Unveiling the molecular mechanism of chemokine oligomerization and GAG interactions using TIMS in combination with PSA methods


Chemokines are a group of small (~8-14kDa), mostly basic, structurally related molecules that regulate cell trafficking of various types of leukocytes through interactions with a subset of seven-transmembrane, G protein-coupled receptors. However, inappropriate function may lead to a series of pathologies including inflammatory disease, atherosclerosis, cancer and AIDS. Chemokine oligomerization and their interaction with glycosamonoglycans (GAGs) appear coupled and linked to cell migration. Therefore, we study how chemokine homo- and heter-oligomerize and how they interact with GAGs in order to regulate signal transduction and intercellular communication.

Figure 1: Healthy and inflamed cells have different abundances and types of chemokines and GAGs and tansduce different cellular signals.

Although chemokine monomers are able to bind receptors, oligomeric forms are found responsible. Apart from homo-oligomers, chemokines also form hetero-oligomers. GAG-binding is found involved in chemokine oligomerization. The highly heterogeneous GAGs could induce different chemokine structures, which in turn lead to specific cell migration process. As illustrated in Figure 1, healthy and inflamed cells have different abundances and types of chemokines and GAGs. As a consequence, the oligomeric steady-state can be altered and a different cellular signal can be induced. It is hard to define general mechanisms as every chemokine may have its own unique oligomerization mechanism. And it's challenging for conventional methods like NMR or X-ray to study chemokine system as chemokine structures are in dynamic equilibrium between different oligomeric states.


We use ion mobility mass spectrometry (IM-MS) to study structures of chemokine and their oligomers. Using ESI to transfer intact molecular complex from solution to the gas phase, IM-MS is fast and sensitive. Ion mobility separation eliminates the complexity resulted from the heterogeneity of GAGs. And as the IM/MS method takes "structural snapshots" of the entire conformational ensemble, structural information for co-existing and interconverting chemokine oligomers can be obtained.