The Role of Calcium in Calprotectin Dimerization as a Cancer Biomarker

Background: S100A8 and S100A9 as two subunits of heterodimeric calprotectin are identified mainly in leukocytes and are involved in inflammatory processes and several cancerous pathogens. This study was performed in order to evaluate the interaction of recombinant calprotectin subunits and to estimate calprotectin’s tertiary and secondary structures. Objectives: The aim of this study was to investigate the effects of calcium in calprotectin dimerization as a cancer biomarker. Materials and Methods: Heterodimeric calprotectin was formed with incubation of recombinant S100A8 and S100A9 subunits in the presence of Ca (1 mM), at 25 C for 15 minutes. Tertiary and secondary structures of S100A8, S100A9 and their complex were investigated, using fluorescence and circular dichroism (CD) spectroscopy, respectively. Results: Interaction of S100A8 and S100A9 in the presence of Ca2+ were revealed by decreasing the emission intensity of intrinsic fluorescence and increasing of the external fluorescence and also changes in the CD spectra of subunits after Ca2+ interactions. Conclusions: The expression of recombinant calprotectin, as an effective protein, can help in diagnosis or treatment of inflammatory and cancer processes in the future. Furthermore, Ca2+ induced a partial change in secondary and tertiary structure of calprotectin subunits and this change is probably necessary for protein dimerization.