Semi-Synthesis of an Evasin from Tick Saliva Reveals a Critical Role of Tyrosine Sulfation for Chemokine Binding and Inhibition

Blood feeding arthropods produce anti-inflammatory salivary proteins called evasins that function through inhibition of chemokine-receptor signalling in the host. Herein, we show that the evasin ACA-01 from the Amblyomma cajennense tick can be post-translationally sulfated at two tyrosine residues, albeit as a mixture of sulfated variants. Homogenously sulfated variants of the proteins were efficiently assembled via a semi-synthetic native chemical ligation strategy. Sulfation significantly improved the binding affinity of ACA-01 for a range of pro-inflammatory chemokines and also enhanced the ability of ACA-01 to inhibit chemokine signalling through cognate receptors. Comparisons of evasin sequences and structural data suggest that tyrosine sulfation serves as a receptor mimetic strategy for recognizing and suppressing the pro-inflammatory activity of a wide variety of mammalian chemokines. As such, the use incorporation of this PTM or mimics thereof into evasins may provide a strategy to optimize these salivary tick proteins for anti-inflammatory applications