common chemokine numbering (CCN)

Each secondary structural element (SSE) of the chemokine is given a designation (e.g., CX for Cys motif, B1 for B1-strand, etc), and each residue within an SSE is given an index (e.g., B1.1 is the first residue within the B1-strand. This system allows comparison of structurally equivalent positions across different chemokines. For instance, position B3.3 corresponds to C48 in CCL2 and C50 in CXCL12 due to differences in the length of their respective N-termini.