H, N and C resonance assignments of Ixolaris, a tissue factor pathway inhibitor from the tick salivary gland.

Ixolaris is a two-Kunitz tick salivary gland protein identified in Ixodes scapularis that presents sequence homology to TFPI (tissue factor pathway inhibitor). It binds to the coagulation enzyme factor Xa (FXa) or to its zymogen form, FX, and further inhibits tissue factor/FVIIa complex (extrinsic Xnase compex). Differently from TFPI, Ixolaris does not bind to the active site cleft of FXa. Instead, complex formation is mediated by the FXa heparin-binding exosite, which may also results in decreased FXa activity into the prothrombinase complex. The Ixolaris-FXa/FX complex formation has been characterized by using a combination of biophysical and biochemical technics although no structural data is currently available. In this study, we reported the NMR chemical shift assignment of Ixolaris, as a first step to further establishing the structure, dynamics and function relationship for this protein.