Crystal structure of TNFalpha complexed with a poxvirus MHC-related TNF binding protein

Abstract

The poxvirus 2L protein binds tumor necrosis factor-alpha (TNFalpha) to inhibit host antiviral and immune responses. The 2.8-A 2L-TNFalpha structure reveals three symmetrically arranged 2L molecules per TNFalpha trimer. 2L resembles class I major histocompatibility complex (MHC) molecules but lacks a peptide-binding groove and beta2-microglobulin light chain. Overlap between the 2L and host TNF receptor-binding sites on TNFalpha rationalizes 2L inhibition of TNFalpha-TNF receptor interactions and prevention of TNFalpha-induced immune responses.

Figure 1

Structure of 2L–TNFα and comparison with TNFR1–TNFβ. Disulfide bonds and ordered carbohydrates on 2L are shown as yellow sticks. Left, the 2L–TNFα complex shown as a ribbon diagram in two orientations: looking down the three-fold symmetry axis (above) and with the three-fold axis vertical (middle). Below left, a surface representation of TNFα from the complex structure, with the 2L-binding site highlighted in red at one of three interfaces on the TNFα trimer (TNFα subunits are different shades of blue). Right, The TNFR1–TNFβ structure shown as a ribbon diagram in analogous orientations (top and middle). Below right, a surface representation of TNFβ from the complex structure with one of the TNFR1-binding sites highlighted in red.

Figure 2

The 2L–TNFα interface. (a) Surface representations of 2L (left) and the 2L–TNFα complex (right). 2L is magenta and TNFα subunits are different shades of blue-green. Contact surfaces (≤4.0 Å) are highlighted in blue on 2L and red on TNFα. (b) Ribbon diagrams corresponding to the surfaces shown above. The C terminus of 2L is distant from the TNFα-binding site, rationalizing why truncations in this region did not affect binding to TNFα. (c) Stereo close-up view of 2L–TNFα interface, with the α3 domain insertion highlighted in blue.