revealed significant differences at the positions 31 and 61. At the position 31 in AL amyloidosis subgroup asparagine appears more often than in the mul- tiple myeloma subgroup which may indicate that asparagine at this position enhances the bias to FLC accumulation. The position 31 was also described as influential by Stevens et al. [25], although in his studies an aspartic acid at this position increases the bias to aggregation.
At position 61 an arginine exists more often in the multiple myeloma than in the AL amy- loidosis subgroup where the missing of an arginine at this position seems to enhance the tendency for FLC accumulation. This result is consistent with the findings by Hurle et al. [27, 28] and may be a result of a missing salt bridge from arginine R61 to aspartic acid D82. |
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