posted on 2023-01-10, 19:05authored byYa-Hsin Liu, Chia-Hsuan Chuang, Yi-Zong Lee, Eh-Tzen Lee, Chiao-Ling Lo, Chu-Ya Wu, Li-Kun Huang, Andreas Bikfalvi, Shih-Che Sue
Chemokine CXCL4L1, a homologue of CXCL4, is a more potent
antiangiogenic
ligand. Its structural property is correlated with the downstream
receptor binding. The two chemokines execute their functions by binding
the receptors of CXCR3A and CXCR3B. The receptors differ by an extra
51-residue extension in the CXCR3B N-terminus. To understand the binding
specificity, a GB1 protein scaffold was used to carry different CXCR3
extracellular elements, and artificial CXCL4 and CXCL4L1 monomers
were engineered for the binding assay. We first characterized the
molten globule property of CXCL4L1. The structural property causes
the CXCL4L1 tetramer to dissociate into monomers in low concentrations,
but native CXCL4 adopts a stable tetramer structure in solution. In
the titration experiments, the combination of the CXCR3A N-terminus
and receptor extracellular loop 2 provided moderate and comparable
binding affinities to CXCL4 and CXCL4L1, while sulfation on the CXCR3A
N-terminal tyrosine residues provided binding specificity. However,
the CXCR3B N-terminal extension did not show significant enhancement
in the binding of CXCL4 or CXCL4L1. This result indicates that the
tendency to form a chemokine monomer and the binding affinity together
contribute the high antiangiogenic activity of CXCL4L1.