Crystal structure of Epstein-Barr virus protein BCRF1, a homolog of cellular interleukin-10

The crystal structure of Epstein-Barr virus protein BCRF1, an analog of cellular interleukin-10 (IL-10), has been determined at the resolution of 1.9 Angstrom and refined to an R-factor 0.191. The structure of this cytokine is similar to that of human IL-10 (hIL-10), forming an intercalated dimer of two 17 kDa polypeptides related by a crystallographic 2-fold symmetry axis. BCRF1 exhibits novel conformations of the N-terminal coil and of the loop between helices A and B compared to hIL-10. These regions are likely to be involved in binding of one or more components of the IL-10 receptor system, and thus the structural differences may account for the lower binding affinity and limited spectrum of biological activities of viral IL-10, compared to hIL-10. (C) 1997 Academic Press Limited.