common chemokine receptor numbering (CRN)

The existing GPCRdb numbering scheme (see gpcrdb.org; Pándy-Szekeres, et al. 2023. Nucleic Acids Research) was used to refer to structurally equivalent positions across GPCR structures but with numbering that extends toward the receptor N-terminus to encompass a highly conserved Cys residue among chemokine GPCRs, which is designated 1x22. See Methods section of associated paper for details.