Resonance assignments of asymmetric tetrameric platelet factor 4 (PF4).

Platelet Factor 4 (PF4), also known as CXCL4, is a CXC chemokine crucial for hemostasis, inflammation, and immune responses. Under physiological conditions PF4 assembles into asymmetric tetramers (31.2 kDa) that are dimers of dimers with highly flexible N-terminal regions. PF4 tetramers play a central role in prothrombotic autoimmune conditions, such as heparin-induced thrombocytopenia (HIT), as well as vaccine-induced immune thrombocytopenia and thrombosis (VITT). Here, we report the resonance assignments of 1H, 15N, and 13C nuclei for wild-type asymmetric PF4 tetramers using TROSY-based triple resonance NMR experiments. We also used Nz-exchange spectroscopy to identify peaks split by slow-exchange between two distinct conformational states caused by the asymmetry of PF4 tetramers. Our NMR assignments establish a foundation for future investigations into the structural dynamics and functional mechanisms of PF4 as well as its pathological role in anti-PF4 disorders.