vCCI:vMIP-II complex

 “Biophysical and Computational Studies of the vCCI:vMIP-II complex”

Anna F. Nguyen, Nai-wei Kuo, Laura Showalter, Ricardo Ramos, Cynthia M. Dupureur, Michael E. Colvin and Patricia J. LiWang International Journal of Molecular Sciences 18:8 DOI 10.3390/ijms18081778 (2017).

Abstract: Certain viruses have the ability to subvert the mammalian immune response, including interference in the chemokine system.  Poxviruses produce the chemokine binding protein vCCI (viral CC chemokine Inhibitor; also called 35K), which tightly binds to CC chemokines.  To facilitate the study of vCCI, we first provide a protocol to produce folded vCCI from E. coli.  It is shown here that vCCI binds with unusually high affinity to vMIP-II, a chemokine analog produced by the virus, HHV-8.  Fluorescence anisotropy was used to investigate the vCCI:vMIP-II complex and shows that vCCI binds to vMIP-II with a higher affinity than most other chemokines, having a Kd of 0.06 ± 0.006 nM.  NMR chemical shift perturbation experiments indicate that key amino acids used for binding in the complex are similar to those found in previous work.  Molecular dynamics were then used to compare the vCCI:vMIP-II complex with the known vCCI:MIP-1β/CCL4 complex. The simulations show key interactions such as those between E143 and D75 in vCCI/35K and R18 in vMIP-II.  Further, in a comparison of 1 usec MD trajectories, vMIP-II shows more overall surface binding to vCCI than does the chemokine MIP-1β.  vMIP-II maintains unique contacts at its N-terminus to vCCI that are not made by MIP-1β, and vMIP-II also makes more contacts with the vCCI flexible acidic loop (located between the second and third beta strands) than does MIP-1β. These studies provide evidence for the basis of the tight vCCI:vMIP-II interaction while elucidating the vCCI:MIP-1β interaction, and allow insight into the structure of proteins that are capable of broadly subverting the mammalian immune system.