The heterodimerization of platelet-derived chemokines. Biochimica et Biophysica Acta (BBA)- Proteins and Proteomics. January 2013. James Carlson, Sarah A. Baxter, Didier Dréau, Irina V. Nesmelova.
Analytical Sciences Laboratory, David H. Murdock Research Institute and the Department of Biology, Department of Physics and Optical Science and the Center for Biomedical Engineering and Science, University of North Carolina at Charlotte.
Chemokines encompass a large family of proteins that act as chemoattractants and are involved in many biological processes. In particular, chemokines guide the migration of leukocytes during normal and inflammatory conditions. Recent studies reveal that the heterophilic interactions between chemokines significantly affect their biological activity, possibly representing a novel regulatory mechanism of the chemokine activities. The co-localization of platelet-derived chemokines in vivo allows them to interact. Here, we used nano-spray ionization mass spectrometry to screen eleven different CXC and CC platelet-derived chemokines for possible interactions with the two most abundant chemokines present in platelets, CXCL4 and CXCL7. Results indicate that many screened chemokines, although not all of them, form heterodimers with CXCL4 and/or CXCL7. In particular, a strong heterodimerization was observed between CXCL12 and CXCL4 or CXCL7. Compared to other chemokines, the main structural difference of CXCL12 is in the orientation and packing of the C-terminal alpha-helix in relation to the beta-sheet. The analysis of one possible structure of the CXCL4/CXCL12 heterodimer, CXC-type structure, using molecular dynamics (MD) trajectory reveals that CXCL4 may undergo a conformational transition to alter the alpha helix orientation. In this new orientation, the alpha-helix of CXCL4 aligns in parallel with the CXCL12 alpha-helix, an energetically more favorable conformation. Further, we determined that CXCL4 and CXCL12 physically interact to form heterodimers by co-immunoprecipitations from human platelets. Overall, our results highlight that many platelet-derived chemokines are capable of heterophilic interactions and strongly support future studies of the biological impact of these interactions.
► We report new platelet-derived chemokine heterodimers detected by mass spectrometry ► Several strong heterodimers were observed, including CXCL4/CXCL12 heterodimer ► The stability of CXCL4/CXCL12 heterodimer was confirmed using MD simulations ► In vivo relevance of this heterodimer was confirmed by Co-IP from human platelets ► Results strongly support future functional studies of chemokine heterodimers