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<strong>Proceedings</strong> of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Characteristics of a Human Cystatin C – Antibody ComplexAnna Sladewska 1 , Aneta Szymanska 1 , Aleksandra Kolodziejczyk 1 ,Anders Grubb 2 , and Paulina Czaplewska 11 Faculty of Chemistry,University of Gdansk, Gdansk; 2 Department of Clinical Chemistry,University Hospital, Lund, SwedenIntroductionThe immune system plays a major role in the defense of organisms against infections.Nowadays scientists are working on the use of antibodies in a search of inhibitors for manykinds of amyloidogenic diseases. The great potential of this concept is hidden inmonoclonal antibodies (mAb), which recognize only one epitope of the antigen and arehighly specific to this particular antigen. Grubb and coworkers described the influence ofmonoclonal antibodies on the dimerization process of human cystatin C (hCC). It wasfound that even catalytical amounts of monoclonal antibodies visibly diminished theprocess [1]. This clearly showed that the mAb can be considered as potential therapeuticagent in amyloidosis caused by aggregation of hCC and its L68Q mutant. Therefore, it isnecessary to develop sensitive analytical methods that enable to clarify details of theinteractions between amyloidogenic molecules. Recent developments show that selectiveproteolytic excision <strong>com</strong>bined with mass spectrometric peptide mapping (Epitope-Excision-MS) present high potential for the determination of epitopes for antigen-epitopemapping and for the identification of antibody paratope sequences [2].Results and DiscussionIn this work we present preliminary results of studies on the influence of the monoclonalantibody Cyst-13 on the dimerization process of human cystatin C and the identification ofthe epitope of this antibody with the use of mass spectrometric epitope extraction andexcision methods. The studies were carried out using amolecular affinity mass spectrometry approach. Themethod uses the resistance of the epitope sequenceagainst enzymatic digestions due to the shielding of the(105-114)Fig. 1. Location of binding sitefor <strong>com</strong>plex of hCC withmonoclonal antibodies Cyst-13.protein-antibody interaction site. Analysis of the MSspectra obtained in the proteolytic excision/extractionprocedure enabled us to identify and locate the epitope.The results of digestions by using different enzymesand the analysis of the MS spectra obtained atsuccessive steps of the extraction/excision proceduresrevealed that the epitope for mAb Cyst-13 <strong>com</strong>prisesthe residues 107-114 of human cystatin C(QGTMTLSK). The sequence was obtained after anepitope excision experiment on cystatin C–mAbFig. 2. Influence of Cyst13 mAb on hCC dimerization.286

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