Structural study of the interaction between poxvirus-encoded cc chemokine inhibitor vcci and human mip-1beta

Chemokines (chemotactic cytokines) comprise a large family of proteins that recruit and activate leukocytes, giving chemokines a major role in both immune response and inflammation-related diseases. Viral CC chemokine inhibitor (vCCI) is a poxvirus encoded protein that has been shown to bind tightly and inhibit the action of many CC chemokines. This function suggests that vCCI could be explored as an antiinflammatory therapeutic, a possibility that has been supported in mouse studies. The structure of vCCI in unbound form was determined by others, but to date no structure has been reported of bound vCCI. We report the NMR structure of vCCI in complex with the human CC chemokine MIP-1[beta]. The non-aggregating MIP-1[beta] variant MIP-1[beta] 45AASA48 was used in this complex to allow sufficiently high concentration at pH 7 to carry out the solution structure determination. A combination of NOE distance restraints, torsion angle restraints, and residual dipolar coupling were used to determine the structure of the complex, which also required protein deuteration due to its relatively large size (34kDa). The structure shows that MIP-1[beta] binds to vCCI with 1:1 stoichiometry, forming a complex of 311 amino acids. vCCI uses residues from its [beta]- sheet II to interact with a surface of MIP-1[beta] that includes residues adjacent to its Nterminus, as well as residues in the 20's region, and the 40's loop. The structure of the MIP-1[beta]-vCCI complex reveals for the first time the regions of each protein involved in the interaction, and allows a greater understanding of the strategy used by vCCI to tightly bind numerous chemokines, while retaining selectivity for the CC chemokine subfamily