Complete crystal structure of monocyte chemotactic protein-2, a CC chemokine that interacts with multiple receptors

Monocyte chemotactic protein 2 (MCP-2) is a CC chemokine that utilizes mult iple cellular receptors to attract and activate human leukocytes. MCP-2 is a potent inhibitor of HIV-1 by virtue of its high-affinity binding to the r eceptor CCR5, one of the major coreceptors for HIV-1. Although a few struct ures of CC chemokines have been reported, none of these was determined with the N-terminal pyroglutamic acid residue (pGlu1) and a complete C-terminus . pGlu1 is essential for the chemotactic activity of MCP-2. Recombinant MCP -2 has Gln1 at the N terminus, 12-15% of which cyclizes automatically and f orms pGlu1. The chemotactic activity of such MCP-2 mixture, which contains 12-15% pGlu1-form and 85-88% Gln1-form protein, is similar to 10 times lowe r when compared with that of fully cyclized MCP-2 preparation. Therefore, t his chemokine is practically inactive without pGlu1. We have determined the complete crystal structure of MCP-2 that contains both pGlu1 and an intact C-terminus. With the existence of pGlu1, the conformation of the N-terminu s allows two additional interactions between the two subunits of MCP-2 dime r: a hydrogen bond between pGlu1 and Asn17 and a salt bridge between Asp3 a nd Arg18. Consequently, both pGlu1 are anchored and buried, and thereby, bo th N-terminal regions are protected against protease degradation. We have a lso observed not previously reported extended helical nature of the C termi nal region, which covers residues 58-74.