A low-molecular-weight cationic protein that can bind human and rabbit immunoglobulins G has been isolated from Yersinia pseudotuberculosis cells. This immunoglobulin binding protein (IBP) interacts with IgG Fc-fragment, the association constant of the resulting complex being 3.1 microM(-1). MALDI-TOF mass spectrometry analysis of IBP revealed its molecular mass of 16.1 kDa, and capillary isoelectrofocusing analysis showed pI value of 9.2. N-Terminal sequence determination by Edman degradation revealed the sequence of the 15 terminal amino acid residues (ADKIAIVNVSSIFQ). Tryptic hydrolysate of IBP was subjected to MALDI-TOF mass spectrometry for proteolytic peptide profiling. Based on the peptide fingerprint, molecular mass, pI, and N-terminal sequence and using bioinformatic resources, IBP was identified as Y. pseudotuberculosis periplasmic chaperone Skp. Using the method of comparative modeling a spatial model of Skp has been built. This model was then used for modeling of Skp complexes with human IgG1 Fc-fragment by means of molecular docking.
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