Briefly discuss the approach to classify chemokines and provide an example for each type.

Chemokines are small proteins, usually 8-12 kilodaltons in size, involved in chemotaxis (directed cell migration) and inflammatory responses. They act as signaling molecules by binding to specific receptors on target cells, such as leukocytes.

Chemokines can be classified based on the arrangement of their conserved cysteine residues (amino acids with a sulfur-containing side chain) near their N-terminus. There are four main types of chemokines: CC, CXC, CX3C, and XC. 1. CC chemokines: In this category, the two N-terminal cysteine residues are adjacent to each other. Example: CCL2 (MCP-1, Monocyte Chemoattractant Protein-1) 2. CXC chemokines: In this type, a single amino acid separates the two N-terminal cysteines. Example: CXCL8 (IL-8, Interleukiń-8) 3. CX3C chemokines: This chemokine class has three amino acids between the N-terminal cysteines. Example: CX3CL1 (Fractalkine) 4. XC chemokines: Here, only one cysteine residue is found near the N-terminus of the protein. Example: XCL1 (Lymphotactin)

To classify chemokines, refer to their cysteine residue arrangement at the N-terminus. The four main groups are CC, CXC, CX3C, and XC. Examples provided are CCL2, CXCL8, CX3CL1, and XCL1, respectively.