Carlson James, Baxter Sarah A, Dréau Didier, Nesmelova Irina V
Analytical Sciences Laboratory, David H. Murdock Research Institute, 150 Research Campus Dr., Kannapolis, NC 28081, USA.
Biochim Biophys Acta. 2013 Jan;1834(1):158-68. doi: 10.1016/j.bbapap.2012.09.010. Epub 2012 Sep 23.
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.
趋化因子是一大类蛋白质，作为化学引诱剂，参与许多生物学过程。特别是，趋化因子在正常和炎症条件下引导白细胞迁移。最近的研究表明，趋化因子之间的异嗜性相互作用显著影响其生物学活性，这可能代表了趋化因子活性的一种新的调节机制。体内血小板衍生趋化因子的共定位使它们能够相互作用。在这里，我们使用纳米喷雾电离质谱法筛选了11种不同的CXC和CC血小板衍生趋化因子，以寻找它们与血小板中两种最丰富的趋化因子CXCL4和CXCL7可能的相互作用。结果表明，许多筛选出的趋化因子（尽管不是全部）与CXCL4和/或CXCL7形成异二聚体。特别是，在CXCL12与CXCL4或CXCL7之间观察到强烈的异二聚化。与其他趋化因子相比，CXCL12的主要结构差异在于其C末端α螺旋相对于β折叠的方向和堆积。使用分子动力学（MD）轨迹对CXCL4/CXCL12异二聚体的一种可能结构（CXC型结构）进行分析，结果显示CXCL4可能经历构象转变以改变α螺旋方向。在这个新方向上，CXCL4的α螺旋与CXCL12的α螺旋平行排列，这是一种能量上更有利的构象。此外，我们通过从人血小板中进行共免疫沉淀确定CXCL4和CXCL12通过物理相互作用形成异二聚体。总体而言，我们的结果突出表明许多血小板衍生趋化因子能够进行异嗜性相互作用，并有力地支持了对这些相互作用的生物学影响的未来研究。
